Abdominals

Reading time:

There are four main abdominals: the rectus abdominis, the external oblique, the internal oblique, and the transverse abdominis. They originate either from the iliac crest, pubis and inguinal ligament, or from the lower ribs and costal ligaments. They insert on a number of attachment sites, including the xiphoid process, linea alba, costal ligaments, and iliac and pubic crest. 

The abdominal muscles function as spinal flexors, rotators and lateral flexors, as well producing spinal stiffness and stability. The rectus abdominis is the primary spinal flexor owing to its attachments that extend across the middle of the abdomen, while the external oblique is the primary spinal rotator and lateral flexor.

The abdominals vary in size, weight and muscle architecture. The rectus abdominis displays the greatest muscle thickness, the longest muscle fascicles, but the smallest pennation angle. The external oblique has the largest pennation angle and is the heaviest, while the transverse abdominis is the lightest, at around half its weight. The muscle size and pennation angle of the abdominals also display considerable regional variation.

The abdominals display a mixed proportion of type I and type II muscle fibers, with type I muscle fiber proportion ranging between 55 – 58% across the rectus abdominis, internal oblique, and external oblique. This may imply that training with a combination of lighter and heavier loads is beneficial for this muscle.

The rectus abdominis and external oblique display moderate levels of muscle activity during squat and deadlift variations, but there is no difference in muscle activity of the abdominals between the squat and deadlift. They are highly active during less traditional, compound exercises such as the strongman tire flip, atlas stone lift and shouldered keg walk.

Rectus abdominis and external oblique muscle activity levels are both greater in the standing overhead press, plank, and Swiss ball jack knife compared to the squat and deadlift. Despite the popularity of unstable surface training for developing the trunk musculature, many unstable multi-joint exercises do not produce superior muscle activity compared to their stable equivalents.

During deadlifts, rectus abdominis and external oblique muscle activity levels are moderate, indicating that it may be a useful exercise for the abdominals. Exercise technique (conventional or sumo) does not affect rectus abdominis or external oblique muscle activity, but muscle activity is greater in the ascending phase than in the descending phase. Surface stability in the deadlift does not affect muscle activity of the abdominals.

During the squat, increasing relative load leads to greater external oblique muscle activity but does not alter rectus abdominis or transverse abdominis muscle activity. Muscle activity of the abdominals appears to be similar across almost all possible squat variations (back, front overhead, machine, and elastic band-resisted), although the external oblique may display greater muscle activity in the split squat than in the back squat.

During the squat, internal cues seem to produce greater transverse abdominis muscle activity and higher external oblique muscle activity than no internal cues. In contrast, using a weightlifting belt and using unstable surfaces have no effect on the muscle activity of the abdominals.

Sit ups (hip flexion with or without trunk flexion) can be performed with either anchored or unanchored feet and with either bent legs or straight legs. A variation on the sit up that only involves trunk flexion and does not involve hip flexion is known as the curl up or crunch. The curl up can also be performed with either bent legs or straight legs.

Rectus abdominis muscle activity is similar in sit ups and curl ups but external oblique muscle activity is higher in sit ups than curls ups. Rectus abdominis muscle activity is similar in all curl up variations. External oblique muscle activity is highest in the curl up variation with trunk rotation.

Adding external load and using an unstable surface during curl ups leads to greater rectus abdominis and external oblique muscle activity. Using internal cues to focus on the muscle does not improve rectus abdominis muscle activity but leads to preferentially more external oblique muscle activity.

Rectus abdominis muscle activity is higher when performing the kneeling roll out, hanging leg raises and in some cases the reverse curl up compared to sit up and curl up exercises. External oblique muscle activity is higher during a number of dynamic isolation exercises compared to the sit up and curl up including the kneeling roll out, horizontal side bend, jack knife, hanging leg raise.

Integrated core exercise, including whole-body linkage and dynamic stabilisation exercises, are commonly-used for developing the abdominals. However, only the plank with arm reach and side plank with arm reach can outperform traditional curl ups for rectus abdominis and external oblique muscle activity. 

Unstable surface dynamic core exercises, usually performed on a Swiss ball, are commonly used for training the abdominals. However, only the Swiss ball jack knife can outperform curl ups for rectus abdominis and external oblique muscle activity.

Increasing external moment arm lengths during isometric core exercise, either by using extended legs during hanging leg raises, or by performing long lever planks, leads to greater rectus abdominis and external oblique muscle activity.

During isometric core exercise, rectus abdominis and external oblique muscle activity are higher when using posterior pelvic tilt than when using abdominal hollowing, and when using unstable surfaces than when using stable ones.


CONTENTS

Full table of contents

  1. Anatomy
  2. Muscle architecture
  3. Muscle fiber type
  4. Electromyography (EMG)
  5. References
  6. Contributors
  7. Provide feedback


ANATOMY

PURPOSE

This purpose of this section is to provide a summary of the anatomy of the abdominal musculature.

ORIGINS AND INSERTIONS

Introduction

The origins and insertions describe where muscles are attached to the skeleton, via connective tissue. Basic conclusions can be drawn about the function of muscles from their origins and insertions. There are four main abdominal muscles to consider: the rectus abdominis, the external oblique, the internal oblique, and the transverse abdominis. The origins and insertions of the rectus abdominis are such that the muscle extends the length of the abdomen from the pubis to the lower 3 ribs and sternum. This muscle is also separated by a central fibrous structure through its midline called the linea alba, resulting in a left and right muscle belly. The external oblique originates from the outer surfaces of the lower 8 ribs and insert on to the linear alba and anterior half of the iliac crest. The internal oblique originates from the anterior two thirds of the iliac crest and the lateral half of the inguinal ligament and inserts into the lower 3 – 4 costal connective tissue, the linear alba and pubic crest. The transverse abdominis originates from the inner surface of the lower 6 costal connective tissue, the anterior 2/3 of the iliac crest, and is also connected to the tensor fasciae latae, lateral third of the inguinal ligament and inserts to the linea alba and pelvis (Teyhen et al. 2007).

Origins

The rectus abdominis originates from the crest of the pubis, which extends along the length of the abdomen. The muscle is separated at the midline by a fibrous structure called the linea alba that also spans the length of the abdomen from the pubis to the sternum. The linea alba splits the rectus abdominis into a left and right muscle belly and functions as an attachment site for other abdominal muscles (Teyhen et al. 2007). The external oblique originates from the outer surfaces of the lower 8 ribs such that it comprises the lateral abdominal wall muscles with the internal oblique and transverse abdominis. The internal oblique originates at its highest level on the anterior two thirds of iliac crest, and at its lower level the inguinal ligament. The transverse abdominis covers a large area of the abdomen. It is considered a deep abdominal muscle, as it lies underneath the other abdominals. It originates laterally from the lower 6 ribs, the tensor fasciae latae, and iliac crest.

Insertions

The rectus abdominis inserts on the lower 3 ribs, as well as the xiphoid process of the sternum. The external oblique has its primary insertions on the linea alba and the anterior half of the iliac crest. The internal oblique inserts on to the lower 4 costal ligaments, linea alba and pubic crest. The transverse abdominis inserts to the linea alba and pubic crest.

Muscle function

Owing to the attachment sites of the abdominals, the muscles are likely to function during similar tasks. The rectus abdominis is the primary flexor of the spine given its large attachment sites at the pelvis and ribcage, and fascicle orientation (Lehman et al. 2001; Delp et al. 2001). Further, since the abdominal muscles attach to the pelvis and ribcage, each muscle has a force producing potential in flexion or twisting motions. The external oblique extends from the front of the lateral pelvis to the side of the lower ribs and thus is highly active during spine rotation (McGill et al. 1991) and lateral flexion (Konrad et al. 2001). Indeed, a primary function of the abdominal muscles is to stabilise the spine (Cholewicki & McGill, 1996). The transverse abdominis, internal and external oblique display the greatest potential to function as spinal stabilisers. Teyhen et al. (2007) reported that these muscles function to provide mechanical stability to the spine by contracting against the intra-abdominal pressure of the abdominal cavity and thus increasing the stiffness of the lumbar spine against external loads. However, the rectus abdominis may also function to stabilise the spine by way of cocontraction with the erector spinae and thus increasing joint stiffness. Additionally, it appears the internal oblique and the transverse abdominis contribute to sacroiliac joint stability by producing force closure by exerting a compressive force  on to the joint (Snyder et al. 1995).

OVERALL WEIGHT & SIZE

Introduction

The size and weight of muscles can be measured in various ways. The most common ways to measure muscle size are by volume or by anatomical cross-sectional area. In addition, muscle weight and size can be presented either in absolute terms or relative to other muscles.

Muscle weight

Very few studies have assessed the weight of the abdominals. Brown et al. (2011) reported muscle weights of the rectus abdominis, external oblique, internal oblique, and transverse abdominis of 81g, 105g, 75g, and 51g, respectively. It appears that the external oblique is the heaviest of the abdominals.

Muscle cross-sectional area

Very little data exists regarding the cross-sectional area of the abdominals whereby the oblique muscles and transverse abdominis appear to be too large to measure via ultrasound. However, Rankin et al. (2006) reported that the cross-sectional area of the rectus abdominis was 8.27cm2. Additionally, the abdominal muscles appear to vary in their morphology across the abdomen Rankin et al. (2006) reported that the rectus abdominis and transverse abdominis were larger when measured just below the rib cage, while the internal and external oblique were larger when measured at the mid point between the superior iliac crest and rig cage. Further, Teyhen et al. (2007) reported that the upper portions of the lateral wall are generally thicker. Therefore, regional measurements may be more appropriate in assessing the size of these muscles.

SECTION CONCLUSIONS

There are four main abdominals: the rectus abdominis, the external oblique, the internal oblique, and the transverse abdominis. They originate either from the iliac crest, pubis and inguinal ligament, or from the lower ribs and costal ligaments. They insert on a number of attachment sites, including the xiphoid process, linea alba, costal ligaments, and iliac and pubic crest. 

The abdominal muscles function as spinal flexors, rotators and lateral flexors, as well producing spinal stiffness and stability. The rectus abdominis is the primary spinal flexor owing to its attachments that extend across the middle of the abdomen, while the external oblique is the primary spinal rotator and lateral flexor.

The abdominals vary in size and weight, with the external oblique being the heaviest and the transverse abdominis being the lightest, at around half its weight. The muscle cross-sectional area of the abdominals also varies within each muscle, displaying considerable regional variation.


Top · Contents · References



 

MUSCLE ARCHITECTURE

[Read more: Muscle architecture]

PURPOSE

This purpose of this section is to provide a summary of the muscle architecture of the abdominal musculature.

 –

MUSCLE THICKNESS

Comparing the muscle thickness of the abdominal muscles, McGill et al. (1996) reported that external oblique thickness ranged between 7.4 – 9.7mm in males and 5.4 – 8.2mm in females. Average muscle thickness of the internal oblique ranged between 8.2 – 12.7mm in males and 7.4 – 9.6mm in females. Average muscle thickness of the transverse abdominis ranged between 4.4 – 5.1mm in males and 3.8 – 4.8mm in females. Teyhen et al. (2007) found that the relative thicknesses of the rectus abdominis, internal oblique, external oblique and transverse abdominis comprised 35%, 29%, 23% and 14% of the abdominal wall, respectively. Additionally, the thickness of the abdominal muscles appears to be unevenly distributed across the abdominal wall. The upper lateral portions are thicker than the middle and lower regions. Overall, the muscle thickness of the abdominals is generally greater in males compared to females and the internal oblique displays the largest difference between genders.

PENNATION ANGLE

The rectus abdominis displays the characteristics of a fusiform muscle, where the muscle fascicles extend the entire length of the muscle. Therefore, the pennation angle of the rectus abdominis is approximately 0 degrees (Delp et al. 2001). In contrast, the other abdominals are more pennated. Urquart et al. (2005) reported that the angles of the top, middle and lower regions of the transverse abdominis were 3, 13 and 21 degrees, respectively. In contrast, the top, middle and lower regions of the internal oblique were 48, 35, and 0 degrees, respectively. The top and middle regions of the external oblique were 49 and 59 degrees. Therefore, the transverse abdominis appears to be more heavily pennated in the lower abdomen, the internal oblique displays the opposite trend, and the external oblique is similarly pennated in both regions.

 –

FASCICLE LENGTH

Only a limited number of studies have assessed the fascicle length of the rectus abdominis. Delp et al. (2001) assessed the fascicle length in 5 cadavers aged 57 – 75 years. They reported that fascicle length was 283mm. Brown et al. (2011) reported the fascicle lengths for the external oblique, internal oblique and transverse abdominis, which measured 170, 79 and 95mm, respectively. The superficial abdominal muscles (rectus abdominis and external oblique) therefore display longer muscle fascicles compared with the deeper muscles.

PHYSIOLOGICAL CROSS-SECTIONAL AREA

Very few studies have assessed the physiological cross-sectional area (PCSA) of the rectus abdominis. Delp et al. (2001) assessed the PCSA in 5 cadavers aged 57 – 75 years. They reported that the PCSA measured 2.6cm2. Other studies have found larger PCSA values, ranging between 3.8 – 10.5cm2 (Reid et al. 1985; McGill et al. 1988; Chaffin et al. 1990). Differences between studies may be caused by different imaging techniques or different populations. Overall, PCSA of the rectus abdominis seems to range between 2.6 – 10.5cm2.

SECTION CONCLUSIONS

The abdominals vary in size and architecture. Additionally, aspects of muscle thickness and architecture vary along the length of each muscle. The rectus abdominis displays the greatest muscle thickness and longest muscle fascicles. The external oblique is most heavily pennated and the rectus abdominis is least pennated.


Top · Contents · References



MUSCLE FIBER TYPE

[Read more: Muscle fiber type]

PURPOSE

This section provides a summary of the muscle fiber type of the abdominal muscles.

BACKGROUND

Introduction

Knowledge of the muscle fiber type of the abdominals may be of interest to strength and conditioning coaches in order to tailor their resistance-training program accordingly, especially if muscle hypertrophy is important. Very little data exists assessing the fiber type distribution of the abdominals. Haggmark et al. (1979) found that the proportion of type I muscle fiber across the rectus abdominis, internal and external oblique was 55 – 58%, although there was considerable inter-individual variability.

SECTION CONCLUSIONS

The abdominals appear to display a mixed proportion of type I and type II muscle fibers, with type I muscle fiber ranging between 55 – 58% across the rectus abdominis, internal and external oblique muscles. This may imply that training with a mixture of both lighter and heavier loads is beneficial for this muscle.


Top · Contents · References



ELECTROMYOGRAPHY

[Read more: electromyography]

PURPOSE

This section provides a summary of the electromyography (EMG) activity studies into the abdominal muscles.

SECTION CONTENTS

  1. Comparison of compound exercises
  2. Comparison between upper and lower body exercises
  3. Comparison of upper body exercises
  4. The deadlift
  5. The squat
  6. Sit ups and curl ups
  7. Integrated core exercises
  8. Unstable, dynamic core exercises
  9. Isometric exercises

BACKGROUND

Introduction

Among sports scientists, it is widely accepted that electromyography (EMG) activity levels can provide a way for determining the best exercises for training a muscle. This is because EMG activity represents the extent to which the individual motor units within a muscle are active during a joint action. In non-fatigued muscles, the extent to which motor units are active determines the tensile force that is produced and this tensile force produces the mechanical loading that is thought to be one of the key drivers for long-term muscular adaptations (Schoenfeld, 2010).


 

COMPARISON OF COMPOUND EXERCISES

Introduction

Several studies have assessed muscle activity of the abdominals during compound exercises. The rectus abdominis and external oblique display moderate levels of muscle activity in the squat and deadlift but there is no difference in the levels of muscle activity between these lifts. Additionally, the rectus abdominis and external oblique display high levels of muscle activity during a number of less traditional compound exercises such as when strongman events like the tire flip, atlas stone lift, and shouldered keg walk. Furthermore, the rectus abdominis and external oblique muscle activity are highly active during upper body compound exercises. Nonetheless, it appears that isometric core exercises such as the plank, as well as dynamic abdominal exercises such as the straight-leg sit up, produce greater rectus abdominis muscle activity than many upper body and lower body compound exercises.

Comparison between back squat and deadlift

Comparing the squat and deadlift, Hamlyn et al. (2007) examined the external oblique muscle activity and the lower region of the deep abdominal (superior to inguinal ligament, medial to anterior superior iliac crest) muscle activity during the barbell back squat and conventional deadlift with 80% of 1RM. They reported no difference between the two exercises. Similarly, Willardson et al. (2009) reported that transverse abdominis, rectus abdominis and external oblique muscle activity levels were not different between the back squat and deadlift. Therefore, in practical terms both the squat and deadlift appear to produce similar muscle activity in the superficial and deep abdominals when performing the exercises with the same relative loads.

Comparison of one and two-handed kettlebell swings

RECTUS ABDOMINIS

Assessing the kettlebell swing, Andersen et al. (2015) measured the muscle activity of the rectus abdominis in the kettlebell swing with 1 and 2 hands. Using a 16kg kettlebell, they found that lower and upper rectus abdominis muscle activity ranged between 18 – 45% and 11 – 19% of maximum voluntary isometric contraction (MVIC) levels, respectively. Rectus abdominis muscle activity tended to be greater during the hip extension (upward) phase compared to the hip flexion (downward) phase. Additionally, rectus abdominis displayed superior muscle activity in the same (ipsilateral) side as the kettlebell during both the bottom and top half of the movement compared to the contralateral (opposite) side. The rectus abdominis muscle activity in the ipsilateral side was no different to the two-handed swing in any phase on the movement. Therefore, there seems to be no benefit to the rectus abdominis when training the one-handed kettlebell swing instead of the two-handed variation.

EXTERNAL OBLIQUE

Assessing the kettlebell swing, Andersen et al. (2015) measured the muscle activity of the external oblique in the kettlebell swing with 1 and 2 hands. Using a 16kg kettlebell, they found no difference between phases or conditions.

 

Comparison between strongman exercises

RECTUS ABDOMINIS

Exploring strongman type exercises, McGill et al. (2009) measured rectus abdominis muscle activity in a number of exercises including the farmer’s walk, suitcase carry, super yoke walk, tire-flip, and shouldered keg walk. They reported that rectus abdominis muscle activity was highest in the tire flip (69 – 87% of MVIC) and atlas stone lift (76 – 77% of MVIC).

EXTERNAL OBLIQUE

Exploring strongman type exercises, McGill et al. (2009) measured external oblique muscle activity in a number of exercises including the farmer’s walk, suitcase carry, super yoke walk, tire-flip, and shouldered keg walk. The external oblique displayed its greatest muscle activity during the atlas stone lift (97 – 103% of MVIC), tire flip (80 – 106% of MVIC) and shouldered keg walk (39 – 87% of MVIC).

Comparison between back squat and sled apparatus

Comparing the back squat and the sled push, Maddigan et al. (2014) measured transverse abdominis and internal oblique muscle activity in the back squat performed with 10RM and the weighted sled push performed with a 20 step maximum. Transverse abdominis and internal oblique muscle activity were not different between two exercises.

Effect of surface stability

Assessing the effect of surface stability, Wahl et al. (2005) compared the muscle activity of the abdominals during a number of unloaded lower body exercises performed in stable environments (on the floor) and in unstable environments, using an inflatable disc. The exercises included the static font lunge, side lunge, calf raises, and single leg hip extension. Rectus abdominis muscle activity was not different between the stable and unstable conditions. Additionally, Willardson et al. (2009) compared exercises performed stable environments (on the floor) and in unstable environments, using a BOSU ball. The exercises were the deadlift and back squat with 50% of 1RM. There were no differences between the exercises between the stable and unstable conditions. Using unstable surfaces with low or moderate relative loads therefore seems to have no benefit for the rectus abdominis.

Summary

The rectus abdominis and external oblique display moderate levels of muscle activity during squat and deadlift variations, but there is no difference in muscle activity of the abdominals between the squat and deadlift. They are highly active during less traditional, compound exercises such as the strongman tire flip, atlas stone lift and shouldered keg walk.

Back to top of page · Back to top of section · Down to references



 

COMPARISON BETWEEN UPPER AND LOWER BODY EXERCISES

Comparison between compound exercises

RECTUS ABDOMINIS

Comparing compound exercises, Comfort et al. (2011) explored the rectus abdominis muscle activity in the back squat, front squat and the standing barbell overhead press with a load of 40kg. Rectus abdominis muscle activity tended to be greater in the standing barbell overhead press compared to the front and back squat with the same absolute load. However, the load used in this study may not reflect the load used during the squat and deadlift in resistance training programs. Willardson et al. (2009) compared the back squat, conventional deadlift, barbell curl, and standing barbell press performed with 50% and 75% of 1RM. They also reported that rectus abdominis muscle activity was superior when performing the overhead press compared to the back squat, deadlift and curl. Therefore, it appears that the standing barbell overhead press produces higher levels of rectus abdominis muscle activity than the squat or deadlift exercises.

EXTERNAL OBLIQUE

Comparing compound exercises, Willardson et al. (2009) compared the back squat, conventional deadlift, barbell curl, and standing barbell press performed with 50% and 75% of 1RM. They reported that external oblique muscle activity was superior when performing the standing barbell overhead press compared to the back squat, deadlift and curl.

Comparison between compound and plank exercises

RECTUS ABDOMINIS

Comparing compound exercises to the plank, Aspe et al. (2014) investigated rectus abdominis muscle activity during the back squat and overhead squat with 90% of 3RM and in the front plank and side plank. The front plank tended to display the greatest rectus abdominis muscle activity. Comfort et al. (2011) also reported greater rectus abdominis muscle activity in the front plank compared to the front squat and back squat performed with an absolute load of 40kg. In contrast, Hamlyn et al. (2007) found that the lower region of the deep abdominals muscle activity was no different between the side plank, back squat and deadlift performed with 80% of 1RM. Overall, it seems that the front plank displays superior rectus abdominis muscle activity to the back squat and overhead squat.

EXTERNAL OBLIQUE

Comparing compound exercises to the plank, Aspe et al. (2014) investigated external oblique muscle activity during the back squat and overhead squat with 90% of 3RM and in the front plank and side plank. External oblique muscle activity was higher in the front and side plank compared to the back squat and overhead squat.

Comparison between compound and trunk flexion exercises

RECTUS ABDOMINIS

Comparing compound exercises and trunk flexion exercises, Aspe et al. (2014) explored rectus abdominis muscle activity in a number of exercises including the front and overhead squat performed with 90% of 3RM, as well as the swiss ball jack knife and straight-leg sit up. Rectus abdominis muscle activity was highest in the straight-leg sit up. Rectus abdominis muscle activity was higher in the straight-leg sit up and Swiss ball jack knife than in either the back squat or overhead squat. In contrast, Hamlyn et al. (2007) found no difference in the deep abdominal muscles (measured in the lower abdomen) muscle activity between the superman (prone trunk extension), back squat and deadlift, where the back squat and deadlift were performed with 80% of 1RM.

EXTERNAL OBLIQUE

Comparing compound exercises and trunk flexion exercises, Aspe et al. (2014) explored external oblique muscle activity in a number of exercises including the front and overhead squat performed with 90% of 3RM, as well as the Swiss ball prone jack knife and straight-leg sit up. The straight-leg sit up and swiss ball jack knife displayed greater external oblique muscle activity than the back squat and overhead squat. In contrast, Hamlyn et al. (2007) found that the external oblique muscle activity was no different between the superman (prone trunk extension) exercise when compared to the back squat and deadlift, where the back squat and deadlift were performed with 80% of 1RM.

Effect of stability at the hand or foot

Assessing the effect of stability during both compound and trunk flexion exercises, Mok et al. (2014) assessed the muscle activity of the abdominals in a number of suspension exercises including the hip abduction plank (feet in straps), press up, inverted row and hamstring curl (feet in straps). During the hip abduction plank, the external oblique displayed greater muscle activity than the rectus abdominis but there was no difference between the muscle activity of the rectus abdominis and the external oblique during the press up. Only the external oblique in hip abduction plank displayed levels of muscle activity considered high, suggesting that suspension exercises may not be beneficial for training the abdominals.

Summary

Rectus abdominis and external oblique muscle activity levels are both greater in the standing overhead press, plank, and Swiss ball jack knife compared to the squat and deadlift.

Despite the popularity of unstable surface training for developing the trunk musculature, many unstable multi-joint exercises do not produce superior muscle activity compared to their stable equivalents.

Back to top of page · Back to top of section · Down to references



COMPARISON OF UPPER BODY EXERCISES

Comparison between pressing variations

Comparing the effect of exercise variation, Santana et al. (2007) explored the muscle activity of the abdominals during the bench press and standing single-arm cable press with similar relative loads. They reported superior rectus abdominis muscle activity in the contralateral (opposite) side when performing the standing cable press compared with the bench press. In practical terms, the standing single arm horizontal press may therefore be a suitable integrated core exercise.

Comparison between rowing variations

Comparing the effect of rowing exercise variation, Fenwick et al. (2009) assessed rectus abdominis and external oblique muscle activity during the inverted row, barbell bent-over row, and standing single-arm cable row. Muscle activity was very low in both muscles in all exercises but the external oblique displayed greatest muscle activity in the standing single-arm cable row. Importantly, in this study the researchers matched the loading between exercises relative to the inverted row (mass of individual e.g. 100kg – mass of individual when performing inverted row) and not by using the same relative load, so it is unclear whether differences would arise when using the same relative loads.

Comparison between vertical pulling variations

Comparing vertical pulling variations, McGill et al. (2014) reported a trend towards superior rectus abdominis muscle activity in the chin up compared to the pull up. Youdas et al. (2010) found no difference in external oblique muscle activity between the chin up, pull up and rotating handle pull up and external oblique muscle activity was relatively in all exercises.

Effect of surface stability during horizontal pressing

Exploring the effect of stability on muscle activity of the abdominals, Marshall et al. (2005) compared the push up exercise on a stable surface (floor) to the unstable swiss ball. They report greater rectus abdominis and transverse abdominis muscle activity at the top position of a press up performed on the Swiss ball, while no difference was found at the bottom position. Lehman et al. (2005) compared the press up performed with either the hands or feet on a stable surface (bench) or on a Swiss ball. They found no difference in rectus abdominis muscle activity between stable and unstable conditions. These findings indicate that stability during horizontal pressing does not affect muscle activity of the abdominals.

Effect of stability during the bench press

[Read more: bench press]

RECTUS ABDOMINIS

Exploring the effect of stability in the bench press, Saeterbakken et al. (2013) compared the bench press performed on a stable bench, a balance cushion and a Swiss ball, with 6RM. Rectus abdominis muscle activity was higher when using the Swiss ball compared to all other conditions. Goodman et al. (2008) compared the bench press performed on a stable bench and a Swiss ball, with 1RM but found no difference in rectus abdominis muscle activity between conditions. Norwood et al. (2007) compared the bench press performed with varying degrees of instability (bench, feet on a BOSU ball, the upper body on a Swiss ball, both feet on a BOSU ball and upper body on a Swiss ball). There was no difference in rectus abdominis muscle activity between conditions but the same absolute load of 9.1kg was used for all conditions. Overall, performing the bench press under unstable conditions appears to produce superior rectus abdominis muscle activity.

EXTERNAL OBLIQUE

Goodman et al. (2008) compared the bench press performed on a stable bench and a Swiss ball, with 1RM and found no difference in external oblique muscle activity between the conditions. Saeterbakken et al. (2013) compared the bench press performed on a stable bench, a balance cushion and a Swiss ball, with 6RM. They also reported that external oblique muscle activity was no different between the conditions. Performing the bench press under unstable conditions does not appear to affect external oblique muscle activity.

 

Transverse abdominis and internal oblique

Assessing the effect of surface stability, Norwood et al. (2007) compared the bench press performed with varying degrees of instability (bench, feet on a BOSU ball, the upper body on a Swiss ball, both feet on a BOSU ball and upper body on a Swiss ball). They reported that internal oblique muscle activity was highest with either lower body instability (feet on BOSU) or combined upper body and lower body instability (BOSU and swiss ball) but the same absolute load of 9.1kg was used for all conditions.

Effect of surface stability during seated vertical pressing

RECTUS ABDOMINIS

Assessing the effect of stability during seated vertical pressing, Kohler et al. (2010) compared the seated overhead press with dumbbells or a barbell and with either a stable surface (bench) or an unstable surface (a Swiss ball). Rectus abdominis muscle activity was higher in the seated overhead press on a bench than on the Swiss ball, with either a barbell or dumbbell. Performing the seated press using a stable bench would seem to be optimal for the rectus abdominis.

EXTERNAL OBLIQUE

Assessing the effect of stability during seated vertical pressing, Kohler et al. (2010) compared the seated overhead press with dumbbells or a barbell and with either a stable surface (bench) or an unstable surface (a Swiss ball). External oblique muscle activity was higher with a barbell compared to dumbbells (when using a bench), as well as on a bench compared to a Swiss ball. Performing the seated press with a barbell and using a stable bench would seem to be optimal for the external oblique.

Effect of stability at the hand

Exploring stability at the hand, Maeo et al. (2014) compared muscle activity of the abdominals when performing the push up with the hands on the ground or using suspension system handles. They found that rectus abdominis, external oblique and internal oblique muscle activity levels were all higher when utilising the suspension push up compared to the push up on the ground. Furthermore, rectus abdominis displayed the highest muscle activity of all the abdominal muscles but still only reached 45% of MVIC, which may indicate that muscle activity is insufficient to provide a training effect during this exercise.

Summary

Rectus abdominis muscle activity is higher in the standing horizontal press compared to the barbell bench press, while performing the seated overhead press and bench press on unstable surfaces do not appear to be beneficial. The rectus abdominis and external oblique appear to display high levels of muscle activity during vertical pressing and pulling.

Back to top of page · Back to top of section · Down to references



THE DEADLIFT

[Read more: deadlift]

Introduction

The deadlift produces moderate levels of rectus abdominis and external muscle activity. Training with a weightlifting belt increases rectus abdominis muscle activity but reduces external oblique muscle activity. The lifting phase of the deadlift involves the greatest muscle activity of the abdominals but surface instability has no effect.

Comparison between conventional and sumo deadlift

Assessing exercise technique in the deadlift, Escamilla et al. (2002) examined rectus abdominis and external oblique muscle activity. They found that muscle activity ranged between 56 – 60% of MVIC in the two muscles but there was no difference between the two deadlift techniques for either muscle. Additionally, the level of muscle activity was moderate in both muscles, suggesting that the deadlift might be a useful exercise for training the abdominals.

Comparison between phases

Comparing between the phases of the deadlift, Escamilla et al. (2002) found that muscle activity of the abdominals was greater in the lifting phase compared to the lowering phase for the rectus abdominis (65 – 80% of MVIC) and for the external oblique (66 – 75% of MVIC), regardless of deadlift variation.

Effect of knee joint angle 

RECTUS ABDOMINIS

Comparing different knee joint angles in the deadlift, Escamilla et al. (2002) explored the muscle activity of the abdominals at knee joint angles of: 90 – 61 degrees (lift-off position), 60 – 31 degrees (mid-range), and 30 – 0 degrees (lock-out). They reported that rectus abdominis muscle activity was higher at 60 – 31 degrees compared to at 90 – 61 degrees during the lifting phase. Rectus abdominis muscle activity was highest at knee flexion angles of 60 – 31 degrees in the lowering phase. Rectus abdominis muscle activity is therefore highest in the first part of the lifting phase and the middle part of the lowering phase.                                                                                                                                                  

EXTERNAL OBLIQUE

Comparing different knee joint angles in the deadlift, Escamilla et al. (2002) explored the muscle activity of the abdominals at knee joint angles of: 90 – 61 degrees (lift-off position), 60 – 31 degrees (mid-range), and 30 – 0 degrees (lock-out). The external oblique displayed similar muscle activity levels across the whole of the lifting phase. In the lowering phase, external oblique muscle activity was greatest at knee flexion angles of 60 – 31. External oblique muscle activity is therefore similarly active across the whole of the lifting phase and highest in the middle part of the lowering phase.

Effect of equipment

RECTUS ABDOMINIS

Assessing the effect of equipment, Escamilla et al. (2002) explored the muscle activity of the abdominals during conventional and sumo deadlifts with and without a weightlifting belt. They reported that rectus abdominis muscle activity was greater when using a weightlifting belt compared to without a weightlifting belt in both the conventional or sumo deadlift.

EXTERNAL OBLIQUE

Assessing the effect of equipment, Escamilla et al. (2002) explored the muscle activity of the abdominals during conventional and sumo deadlifts with and without a weightlifting belt. They reported that the external oblique displayed greater muscle activity when performing the deadlift without a belt in both the conventional or sumo deadlift, which is the opposite of the rectus abdominis.

Assessing surface stability during the deadlift

Assessing the effect of surface stability, Willardson et al. (2009) explored the muscle activity of the abdominals when performing the conventional deadlift with a stable base (at 50% and 75% of 1RM) and when standing on a BOSU ball (50% of 1RM). They reported that rectus abdominis, external oblique and transverse abdominis muscle activity did not differ between stable and unstable conditions.

Summary

During deadlifts, rectus abdominis or external oblique muscle activity is moderate, indicating that it may be a useful exercise for the abdominals. Exercise technique (conventional or sumo) does not affect rectus abdominis or external oblique muscle activity, but muscle activity is greater in the ascending phase than in the descending phase. Surface stability in the deadlift does not affect muscle activity of the abdominals.

Back to top of page · Back to top of section · Down to references



THE SQUAT

[Read more: squat]

Introduction

Several studies have explored the trunk muscle activity during the squat. Overall, training with moderate to high relative loads appears to produce moderate levels of muscle activity in the abdominals. Using free weight or machine-type load, utilising attentional focus, a weightlifting belt or unstable surfaces appears to have little or no additional benefit. Of the exercise variations, the overhead squat appears to produce very high levels of rectus abdominis muscle activity.

Effect of relative load

RECTUS ABDOMINIS

Several studies have investigated the effect of relative load on rectus abdominis muscle activity. Bressel et al. (2009) explored rectus abdominis muscle activity in the back squat with low (50% of 1RM) and high (75% of 1RM) relative loads. The researchers reported that rectus abdominis muscle activity did not differ between low or high relative loads. Willardson et al. (2009) also found no difference in rectus abdominis muscle activity between the back squat performed with 50% and 75% of 1RM. And Aspe et al. (2014) found that rectus abdominis muscle activity did not differ between relative loads of 60, 75 and 90% of 3RM. Therefore, rectus abdominis muscle activity does not change with increasing relative load in the squat.

EXTERNAL OBLIQUE 

Several studies have investigated the effect of relative load on external oblique muscle activity. Bressel et al. (2009) explored external oblique muscle activity in the back squat with low (50% of 1RM) and high (75% of 1RM) relative loads. They reported that external oblique muscle activity was higher with greater relative loads. Similarly comparing 50% and 75% of 1RM, Willardson et al. (2009) also found that external oblique muscle activity was higher with greater relative loads. However, Aspe et al. (2014) found that external oblique muscle activity did not differ between relative loads of 60, 75 and 90% of 3RM. Overall, the external oblique muscle activity seems to increase with increasing relative load.                           

TRANSVERSE ABDOMINIS

Several studies have investigated the effect of relative load on transverse abdominis muscle activity. Willardson et al. (2009) explored transverse abdominis muscle activity during back squats with 50% and 75% of 1RM and found no differences between relative loads. Therefore, transverse abdominis muscle activity does not change with increasing relative load in the squat.

Comparison between front and back squats 

Comparing barbell squat variations, Comfort et al. (2011) explored rectus abdominis muscle activity in the front and back squats with 40kg and found no difference between exercises. However, the same relative load was not used in both cases and different results might be observed if this comparison was investigated.

Comparison between back and overhead squats

Comparing barbell squat variations, Aspe et al. (2014) explored the muscle activity of the abdominals during back squats and overhead squats with 60, 75 and 90% of 3RM. Rectus abdominis and external oblique muscle activity were higher in the overhead squat compared to the back squat. Even so, the size of the difference in muscle activity was very small (at between 2 – 7%). In practical terms, the back and overhead squat may therefore provide similar training effects for the abdominal muscles.

Comparison between barbell and machine squats

Comparing barbell and machine squats, Schwanbeck et al. (2009) explored rectus abdominis and transverse abdominis muscle activity in the back squat with either a barbell or using a smith machine, with 8RM. There was no difference between conditions in either muscle. Similarly, Andersen et al. (2005) found that muscle activity of the deep abdominal stabilisers was similar in barbell back squats and smith machine squats with the same absolute. Therefore, despite common claims to the contrary, muscle activity of the abdominals seems to be challenged equally during the back squat and the machine squat.

Comparison between one and two-legged squats

Comparing squat variations, Andersen et al. (2014) explored rectus abdominis and external oblique muscle activity in the back squat and split squat, with 6RM. They found no difference in rectus abdominis muscle activity between exercises. However, they noted superior external oblique muscle activity when performing the split squat compared to the back squat. Therefore, despite common claims to the contrary, muscle activity of the rectus abdominis seems to be challenged equally during the back squat and the split squat.

Effect of attentional focus

Assessing the effect of attentional focus, Bressel et al. (2009) explored muscle activity of the rectus abdominis, internal and external oblique, and transverse abdominis, during back squats with 50% of 1RM without verbal instruction, and then followed by an internal cue focusing on bracing the trunk. They reported that internal cues led to higher transverse abdominis muscle activity and higher external oblique muscle activity compared to no internal cues. Furthermore, rectus abdominis, external and internal oblique muscle activity was superior when performing the back squat following the internal cue compared with performing the back squat on an unstable surface (a BOSU ball). Therefore, an internal cue to brace the trunk appears to be a better method of increasing trunk muscle activity in the back squat than the more traditional method of using unstable surfaces.

Effect of equipment

Assessing the effect of equipment, Lander et al. (1990) explored rectus abdominis muscle activity during back squats with or without two types of weightlifting belt, with 90% of 1RM. They reported that rectus abdominis muscle activity was not affected by the use of the weightlifting belts.

Effect of external resistance type

Assessing the effect of external resistance, Saeterbakken et al. (2014) explored muscle activity of the abdominals during the back squat with either a barbell or a combination of a barbell and elastic resistance (where elastic resistance comprised between 25 – 40% total load, depending on the phase of the lift), using 6RM. They reported that there was no difference in rectus abdominis muscle activity or in external oblique muscle activity between conditions.

Effect of surface stability in back squats

RECTUS ABDOMINIS

Assessing the effect of surface stability, Bressel et al. (2009) explored muscle activity of the abdominals during the barbell back squat in stable (on the floor) and unstable  (on a BOSU ball) conditions. They reported that rectus abdominis muscle activity was not different between the conditions. Additionally, Willardson et al. (2009) compared the back squat with 50 and 75% relative loads on stable surfaces, and 50% relative load utilising a BOSU ball. They found no difference in rectus abdominis muscle activity between conditions.

EXTERNAL OBLIQUE

Assessing the effect of surface stability, Bressel et al. (2009) compared muscle activity of the abdominals during the back squat with relative loads of 50 and 75% on stable surfaces, and with a BOSU ball with 50% of 1RM. They reported higher external oblique muscle activity with the BOSU ball at 50% of 1RM compared to the stable condition, but no difference between the BOSU ball and 75% of 1RM conditions. Additionally, Willardson et al. (2009) found similar results insofar that the external oblique displayed similar muscle activity between the stable (50% and 75% of 1RM) and 50% of 1RM BOSU condition.

TRANSVERSE ABDOMINIS

Assessing the effect of surface stability, Willardson et al (2009) found no difference in transverse abdominis muscle activity between stable (50% and 75% of 1RM) and unstable (50% of 1RM BOSU) conditions. Similarly, Bressel et al. (2009) also found no difference between conditions. Using an unstable surface does not appear to affect transverse abdominis muscle activity during squats.

Effect of surface stability in split squats

Assessing the effects of surface stability in split squats, Andersen et al. (2014) explored rectus abdominis muscle activity in the split squat in stable (on the floor) or unstable (on a foam cushion) conditions, with 6RM. There was no difference in rectus abdominis muscle activity between conditions.

Summary 

During the squat, increasing relative load leads to greater external oblique muscle activity but does not alter rectus abdominis or transverse abdominis muscle activity. Muscle activity of the abdominals appears to be similar across almost all possible squat variations (back, front overhead, machine, and elastic band-resisted), although the external oblique may display greater muscle activity in the split squat than in the back squat.

During the squat, internal cues seem to produce greater transverse abdominis muscle activity and higher external oblique muscle activity than no internal cues. In contrast, using a weightlifting belt and using unstable surfaces have no effect on the muscle activity of the abdominals.

Back to top of page · Back to top of section · Down to references



SIT UPS AND CURL UPS

Introduction

Sit ups are a traditional callisthenic exercise that has been used for many years to develop the muscular endurance of the abdominals. Sit ups involve dynamic hip flexion and also either isometric or dynamic trunk flexion, depending on the technique used. Sit ups can be performed with either anchored or unanchored feet and with either bent legs or straight legs. A variation on the sit up that only involves trunk flexion and does not involve hip flexion is known as the curl up or crunch. Again, the curl up can be performed with either bent legs or straight legs.

Effect of adding external load

Assessing the effect of relative load during different trunk flexion exercises, Sternlicht et al. (2003) compared a number of abdominal exercises (Ab Roller Plus, Torso Track 2, AB-Doer Pro, and the Perfect Abs) to the traditional curl up. They found increased rectus abdominis muscle activity when performing trunk flexion exercises with added elastic resistance from a portable device (Perfect Abs). Additionally, greater external resistance (thicker bands) led to greater rectus abdominis muscle activity and greater external oblique muscle activity.

Effect of range of motion

Assessing the effect of joint range of motion (ROM), Andersen et al. (1997) compared rectus abdominis muscle activity between sit ups performed with trunk flexion (at the lumbar spine) with sit ups performed with hip flexion. Rectus abdominis muscle activity increased with increasing trunk flexion angles during the trunk flexion sit up but decreased with increasing hip flexion angles during the hip flexion sit up. In practical terms, rectus abdominis muscle activity may be maximised by favouring the top portion of the trunk flexion sit up (also called curl ups or crunches) and the bottom and middle portions of the hip flexion sit-up.

Comparison between anchored and unanchored exercises

Assessing the effect of anchoring the feet, Andersson et al. (1997) compared the straight-legged curl up and straight-legged sit up with and without the feet anchored to the floor. There was no difference between the two exercises or between the anchored and unanchored trunk flexion exercises.

Comparison between sit up techniques

RECTUS ABDOMINIS

Assessing the effect of sit up technique, Andersson et al. (1997) measured rectus abdominis muscle activity when performing the curl up (trunk flexion only), sit up (hip flexion only), and spontaneous sit up (both trunk and hip flexion) with either straight or bent legs, and either anchored or unanchored. Rectus abdominis average muscle activity ranged between 60 – 80% of MVC during all exercise conditions. Generally, the rectus abdominis muscle activity was greater when performing the curl up or sit up with straight legs anchored or unanchored compared to the bent leg curl up or sit up, however no difference were reported. Additionally, Konrad et al. (2001) found no difference in rectus abdominis muscle activity between the curl up with the hips and knees at 90 degrees of flexion, feet resting on a bench, and the bent leg unanchored sit up. Therefore, it appears that the rectus abdominis produces similar muscle activity between the curl up and sit up.

EXTERNAL OBLIQUE

Assessing the effect of sit up technique, Andersson et al. (1997) compared the external oblique muscle activity between the trunk flexion sit up, hip flexion sit up, or spontaneous sit up (both trunk and hip flexion) with both straight and bent legs. External oblique average muscle activity ranged between 75 – 85% in the sit up and spontaneous sit up conditions, compared to 15 – 25% during the curl up conditions. They found that external oblique muscle activity was lower in the curl up than both the sit up and spontaneous sit up. Konrad et al. (2001) also found that external oblique muscle activity was superior in the sit up compared with the curl up. It appears that the involvement of hip flexion increases external oblique muscle activity during the sit up, when performed with either straight or bent legs.

Comparison between curl up variations

RECTUS ABDOMINIS

Comparing curl up variations, Konrad et al. (2001) explored the muscle activity of the rectus abdominis during the bent leg curl up with and without trunk rotation. Rectus abdominis muscle activity was not different between conditions. Whiting et al. (1999) compared curl up variations including the curl up with arms overhead, arms down, the cross curl-up (oblique curl), and reverse curl up. They found no difference in rectus abdominis muscle activity between the curl up variations.

EXTERNAL OBLIQUE

Comparing curl up variations, Konrad et al. (2001) measured external oblique muscle activity during the bent leg curl up with and without trunk rotation. External oblique muscle activity was higher in the bent leg curl up with combined trunk rotation compared to the bent leg curl up without combined trunk rotation. Adding trunk rotation therefore appears to increase external oblique muscle activity during the curl up.

Effect of trunk flexion or pelvic tilt

Comparing the curl up and the posterior pelvic tilt exercise, Sarti et al. (1996) measured rectus abdominis muscle activity. Interestingly, the curl up produced greater upper rectus abdominis muscle activity, while the posterior tilt exercise displayed superior lower rectus abdominis muscle activity. However, in a similar study in which the reverse curl was compared with the curl, up, Whiting et al. (1999) compared the curl up to the reverse curl up and reported no difference in rectus abdominis muscle activity.

Effect of unstable surfaces

RECTUS ABDOMINIS

Assessing the effect of surface stability, Vera-Garcia et al. (2000) explored rectus abdominis muscle activity during the curl up on stable (on the floor) or unstable (on a Swiss ball) surfaces. Rectus abdominis muscle activity was higher in the curl up on a Swiss ball than on the floor. Imai et al. (2010) measured rectus abdominis muscle activity during the bent leg curl up on stable (on the floor) and unstable (on a Swiss ball) surfaces but there was no difference between conditions. Duncan et al. (2009) measured rectus abdominis muscle activity during the bent leg curl on stable (on the floor) and unstable (on a Swiss ball) surfaces. Rectus abdominis muscle activity was higher in the curl up on a Swiss ball than on the floor. Overall, using an unstable surface may increase rectus abdominis muscle activity.

EXTERNAL OBLIQUE

Assessing the effect of surface stability, Imai et al. (2010) measured external oblique muscle activity during the bent leg curl up on stable (on the floor) and unstable (on a Swiss ball) surfaces. External oblique muscle activity was higher in the curl up on a Swiss ball than on the floor. Overall, using an unstable surface may increase external oblique muscle activity.

Effect of attentional focus

Assessing the effect of altering attentional focus, Karst et al. (2004) explored muscle activity of the abdominals when performing the curl up with and without internal cues to activate either the rectus abdominis or the external oblique. They reported that the internal cue for the external oblique produced higher external oblique muscle activity but lower rectus abdominis muscle activity. In contrast, using internal cues for the rectus abdominis muscle activity did not affect either rectus abdominis external oblique muscle activity. Sullivan et al. (2015) also studied the effect of internal cues by having subjects focus on slowly and actively shortening and contracting the rectus abdominis and external oblique during a bent leg sit up. Compared to the normal bent knee sit up, the internal cues resulted in higher rectus abdominis but the external oblique displayed lower muscle activity, possibly due to increased attention to trunk flexion.

Comparison with other isolated core exercises

RECTUS ABDOMINIS

Comparing different core isolation exercises, Youdas et al. (2008) measured rectus abdominis muscle activity in the ab roll out, bent-leg curl up, supine double-leg lowering, and side bridge. Rectus abdominis muscle activity was highest in the ab roll out and lowest in the side bridge. Similarly, Aspe et al. (2014) compared the front plank, side plank, Swiss-ball jack knife, and straight-leg sit up. Rectus abdominis muscle activity was highest when performing the straight-leg sit up compared with all other exercises. Konrad et al. (2001) reported that the reverse crunch displayed higher rectus abdominis muscle activity compared to the curl up, sit up, and decline curl up. Additionally, Hildenbrand et al. (2004) reported that rectus abdominis muscle activity was higher in the bent-leg, unsupported curl up, Swiss ball curl up, and the Ab-Roller curl up device compared to Ab Slide roll out. Escamilla et al. (2006) compared the power wheel roll out (power wheel in hands), jack knife and knee-tuck (power wheel attached to feet), the ab sling bent-leg hanging leg raise, the flat and decline reverse curl up, the anchored bent leg sit up, and bent leg curl up. They report that upper and lower rectus abdominis muscle activity ranged between 39 – 76% and 38 – 81% of MVIC. Further, upper rectus abdominis muscle activity was highest in the roll out, bent-leg hanging leg raise, and decline reverse crunch. Lower rectus abdominis muscle activity was highest in the roll out and bent-leg hanging leg raise.

EXTERNAL OBLIQUE

Comparing different core isolation exercises, Youdas et al. (2008) measured external oblique muscle activity during the kneeling roll out, bent leg curl up, supine double leg lowering, and side bridge. External oblique muscle activity was highest during supine double leg lowering and lowest in the side bridge. Hildenbrand et al. (2004) found that external oblique muscle activity was higher in the kneeling roll out than during bent-leg, unsupported curl ups, Swiss ball curl ups, and the Ab-Roller curl up device. Konrad et al. (2001) compared a number of gymnastic exercises and found that the horizontal straight leg anchored side bend displayed the highest external oblique muscle activity, followed by the reverse curl up Escamilla et al. (2006) compared the power wheel roll out (power wheel in hands), jack knife and knee-tuck (power wheel attached to feet), the ab sling bent-leg hanging leg raise, the flat and decline reverse curl up, the anchored bent leg sit up, and bent leg curl up. They report that the external oblique muscle activity ranged between 27 – 96% of MVIC. External oblique muscle activity was highest in the power wheel jack knife, knee-tucks and ab sling bent leg hanging raise.

INTERNAL OBLIQUE

Comparing different core isolation exercises, Youdas et al. (2008) measured internal oblique muscle activity during the roll out, bent leg curl up, supine double leg lowering, and side bride. Internal oblique muscle activity was highest during the roll out and lowest during the side bridge. Therefore, the roll out may be one of the most beneficial exercises for training the internal oblique.

Summary

Sit ups (hip flexion with or without trunk flexion) can be performed with either anchored or unanchored feet and with either bent legs or straight legs. A variation on the sit up that only involves trunk flexion and does not involve hip flexion is known as the curl up or crunch. The curl up can also be performed with either bent legs or straight legs.

Rectus abdominis muscle activity is similar in sit ups and curl ups but external oblique muscle activity is higher in sit ups than curls ups. Rectus abdominis muscle activity is similar in all curl up variations. External oblique muscle activity is highest in the curl up variation with trunk rotation.

Adding external load and using an unstable surface during curl ups leads to greater rectus abdominis and external oblique muscle activity. Using internal cues to focus on the muscle does not improve rectus abdominis muscle activity but leads to preferentially more external oblique muscle activity. 

Rectus abdominis muscle activity is higher when performing the kneeling roll out, hanging leg raises and in some cases the reverse curl up compared to sit up and curl up exercises. External oblique muscle activity is higher during a number of dynamic isolation exercises compared to the sit up and curl up including the kneeling roll out, horizontal side bend, jack knife, hanging leg raise.

Back to top of page · Back to top of section · Down to references



INTEGRATED CORE EXERCISES

Introduction

Integrated and whole-body linkage exercises are typically utilised in athletic populations and aimed at improving the ability to transmit force through the body and across the trunk. Integrated and whole body linkage exercises require the abdominal muscles to display high levels of muscle activity to produce a stiffened and stabilised torso (McGill et al. 2014).    Some studies have assessed a number of integrated core or whole-body linkage exercises that challenge spinal stability and force transmission through the body. Typically, these exercises include movement of distal segments such as the the shoulder or lower limbs or changes in body position that increase the moment arm about the trunk.

Comparison between whole-body linkage exercises

RECTUS ABDOMINIS

Assessing different whole-body linkage exercises, McGill et al. (2014) explored muscle activity of the abdominals during the hanging leg raise (straight-leg and bent-leg variations), hand walk-out and body-saw in a suspension system. Rectus abdominis muscle activity was very high, ranging between 70 – 130% of MVIC. Rectus abdominis muscle activity was highest during straight-leg hanging leg raises and lowest in bent-leg hanging leg raises. Additionally, Gotschall et al. (2013) compared the curl up with bent legs to a number of whole-body linkage exercises including the single arm supported plank with arm reach, side plank with arm raised, and mountain climber plank. The plank with arm reach, side plank with arm reach, and mountain climber plank all produced higher rectus abdominis muscle activity compared to the curl up exercise.

EXTERNAL OBLIQUE

Assessing different whole-body linkage exercises, McGill et al. (2014) muscle activity of the abdominals during the hanging leg raise (straight-leg and bent-leg variations), hand walk-out and body-saw in a suspension system. External oblique muscle activity ranged between 41 – 87% of MVIC and was greatest in straight-leg hanging leg raises and lowest in bent-leg hanging leg raises. Gotschall et al. (2013) compared the curl up with bent legs to a number of whole-body linkage exercises including the single arm supported plank with arm reach, side plank with arm raised, and mountain climber plank. The plank with arm reach, side plank with arm reach, and the birddog with elastic resistance produced greater external oblique muscle activity compared to the curl up with bent legs.

INTERNAL OBLIQUE

Assessing different whole-body linkage exercises, McGill et al. (2014) muscle activity of the abdominals during the hanging leg raise (straight-leg and bent-leg variations), hand walk-out and body-saw in a suspension system. Internal oblique muscle activity ranged between 24 – 52% of MVIC and was greatest in the straight-leg hanging leg raise and lowest in the body-saw exercise.

Summary

Integrated core exercise, including whole-body linkage and dynamic stabilisation exercises, are commonly-used for developing the abdominals. However, only the plank with arm reach and side plank with arm reach can outperform traditional curl ups for rectus abdominis and external oblique muscle activity.

Back to top of page · Back to top of section · Down to references



UNSTABLE SURFACE DYNAMIC CORE EXERCISES

Introduction

Exercises performed on unstable surfaces are utilised typically due to the role of the abdominals as spinal stabilisers and the exercises inherent degrees of freedom. Unstable surfaces can be utilised with a plethora of dynamic core exercises and are classically positioned under the trunk or feet to perform the curl up, sit up or spinal flexion exercises. A popular unstable device is the Swiss ball, an inflatable rubber ball that is weight bearing. The Swiss ball can be used for many traditional abdominal exercises, and integrated core exercises.

Comparison between Swiss ball exercises

Comparing Swiss ball exercises, Marshall et al. (2010) assessed rectus abdominis muscle activity during the plank with arms on the Swiss ball, single-leg hip hyperextension from the push up position with legs on the Swiss ball, single-leg squat against a wall on a Swiss ball, Swiss ball roll outs, and Swiss ball full body rolls from a supine bent leg start position with the upper back on the ball, and rotating 90 degrees until the shoulder and upper arm rests on the ball. They reported that rectus abdominis muscle activity was highest during the Swiss ball full body rolls.

Comparison between Swiss ball exercises and isolated core exercises

RECTUS ABDOMINIS

Comparing Swiss ball exercises and isolated core exercises, Escamilla et al. (2010) measured upper and lower rectus abdominis muscle activity levels. Upper rectus abdominis muscle activity was higher in the Swiss ball roll out and prone jack knife and bent-leg curl up than in the Swiss ball prone knee-tuck, Swiss ball knee-tuck with rotation, and the bent-leg sit up. Lower rectus abdominis muscle activity was higher in the Swiss ball jack knife and roll out compared to all other exercises. The Swiss ball roll out and jack knife seems to be one of the best Swiss ball exercises for the rectus abdominis.

EXTERNAL OBLIQUE

Comparing Swiss ball exercises and isolated core exercises, Escamilla et al. (2010) measured external oblique muscle activity. The Swiss ball jack knife produced the greatest external oblique muscle activity, followed by the Swiss ball prone knee-tuck with and without rotation.

Comparison between dynamic stabilisation exercises

Assessing dynamic stabilisation exercises, Souza et al. (2001) measured rectus abdominis muscle activity and external oblique muscle activity during the supine dead-bug and two point kneeling bird-dog exercise. Overall, rectus abdominis muscle activity and external oblique muscle activity levels were relatively low. Dynamic stabilisation exercises may therefore not be beneficial for developing strength in these muscles.

Summary

Unstable surface dynamic core exercises, usually performed on a Swiss ball, are commonly used for training the abdominals. However, only the Swiss ball prone jack knife can outperform curl ups for rectus abdominis and external oblique muscle activity.

Back to top of page · Back to top of section · Down to references



ISOMETRIC EXERCISES

Effect of external resistance type

Assessing the effect of external load, Vinstrup et al. (2015) measured muscle activity of the rectus abdominis and external oblique during a seated machine torso twist and a standing torso twist with an elastic band held out in front of the body and attached at 3 or 9 o’clock to the subject. They report that external oblique muscle activity was greater during the machine torso twist compared to the standing elastic condition. There was no difference in rectus abdominis muscle activity between the exercises.

Effect of moment arm length

RECTUS ABDOMINIS

Comparing plank exercises, Schoenfeld et al. (2014) assessed the plank, the long lever plank (greater shoulder flexion), the plank with posterior pelvic tilt, and the long lever plank with posterior pelvic tilt. The long lever plank variations resulted in higher rectus abdominis muscle activity compared to the standard plank variations, irrespective of posterior pelvic tilt. There was a trend towards higher rectus abdominis muscle activity in the long lever plank with posterior pelvic tilt compared to the long lever plank without posterior pelvic tilt (109% vs. 90% of MVIC). McGill et al. (2014) measured rectus abdominis muscle activity during the hanging leg raise with and without extended legs. Both rectus abdominis muscle activity and external oblique muscle activity were higher with the legs extended compared to with bent legs.

EXTERNAL OBLIQUE

Comparing plank exercises, Schoenfeld et al. (2014) assessed the plank, the long lever plank (greater shoulder flexion), the plank with posterior pelvic tilt, and the long lever plank with posterior pelvic tilt. The long lever plank variations resulted in higher external oblique muscle activity compared to the standard plank variations, irrespective of posterior pelvic tilt. There was a trend towards greater external oblique muscle activity in the long lever plank with posterior pelvic tilt compared to the long lever plank without posterior pelvic tilt (148 vs. 111% of MVC). McGill et al. (2014) measured external oblique muscle activity during the hanging leg raise with and without extended legs. Both rectus abdominis muscle activity and external oblique muscle activity were higher with the legs extended compared to with bent legs.

Comparison between abdominal hollowing and pelvic tilt

RECTUS ABDOMINIS

Comparing abdominal hollowing and pelvic tilt, Drysdale et al. (2004) assessed the differences in these actions on rectus abdominis muscle activity in the following positions: bent-leg with feet on floor, bent-leg with feet in the air (hips and knee at 90 degrees), and bent-leg with feet on a bench. Posterior pelvic tilt produced higher rectus abdominis muscle activity than abdominal hollowing in all positions.

EXTERNAL OBLIQUE

Comparing abdominal hollowing and pelvic tilt, Drysdale et al. (2004) assessed the differences in these actions on external oblique muscle activity in the following positions: bent-leg with feet on floor, bent-leg with feet in the air (hips and knee at 90 degrees), and bent-leg with feet on a bench. External oblique muscle activity was greater when performing the posterior pelvic tilt than when performing abdominal hollowing. It was also higher when performing posterior pelvic tilt in a bent-leg position with feet in the air (90 degrees at hip and knee) than in the other positions.

Comparison between isometric, isolated core exercises 

Comparing isometric, isolated core exercises, Lehman et al. (2001) found that rectus abdominis muscle activity was no different between the isometric bent leg curl-up, bent leg sit ups, supine leg raises 25cm from bench, and legs-strapped supine leg raises and shoulders-strapped curl-ups. In all conditions, rectus abdominis muscle activity was <50% of MVC. Willet et al. (2001) compared the curl up, reverse curl, curl up with twist, V-sit and abdominal hollowing. In contrast, they found that the upper and lower rectus abdominis muscle activity ranged between 10 – 85% and 20 – 90% of MVC, respectively. Upper rectus abdominis muscle activity was highest during the isometric curl up with twist. Lower rectus abdominis muscle activity was highest in the reverse curl.

Effect of surface stability

RECTUS ABDOMINIS

Assessing the effect of surface stability, Atkins et al. (2015) compared the isometric prone push up position with hands on the floor, on a Swiss ball, or in suspension straps. They found higher rectus abdominis muscle activity in the suspension strap condition compared to the floor and swiss ball conditions.

EXTERNAL OBLIQUE

Assessing the effect of surface stability, Atkins et al. (2015) compared the static prone push up position with hands on the floor, on a Swiss ball, or in suspension straps. They reported higher external oblique muscle activity in the stable floor condition compared to the other conditions.

Summary

Increasing external moment arm lengths during isometric core exercise, either by using extended legs during hanging leg raises, or by performing long lever planks, leads to greater rectus abdominis and external oblique muscle activity.  

During isometric core exercise, rectus abdominis and external oblique muscle activity are higher when using posterior pelvic tilt than when using abdominal hollowing, and when using unstable surfaces than when using stable ones

Back to top of page · Back to top of section · Down to references



REFERENCES

  1. Andersson, E. A., Nilsson, J., Ma, Z., & Thorstensson, A. (1997). Abdominal and hip flexor muscle activation during various training exercises. European journal of applied physiology and occupational physiology, 75(2), 115-123. [PubMed]
  2. Anderson, K., & Behm, D. G. (2005). Trunk muscle activity increases with unstable squat movements. Canadian Journal of Applied Physiology, 30(1), 33-45. [PubMed]
  3. Andersen, V., Fimland, M. S., Brennset, O., Haslestad, L. R., Lundteigen, M. S., Skalleberg, K., & Saeterbakken, A. H. (2014). Muscle activation and strength in squat and bulgarian squat on stable and unstable surface. International journal of sports medicine, 35(14), 1196-1202.[PubMed]
  4. Andersen, V., Fimland, M. S., Gunnarskog, A., Jungård, G. A., Slåttland, R. A., Vraalsen, Ø. F., & Saeterbakken, A. H. (2015). Core muscle activation in one-and two-armed kettlebell swing. Journal of strength and conditioning research/National Strength & Conditioning Association. [PubMed]
  5. Aspe, R. R., & Swinton, P. A. (2014). Electromyographic and kinetic comparison of the back squat and overhead squat. The Journal of Strength & Conditioning Research, 28(10), 2827-2836. [PubMed]
  6. Brown, S. H., Ward, S. R., Cook, M. S., & Lieber, R. L. (2011). Architectural analysis of human abdominal wall muscles: implications for mechanical function. Spine, 36(5), 355. [PubMed]
  7. Bressel, E., Willardson, J. M., Thompson, B., & Fontana, F. E. (2009). Effect of instruction, surface stability, and load intensity on trunk muscle activity. Journal of Electromyography and Kinesiology, 19(6), e500-e504. [PubMed]
  8. Chaffin, D. B., Redfern, M. S., Erig, M., & Goldstein, S. A. (1990). Lumbar muscle size and locations from CT scans of 96 women of age 40 to 63 years. Clinical Biomechanics, 5(1), 9-16. [PubMed]
  9. Cholewicki, J., & McGill, S. M. (1996). Mechanical stability of the in vivo lumbar spine: implications for injury and chronic low back pain. Clinical Biomechanics, 11(1), 1-15. [PubMed]
  10. Comfort, P., Pearson, S. J., & Mather, D. (2011). An electromyographical comparison of trunk muscle activity during isometric trunk and dynamic strengthening exercises. The Journal of Strength & Conditioning Research, 25(1), 149-154. [PubMed]
  11. Delp, S. L., Suryanarayanan, S., Murray, W. M., Uhlir, J., & Triolo, R. J. (2001). Architecture of the rectus abdominis, quadratus lumborum, and erector spinae. Journal of biomechanics, 34(3), 371-375. [PubMed]
  12. Drysdale, C. L., Earl, J. E., & Hertel, J. (2004). Surface electromyographic activity of the abdominal muscles during pelvic-tilt and abdominal-hollowing exercises. Journal of athletic training, 39(1), 32. [PubMed]
  13. Duncan, M. (2009). Muscle activity of the upper and lower rectus abdominis during exercises performed on and off a Swiss ball. Journal of bodywork and movement therapies, 13(4), 364-367. [PubMed]
  14. Escamilla, R. F., Francisco, A. C., Kayes, A. V., Speer, K. P., & Moorman 3rd, C. T. (2002). An electromyographic analysis of sumo and conventional style deadlifts. Medicine and science in sports and exercise, 34(4), 682-688. [PubMed]
  15. Escamilla, R. F., Lewis, C., Bell, D., Bramblet, G., Daffron, J., Lambert, S., & Andrews, J. R. (2010). Core muscle activation during Swiss ball and traditional abdominal exercises. Journal of orthopaedic & sports physical therapy, 40(5), 265-276. [PubMed]
  16. Fenwick, C. M., Brown, S. H., & McGill, S. M. (2009). Comparison of different rowing exercises: trunk muscle activation and lumbar spine motion, load, and stiffness. The Journal of Strength & Conditioning Research, 23(2), 350-358. [PubMed]
  17. Gottschall, J. S., Mills, J., & Hastings, B. (2013). Integration core exercises elicit greater muscle activation than isolation exercises. The Journal of Strength & Conditioning Research, 27(3), 590-596. [PubMed]
  18. Häggmark, T., & Thorstensson, A. (1979). Fibre types in human abdominal muscles. Acta Physiologica Scandinavica, 107(4), 319-325. [PubMed]
  19. Hamlyn, N., Behm, D. G., & Young, W. B. (2007). Trunk muscle activation during dynamic weight-training exercises and isometric instability activities. The Journal of Strength & Conditioning Research, 21(4), 1108-1112. [PubMed]
  20. Hildenbrand, K., & Noble, L. (2004). Abdominal muscle activity while performing trunk-flexion exercises using the Ab Roller, ABslide, FitBall, and conventionally performed trunk curls. Journal of athletic training, 39(1), 37. [PubMed]
  21. Imai, A., Kaneoka, K., Okubo, Y., Shiina, I., Tatsumura, M., Izumi, S., & Shiraki, H. (2010). Trunk muscle activity during lumbar stabilization exercises on both a stable and unstable surface. journal of orthopaedic & sports physical therapy, 40(6), 369-375. [PubMed]
  22. Jones, M. T., Ambegaonkar, J. P., Nindl, B. C., Smith, J. A., & Headley, S. A. (2012). Effects of unilateral and bilateral lower-body heavy resistance exercise on muscle activity and testosterone responses. The Journal of Strength & Conditioning Research, 26(4), 1094-1100. [PubMed]
  23. Karst, G. M., & Willett, G. M. (2004). Effects of specific exercise instructions on abdominal muscle activity during trunk curl exercises. Journal of Orthopaedic & Sports Physical Therapy, 34(1), 4-12. [PubMed]
  24. Konrad, P., Schmitz, K., & Denner, A. (2001). Neuromuscular evaluation of trunk-training exercises. Journal of athletic training, 36(2), 109. [PubMed]
  25. Lehman, G. J., MacMillan, B., MacIntyre, I., Chivers, M., & Fluter, M. (2006). Shoulder muscle EMG activity during push up variations on and off a Swiss ball. Dynamic Medicine, 5(1), 7. [PubMed]
  26. Lehman, G. J., & McGill, S. M. (2001). Quantification of the differences in electromyographic activity magnitude between the upper and lower portions of the rectus abdominis muscle during selected trunk exercises. Physical Therapy, 81(5), 1096-1101. [PubMed]
  27. Maddigan, M. E., Button, D. C., & Behm, D. G. (2014). Lower-Limb and Trunk Muscle Activation With Back Squats and Weighted Sled Apparatus. The Journal of Strength & Conditioning Research, 28(12), 3346-3353. [PubMed]
  28. McGill, S. M. (1991). Electromyographic activity of the abdominal and low back musculature during the generation of isometric and dynamic axial trunk torque: implications for lumbar mechanics. Journal of Orthopaedic Research, 9(1), 91-103. [PubMed]
  29. McGill, S. M., Juker, D., & Axler, C. (1996). Correcting trunk muscle geometry obtained from MRI and CT scans of supine postures for use in standing postures. Journal of biomechanics, 29(5), 643-646. [PubMed]
  30. Lander, J. E., Simonton, R. L., & Giacobbe, J. K. (1990). The effectiveness of weight-belts during the squat exercise. Medicine and science in sports and exercise, 22(1), 117-126. [PubMed]
  31. Maeo, S., Chou, T., Yamamoto, M., & Kanehisa, H. (2014). Muscular activities during sling-and ground-based push-up exercise. BMC research notes, 7(1), 192. [PubMed]
  32. Marshall, P. W., & Murphy, B. A. (2005). Core stability exercises on and off a Swiss ball. Archives of physical medicine and rehabilitation, 86(2), 242-249. [PubMed]
  33. McBride, J. M., Larkin, T. R., Dayne, A. M., Haines, T. L., & Kirby, T. J. (2010). Effect of absolute and relative loading on muscle activity during stable and unstable squatting. Int J Sports Physiol Perform, 5(2), 177-83. [PubMed]
  34. McGill, S. M., McDermott, A., & Fenwick, C. M. (2009). Comparison of different strongman events: trunk muscle activation and lumbar spine motion, load, and stiffness. The Journal of Strength & Conditioning Research, 23(4), 1148-1161. [PubMed]
  35. McGill, S. M., Juker, D., & Axler, C. (1996). Correcting trunk muscle geometry obtained from MRI and CT scans of supine postures for use in standing postures. Journal of biomechanics, 29(5), 643-646. [PubMed]
  36. McGill, S. M., Patt, N., & Norman, R. W. (1988). Measurement of the trunk musculature of active males using CT scan radiography: implications for force and moment generating capacity about the L4L5 joint. Journal of biomechanics, 21(4), 329-341. [PubMed]
  37. McGill, S., Andersen, J., & Cannon, J. (2015). Muscle activity and spine load during anterior chain whole body linkage exercises: the body saw, hanging leg raise and walkout from a push-up. Journal of sports sciences, 33(4), 419-426. [PubMed]
  38. Rankin, G., Stokes, M., & Newham, D. J. (2006). Abdominal muscle size and symmetry in normal subjects. Muscle & nerve, 34(3), 320-326. [PubMed]
  39. Reid, J. G., & Costigan, P. A. (1985). Geometry of adult rectus abdominis and erector spinae muscles*. Journal of Orthopaedic & Sports Physical Therapy, 6(5), 278-280. [PubMed]
  40. Sarti, M. A., Monfort, M., Fuster, M. A., & Villaplana, L. A. (1996). Muscle activity in upper and lower rectus abdominus during abdominal exercises. Archives of Physical Medicine and Rehabilitation, 77(12), 1293-1297. [PubMed]
  41. Saeterbakken, A. H., Andersen, V., Kolnes, M. K., & Fimland, M. S. (2014). Effects of Replacing Free Weights With Elastic Band Resistance in Squats on Trunk Muscle Activation. The Journal of Strength & Conditioning Research, 28(11), 3056-3062. [Pubmed]
  42. Saeterbakken, A. H., & Fimland, M. S. (2013). Electromyographic activity and 6RM strength in bench press on stable and unstable surfaces. The Journal of Strength & Conditioning Research, 27(4), 1101-1107. [PubMed]
  43. Santana, J. C., Vera-Garcia, F. J., & McGill, S. M. (2007). A kinetic and electromyographic comparison of the standing cable press and bench press. The Journal of Strength & Conditioning Research, 21(4), 1271-1277. [PubMed]
  44. Schoenfeld, B. J., Contreras, B., Tiryaki-Sonmez, G., Willardson, J. M., & Fontana, F. (2014). An electromyographic comparison of a modified version of the plank with a long lever and posterior tilt versus the traditional plank exercise. Sports Biomechanics, 13(3), 296-306. [PubMed]
  45. Schwanbeck, S., Chilibeck, P. D., & Binsted, G. (2009). A comparison of free weight squat to Smith machine squat using electromyography. The Journal of Strength & Conditioning Research, 23(9), 2588-2591. [PubMed]
  46. Souza, G. M., Baker, L. L., & Powers, C. M. (2001). Electromyographic activity of selected trunk muscles during dynamic spine stabilization exercises. Archives of physical medicine and rehabilitation, 82(11), 1551-1557. [PubMed]
  47. Sternlicht, E., & Rugg, S. (2003). Electromyographic analysis of abdominal muscle activity using portable abdominal exercise devices and a traditional crunch. The Journal of Strength & Conditioning Research, 17(3), 463-468. [PubMed]
  48. Teyhen, D. S., Gill, N. W., Whittaker, J. L., Henry, S. M., Hides, J. A., & Hodges, P. (2007). Rehabilitative ultrasound imaging of the abdominal muscles. journal of orthopaedic & sports physical therapy, 37(8), 450-466. [PubMed]
  49. Urquhart, D. M., Barker, P. J., Hodges, P. W., Story, I. H., & Briggs, C. A. (2005). Regional morphology of the transversus abdominis and obliquus internus and externus abdominis muscles. Clinical Biomechanics, 20(3), 233-241. [PubMed]
  50. Vera-Garcia, F. J., Grenier, S. G., & McGill, S. M. (2000). Abdominal muscle response during curl-ups on both stable and labile surfaces. Physical Therapy, 80(6), 564-569. [PubMed]
  51. Vinstrup, J., Sundstrup, E., Brandt, M., Jakobsen, M. D., Calatayud, J., & Andersen, L. L. (2015). Core Muscle Activity, Exercise Preference, and Perceived Exertion during Core Exercise with Elastic Resistance versus Machine. Scientifica, 2015. [Citation]
  52. Wahl, M. J., & Behm, D. G. (2008). Not all instability training devices enhance muscle activation in highly resistance-trained individuals. The Journal of Strength & Conditioning Research, 22(4), 1360-1370. [PubMed]
  53. Willardson, J., Fontana, F. E., & Bressel, E. (2009). Effect of surface stability on core muscle activity for dynamic resistance exercises. International journal of sports physiology and performance, 97. [PubMed]
  54. Willett, G. M., Hyde, J. E., Uhrlaub, M. B., Wendel, C. L., & Karst, G. M. (2001). Relative activity of abdominal muscles during commonly prescribed strengthening exercises. The Journal of Strength & Conditioning Research, 15(4), 480-485. [PubMed]
  55. Whiting, W. C., Rugg, S., Coleman, A., & Vincent, W. J. (1999). Muscle activity during sit-ups using abdominal exercise devices. The Journal of Strength & Conditioning Research, 13(4), 339-345. [Citation]
  56. Yavuz, H. U., Erdağ, D., Amca, A. M., & Aritan, S. (2015). Kinematic and EMG activities during front and back squat variations in maximum loads. Journal of sports sciences, 33(10), 1058-1066. [PubMed]


Top · Contents · References



CONTRIBUTORS

Adam Bentley performed the literature reviews, wrote the first draft of this page and was the primary author.

Chris Beardsley performed the first review of this page.


PROVIDE FEEDBACK

If you are knowledgable about this area of research, please help us improve this resource. Simply provide brief comments and your email address in the form below. Chris will then contact you by email to start the process of incorporating your feedback into the resource:

Your Name (required)

Your Email (required)

Your Message


Top · Contents · References