Does regional hypertrophy really happen?

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Training for Strength

Regional hypertrophy, or the controversial idea that we can change the shape of a muscle through training, is a concept that still seems to cause headaches.  Can we really change the shape of a muscle by using different exercises and/or methods of resistance training or does it grow in the same way irrespective of what we do to train it?  Chris Beardsley (@SandCResearch) reviews the research.

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What is the background?

What does regional hypertrophy mean?

Muscular hypertrophy is the increase in cross-sectional area or size of a muscle. Regional hypertrophy was first reviewed by Antonio (2000), where it was defined as a change in the shape of a muscle for the purposes of bodybuilding.

More recently, the term has been used to refer to differences in hypertrophy along the length of a muscle, where proximal or distal sections may display greater or less increases in size from one another. Such differences in hypertrophy over sustained periods of time may lead to changes in the shape of a muscle. It is thought that some exercises lead to growth in certain parts of a muscle while different exercises lead to growth in other parts.

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How could regional hypertrophy occur?

Antonio (2000) proposed two main ideas by which regional hypertrophy might occur. Firstly, he suggested that the compartmentalization of muscles could mean that certain areas were activated to perform certain ranges of motion of a joint action or certain movements at a joint where multiple movements are possible (such as at the hip or shoulder). Secondly, Antonio observed that researchers have noted differences in muscle fiber type between one region of a muscle and another. This could mean that different rep ranges or muscle actions could provide different stimuli to the varying regions.

Compartmentalization – compartmentalization of muscles could mean that certain areas are activated to perform certain ranges of motion of a joint action or certain movements at a joint where multiple movements are possible (such as at the hip or shoulder). Indeed, most individual muscles are not comprised of single compartments in which all the muscle fibers run from one end to the other (the arrangement of the fibers is known as the muscle architecture). Instead, each muscle is made up of several segments, which display different features. For example, a recent study by Flack (2014) reported that on the basis of anatomy and innervation the gluteus medius has 4 compartments (anterior, anterior-middle, posterior-middle, and posterior). These compartments have different nerve branches and varying pennation angles (+33.1, +13.2, -9.9, and -29.5 degrees), which means that they best suited to slightly different tasks. Indeed, on the basis of the anatomy, Flack (2014) proposed that the horizontal arrangement of the posterior fascicles relative to the femoral neck, means that they probably act primarily to stabilize the head of the femur in the acetabulum. In contrast, the other fibers, which are arranged more vertically with respect to the femur, are better positioned to perform hip abduction.

Muscle fiber type differences – researchers have indeed also noted differences in muscle fiber type between one region of a muscle and another. Lexell (1983) found that type I fibers were predominant in the deep vastus lateralis, while type II fibers were predominant in the superficial vastus lateralis. Similarly, Sola et al. (1992) found a greater proportion of type I fibers in the deep latissimus dorsi and more type II fibers superficially. Other research has also found differences between regions from proximal-to-distal as well as between regions from deep-to-superficial. This means that where different repetition ranges are used and thereby target different muscle fiber types, this could lead to preferential growth in certain parts of a muscle. More recently, Wakahara (2013) found that differences in EMG activity in certain parts of a muscle correlated with the increases in muscular size. Miyamoto (2013) found differences in muscle tissue oxygenation saturation was between distal and middle regions of the vastus lateralis during knee extension exercise.

It should be noted that these observations are purely useful for understanding how regional hypertrophy COULD occur and are not to be taken as evidence that it DOES occur. For that, we need to look at the long-term trials, which are reviewed in the next section.

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Can regional hypertrophy happen?

The following studies differences in hypertrophy between different regions of the same muscles (not between individual muscles of the same muscle group). The table below shows where there were significant differences observed between regions of the same muscle following a resistance-training program:

Regional hypertrophy

Narici (1989) assessed the effects of 60 days of unilateral resistance-training and 40 days of detraining in 4 young male subjects who trained 4 times a week with 6 sets of 10 maximal isokinetic knee extensions at 2.09 rad/s. Before and after each phase, the researchers measured quadriceps muscle cross-sectional area at 7 fractions of femur length proximally to distally using MRI scans. The researchers found that the increase in quadriceps muscle cross-sectional area was greatest at 2/10 femur length (12.0 ± 1.5%) and least at 8/10 femur length (3.5 ± 1.2%).

Housh (1992) assessed the effects of concentric isokinetic training on the muscular cross-sectional area of the forearm extensor and flexor muscles at three levels (proximal, middle, or distal) in 13 untrained male college students over an 8-week intervention. The subjects performed 6 sets of 10 repetitions of extension and flexion, 3 times per week using an isokinetic dynamometer. The researchers found significant hypertrophy in all trained muscle groups as well as preferential hypertrophy of individual muscles at specific levels.

Roman (1993) assessed changes in the muscle volume and muscular cross-sectional area of two elbow flexors in 5 elderly males using MRI scans following 12 weeks of heavy-resistance training. The subjects performed four exercises, including isokinetic dynamometer elbow flexion, barbell curls, dumbbell curls, and hammer curls for 4 sets of 8 repetitions on the dynamometer at 60, 180, 240, and 300 degrees/s and 3 sets of 8 repetitions on the other exercises. The researchers found that muscle volume and cross-sectional area of the biceps brachii and brachialis significantly increased by 13.9% and 22.6%, respectively. The researchers found that the greatest percentage increase in combined cross-sectional area of both muscles was observed at the point of maximal girth of the muscle (around 7 – 10cm along a 25cm muscle length).

Smith and Rutherford (1995) compared the effects of unilateral concentric and eccentric contractions of the quadriceps in 10 young, healthy male and female subjects over a 20-week intervention. The eccentric group used weights which were 35% higher than the concentric group. The researchers measured muscular cross-sectional area proximally (three-quarters femur length) and distally (one-quarter femur length) using computed tomography. The researchers found significant increases in muscular cross-sectional area for both concentric and eccentric groups proximally (4.6 ± 5.1% and 4.0 ± 4.3%) but not distally (3.6 ± 18.5% and 2.6 ± 14.7%).

Kawakami (1995) assessed changes in muscle thickness using B-mode ultrasound and increases in muscular cross-sectional areas using MRI scans following unilateral resistance-training of the elbow extensors in 5 males over a 16-week intervention. The subjects performed the French Press exercise, standing, with the left hand for 5 sets of 8 repetitions at 80% of 1RM. The researchers found that muscle thickness and muscular cross-sectional area both increased after training. They found that muscular cross-sectional area increased significantly in the middle sections but not at the proximal and distal ends.

Narici (1996) assessed changes in quadriceps muscular cross-sectional areas in 7 healthy males following a 6-month resistance-training intervention using 6 sets of 8 unilateral leg extensions at 80% of 1RM. The researchers found that quadriceps muscular cross-sectional area increased by 18.8 ± 7.2%, 13.0 ± 7.2%, and 19.3 ± 6.7% in the distal, central and proximal regions, respectively.

Starkey (1996) compared the effects of different volumes of resistance-training on muscle thickness in 48 untrained subjects, training 3 times per week, for 14 weeks. The subjects performed either 1 set (low volume) or 3 sets (high volume) of variable-resistance bilateral knee extension and flexion exercise to fatigue for 8 – 12 repetitions. Before and after the intervention, the researchers measured anterior, lateral, and right thigh muscle thickness, as well as vastus medialis and vastus lateralis muscle thickness at different sites with B-mode ultrasound. They measured the muscle thickness at 3 different sites proximally to distally, measuring 20, 40 and 60% of the distance from the greater trochanter of the femur to the lateral epicondyle. The researchers detected increases in muscle thickness for the low-volume group at 60% of the vastus lateralis and at both 40% and 60% for the posterior thigh, while the high-volume group increased muscle thickness in the vastus medialis, and at both 40% and 60% for the posterior thigh.

Tracy (1999) assessed the effects of unilateral leg resistance-training in 12 healthy older men and 11 healthy older women. The subjects performed 4 sets of knee extension exercise, 3 days per week for 9 weeks. The researchers found that the men displayed greater absolute increases in quadriceps muscle volume measured by MRI (1,753 ± 44 to 1,955 ± 43cm3) than the women (1,125 ± 53 vs. 1,261 ± 65cm3) but the percentage increase was similar (12% for both). The researchers noted that there appeared to be differences in the extent of regional hypertrophy in that the greatest increases in cross-sectional area seemed to be at the mid-thigh for both males and females but they did not specifically test this.

Häkkinen (2001) assessed the effects of a 21-week resistance-training intervention in 10 elderly females on muscular cross-sectional area of the quadriceps at 3/12-to-12/15 of femur length. The researchers found that muscular cross-sectional area of the whole quadriceps muscle group increased significantly over the whole length of the femur. They also found that there were significant increases at 7/15-to-12/15 for the vastus lateralis, at 3/15-to-8/15 for the vastus medialis, at 5/15-to-9/15 for the vastus intermedius, and at 9/15 only for the rectus femoris. Thus, increases in muscular cross-sectional area at different points along the length of the femur differed between individual muscles.

Kanehisa (2002) compared the effects of two different 10-week interventions comprising isometric, unilateral elbow extension training, 3 times per week in 12 young adult males. The subjects performed the same volume of training but the relative load differed between the groups. One group performed maximal voluntary contractions (MVCs) for 6 seconds per set, 12 sets per session, while the other group performed contractions at 60% of MVC for 30 seconds per set, 4 sets per session. The researchers found that the resultant hypertrophy occurred mainly in the middle portion of the muscle, while much smaller increases in muscular size were observed at the proximal and distal ends.

Seynnes (2007) assessed changes in muscle size in the central and distal regions of the quadriceps during a 35-day high-intensity resistance-training program in 7 young, healthy volunteers who performed bilateral leg extensions 3 times per week using a flywheel ergometer. The researchers found significant increases in the central and distal regions (6.5 ± 1.1% and 7.4 ± 0.8%). However, the differences between sites were not significant.

Blazevich (2007) assessed the effects of muscle action on the muscular cross-sectional area of each of the quadriceps proximally (25% from proximal end point) and distally (75% from proximal end point) using ultrasonography after a 10-week training period and a 3-week detraining period in 21 men and women. The subjects performed slow-speed (30 degrees/s) concentric-only or eccentric-only isokinetic knee extensor training. The researchers found no significant differences in regional hypertrophy between the concentric and eccentric groups. Using pooled data, the researchers found that changes in muscular cross-sectional area of the vastus lateralis and of the rectus femoris were relatively consistent along their lengths, but there was a trend for a greater increase distally than proximally in the vastus medialis, and a significantly greater increase distally than proximally in the vastus intermedius.

Melnyk (2009) assessed the effects of a 9-week resistance-training intervention and a 31-week period of detraining on 3 different regions of the quadriceps (proximal, middle, and distal) using MRI scans in 11 young males, 11 elderly males, 10 young females, and 11 elderly females. There was a significantly greater increase in the middle region than in the proximal and distal regions (5.9 ± 4.6 vs. 4.4 ± 4.6 cm2 and 4.1 ± 3.9cm2).

Matta (2011) compared muscle thickness at 3 different sites (50, 60, and 70% of arm length) of the biceps brachii and triceps brachii following a 12-week resistance-training intervention in 49 healthy untrained males. The subjects performed the bench press, lat pull-down, triceps extension, and biceps curl exercises. The researchers observed significant difference in the increases in biceps brachii muscle thickness at the proximal (12%) and distal (5%) sites. There was no significant difference between the increases in muscle thickness at the proximal and distal sites of the triceps brachii.

Wakahara (2012) and (2013) assessed the extent to which regional hypertrophy occurring following a 12-week training intervention corresponds to regional differences in muscle activation in the training session in 12 males. The researchers measured the muscular cross-sectional areas of the triceps brachii along its length using MRI scans. The researchers found that the middle area of the triceps brachii was significantly more activated than the most proximal region. Similarly, they found that the relative change muscular cross-sectional area following the training intervention was significantly greater in the middle than the proximal region.

Bloomqvist (2013) compared the effects and deep or partial squat training in 17 male students on muscular cross-sectional area of the thigh muscles, measured at 6 sites from proximal to distal on both the front and the back of the thigh. The researchers found that the deep squat group increased front thigh muscular cross-sectional area significantly in all regions but the partial squat group only increased front thigh muscular cross-sectional area significantly in the two most proximal regions. They found that the deep squat group increased back thigh muscular cross-sectional area only at the second-most proximal site and there were no other significant increases.

Ema (2013) compared resistance training-induced changes in muscle thickness of the quadriceps (vastus lateralis, vastus medialis, vastus intermedius, rectus femoris) in different regions of each muscle in 11 recreationally active men after a 12-week resistance-training program for the knee extensors. The researchers found that increases in the muscle thickness of the vastus lateralis and rectus femoris were significantly greater in the distal than in the proximal region but increases in the muscle thickness of the vastus intermedius was significantly greater in the medial than in the lateral region.

Wells (2014) assessed changes in the vastus lateralis at two measurement points (termed VL0 and VL5) after 15-weeks of periodized resistance training in 23 National Collegiate Athletic Association (NCAA) Division 1 female soccer athletes. VL0 was 50% of the straight-line distance between the greater trochanter and lateral epicondyle of the femur. VL5 was 5cm medial to VL0. The researchers found that the increase in muscle thickness was significantly greater at VL5 than at VL0.

Matta (2014) compared changes in the rectus femoris at different sites (30% and 50% of thigh length) following either isokinetic and isoinertial 14-week resistance-training programs in 35 untrained male subjects. The researchers found that isoinertial training led to significant increases in muscular cross-sectional area at both 30% and 50% of thigh length (proximal and distal), isokinetic training led to significant increases at only 50% of thigh length (distal). Thus, the increase in muscular cross-sectional area at the proximal site was greater following isoinertial training compared to following isokinetic training (47.4% vs. 14.4%). On the other hand, the increase in muscular cross-sectional area at the distal site tended to be greater following isokinetic training compared to following isoinertial training (64.7% vs. 19.5%).

Many studies that have investigated hypertrophy at different sites within the same muscle have found that some parts grow more than others, following a period of resistance-training. This suggests that resistance-training can lead to an altered shape of a muscle, as well as a change in its size.

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What factors can influence regional hypertrophy?

A small number of researchers have compared the effects of certain training variables, including muscle action, relative load, training volume, and range-of-motion on regional hypertrophy. These studies are described above and are summarized in the following table:

Regional hypertrophy methods

Muscle action (i.e. concentric vs. eccentric) and relative load do not seem to have any effect on regional hypertrophy. However, there is some evidence that training volume, range of motion and external resistance type (i.e. isoinertial vs. isokinetic) do affect the extent to which regional hypertrophy occurs.

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What are the practical implications?

Regional hypertrophy does appear to occur in a range of upper and lower body muscles. There are some indications that muscles tend to increase in size most at their points of greatest cross-sectional area.

There is some evidence that varying training volume, range of motion and external resistance type causes growth to occur in different parts of the same muscle. Therefore, variety of these training variables is recommended over the course of a training cycle.

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Does resistance-training change muscle fiber type?

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Training for Strength

Since resistance-training using conventional loading protocols is thought to lead to greater hypertrophy of type II muscle fiber areas, it might be expected to alter muscle fiber type proportion. But does this actually occur? In this article, Chris Beardsley (@SandCResearch) reviews the literature.

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What is the background?

What are muscle fiber types?

In brief, muscle fibers can be classified in three main ways: myosin ATPase histochemical staining, MHC isoform identification, and biochemical identification of metabolic enzymes (Scott, 2001). However, the most common ways involve either ATPase or MHC isoforms. Many studies now use both of these methods. For more background, see my previous article on muscle fiber types in different muscles.

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Why assess if resistance-training alters muscle fiber type?

For strength and power athletes

Muscle fiber type is thought to be one of several factors that affect performance in sports that require explosive muscle actions. Having a higher proportion of type II muscle fibers may be beneficial to athletes competing in such sports. Resistance-training might help improve explosive performance in part by changing the proportion of muscle fiber type (although the main factors are of course increases in muscular cross-sectional area, neural drive and neuromuscular co-ordination).

For endurance athletes

In contrast, having a higher proportion of type I muscle fibers is thought to be helpful for athletes competing in endurance sports. Thus, increasing type II muscle fiber proportion might be thought to be an adverse adaptation. However, in contrast to this idea, resistance-training has generally been found to be beneficial for many endurance athletes. It is thought that such improvements in arise as a result of enhancements in work economy. Whether these increases in work economy occur as an effect of muscle fiber type changes is unclear.

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What are the selection criteria for this review?

In this review, I have selected long-term trials involving a resistance-training intervention that have measured muscle fiber type using either MHC isoforms or myofibrillar ATPase, or both. Where trials have investigated concurrent training methods, I have only incorporated the group that trained using resistance-training only.

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Does resistance-training alter fiber type in untrained subjects?

The studies in the tables below have explored how resistance-training affects muscle fiber type proportion in untrained subjects. The following table shows where studies have reported significant or non-significant increases or decreases in type I and type II muscle fiber distributions:

Type one to two

The following table shows where studies have reported significant or non-significant increases or decreases in type IIa and type IIx muscle fiber distributions:

Type IIx to type IIa

It is clear that resistance-training in untrained subjects does not lead to a shift in type I to type II muscle fiber distribution.

There is also some evidence that resistance-training causes a shift in muscle fiber distribution within the sub-types of type II muscle fibers, from type IIx muscle fiber type to type IIa muscle fiber type.

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Does resistance-training alter fiber type in trained subjects?

The studies in the table below have explored how resistance-training affects muscle fiber type proportion in resistance-trained subjects:

Trained

Resistance-training seems to have little effect on muscle fiber type in resistance-trained subjects.

 

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What could explain the lack of changes?

The lack of changes observed in resistance-trained subjects could be because any changes that are likely to occur have already happened by the point at which further training is undertaken. Alternatively, it could be that the changes are very slow in this population, or it could be that the inter-individual variation is very high, which makes detecting a significant difference very difficult (leading to type II error). Further research is clearly needed in this area.

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What do we know about these studies?

If you’re curious about the methodology used in the studies cited above (i.e. whether the researchers used histochemical analysis or immunohistochemical methods, and what type of resistance-training was performed) or if you simply just want the references, here are the details and links. They’re in alphabetical order:

Aagard (2001) investigated the changes in muscle fiber type in 11 male subjects who undertook 14 weeks of heavy, lower-body resistance-training. Muscle fiber biopsies were taken from the vastus lateralis before and after the intervention and MHC isoform distribution (type I and II) was assessed.

Adams (1993) investigated the changes in muscle fiber type following 19 weeks of heavy resistance-training. They took muscle biopsies from the vastus lateralis and analyzed them biochemically for MHC composition and histochemically for fiber types with myofibrillar ATPase.

Aniansson and Gustafsson (1981) investigated the effects of resistance-training, 3 times per week for 12 weeks in 12 elderly (69 – 74-years) but otherwise healthy males. The researchers took muscle biopsies from the vastus lateralis muscle for analysis.

Bishop (1999) explored the effects of 12 weeks of lower-body resistance-training in 21 endurance-trained, female cyclists, aged 18 – 42 years. Before and after the intervention, the researchers took a muscle biopsy from the vastus lateralis and analyzed the fiber type percentage and the activities of 2-oxoglutarate dehydrogenase and phosphofructokinase.

Brown (1990) investigated the effects of 12 weeks of both upper- and lower-body resistance-training in 14 elderly males.

Campos (2002) explored the effects of different programs of resistance-training in 32 untrained men over an 8-week intervention. The subjects were divided into four groups: a low repetition group (3 – 5RM for 4 sets), an intermediate repetition group (9 – 11RM for 3 sets), and a high repetition group (20 – 28RM) who all performed 3 exercises (leg press, squat, and knee extension). Before and after the intervention, the researchers took muscle biopsy samples and analyzed fiber-type composition by reference to both ATPase and MHC isoforms.

Carroll (1998) examined the effects of resistance-training of the leg extensor and flexor muscle groups performed 2 – 3 times per week. Before and after the intervention, the researchers measured changes in MHC isoforms in the vastus lateralis.

Charette (1991) explored the effects of a 12-week resistance-training program in 27 healthy, elderly women (age 69 ± 1 years) and took muscle biopsies before and afterwards in order to assess muscle type.

Costill (1979) investigated the effects of 7 weeks of isokinetic resistance-training in 5 males in order to determine the effects on muscle enzyme activities and muscle fiber type. Before and after the intervention, the researchers took muscle biopsies and assessed fiber type using ATPase.

Côté (1988) explored the effects of concentric isokinetic resistance-training protocols separated by a 50-day detraining period on proportion of muscle fiber type and enzyme activities.

Coyle (1981) investigated the effects of an intervention involving maximal two-legged isokinetic knee extensions performed 3 times per week for 6 weeks at either 60 degrees/s or 300 degrees/s or both 60 and 300 degrees/s in college-aged males. Muscle fiber type was assessed before and afterwards using ATPase.

De Souza (2014) compared the effects of 8 weeks of concurrent, strength-only and interval training on muscle fiber type in 37 physically active males.

Farup (2014) compared the effects of 10 weeks of either resistance-training or endurance cycling on muscle fiber type. The researchers took muscle biopsies from the vastus lateralis to quantify fiber phenotype.

Häkkinen (2001) explored the effects of a 6-month resistance-training program (2 days per week) on muscle fiber proportion of the vastus lateralis in 10 middle-aged men, 11 middle-aged women, 11 elderly men and 10 elderly women.

Häkkinen (2003) compared the effects of 21 weeks of either concurrent strength and endurance training vs. resistance-training only. The researchers assessed muscle fiber proportion in the vastus lateralis using ATPase.

Hather (1991) investigated the changes in muscle fiber type following 19 weeks of heavy resistance-training involving either concentric-only or eccentric-only muscle actions in the leg press and leg extension exercises, performed 2 days per week. The researchers took muscle biopsies from the vastus lateralis and analyzed them histochemically for fiber types with myofibrillar ATPase.

Jackson (1990) assessed muscle fiber area changes from two opposing resistance-exercise training regimes in the quadriceps muscle group in 12 college-age men. One program was focused on strength (high-resistance, low-repetition) and the other on muscular endurance (low-resistance, high-repetition). The researchers took muscle biopsies from the vastus lateralis to assess muscle fiber type proportion changes.

Karavirta (2011) assessed the interference effect of combined strength and endurance training in 96 previously untrained 40 – 67-year-old men over a 21-week training period.

Kraemer (1995) compared the effects of different types of training across four training groups that performed either high-intensity strength and endurance training, upper-body only high-intensity strength and endurance training, high-intensity endurance training, or high-intensity strength training. Muscle fiber type proportion was assessed using ATPase.

Malisoux (2006) assessed the effects of plyometric training in 8 males. They took muscle biopsies from the vastus lateralis before and after the intervention and analyzed muscle fiber type according to MHC isoforms.

McCall (1996) investigated the effects of 12 weeks of intensified resistance-training (3 sessions per week, 8 exercises per session, 3 sets per exercise, 10RM per set) in 12 male subjects with recreational resistance training experience. The researchers took muscle biopsies of the biceps brachii and analyzed them using ATPase.

Netreba (2013) explored the effects of an 8-week period of leg press resistance-training on the muscle fiber type of the vastus lateralis in 30 male subjects. There were 3 different groups, who trained using 25, 65 and 85% of 1RM.

Putman (2004) investigated the effect of strength training, endurance training, and concurrent training on muscle fibre type transitions in 40 subjects using the vastus lateralis muscle. MHC isoforms were assessed in order to determine muscle fiber type.

Pyka (1994) explored the effects of a resistance-training program in 8 male and 17 female elderly subjects over a 1-year period. The researchers took muscle biopsies at baseline and after 15 and 30 weeks. The program comprised a 12-exercise circuit (3 sets of 8 repetitions at 75% of 1RM), 3 times a week.

Roman (1993) investigated changes in the structural characteristics of the elbow flexors in 5 elderly males following 12 weeks of heavy-resistance training. The researchers took muscle biopsies of the biceps brachii muscle and assessed muscle percent fiber distribution histologically with ATPase.

Scheunke (2012) assessed the effects of different types of resistance-training program in 34 untrained women in a 6-week program. All subjects performed the leg press, squats, and knee extensions 2 – 3 days per week with either 6 – 10RM for each set or 20 – 30RM for each set. Additionally, the 6 – 10RM group was subdivided into groups that performed very slow repetitions or normal speed repetitions. The researchers collected muscle biopsies and analyzed them by reference to both ATPase and MHC isoforms.

Thorstensson (1976) assessed the effects of a lower-body resistance-training program performed 3 times a week for 8 weeks by 14 male students. The researchers took muscle biopsies from the vastus lateralis for muscle fiber analysis using ATPase.

Trappe (2000) examined the effects of 12 weeks of progressive knee extensor resistance training in 7 older men who trained 3 days per week at 80% of 1RM. Before and after the intervention, the researchers took muscle biopsy samples from the vastus lateralis and analyzed the MHC isoforms.

Wang (1993) the researchers collected muscle biopsies from the vastus lateralis muscle before and after 18 weeks of resistance-training and performed fiber typing using ATPase.

Widrick (2002) assessed the effects of a 12-week period of lower-body resistance-training in 6 young male subjects. The researchers took vastus lateralis muscle biopsies and analyzed the MHC isoforms.

Williamson (2000) took muscle biopsies from the vastus lateralis examined MHC isoforms following 12 weeks of progressive knee extensor resistance-training in 7 healthy men.

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What are the practical implications?

For trained individuals

Resistance-training does not change muscle fiber type in resistance-trained individuals, whether between type I and II or between types IIa and IIx. Training protocols should not be designed to alter muscle fiber type but should take into account the existence of the various muscle fiber types present in the muscles.

For untrained individuals

Resistance-training does not change muscle fiber type in untrained individuals between type I and II muscle fibers. Training protocols should not attempt to alter muscle fiber type between type I and II muscle fibers but should take into account the existence of the various muscle fiber types present in the muscles.

Resistance-training does change muscle fiber type in untrained individuals between type IIa and IIx muscle fibers. However, the percentage of type IIx muscle fibers is small and whether such shifts can be prevented (if they are in fact undesirable) is unclear.

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What is the Bonferroni correction?

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If you’ve read a few research studies, then you will doubtless have seen the expression “Bonferroni correction” in the statistical analysis section. But what does it mean? Why is it important? In this guest post, Tim Egerton from Sport Science Tutor explains what an important recent review paper found:

Research sometimes involves making multiple comparisons between groups. However, making multiple comparisons increases the chances of making a type I error (the risk of identifying a difference when there is not really a difference). Good statistical treatment of data can reduce this risk. A popular statistical treatment used for this purpose is the Bonferroni correction. When researchers fail to use the Bonferroni correction correctly, it increases the likelihood that their paper has reported an incorrect finding. Therefore, for interpreting research properly, we need to know when it should be used.

The study: When to use the Bonferroni Correction, by Armstrong, in Ophthalmic and Physiological Optics, 2014

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What is the background?

The Bonferroni correction is commonly used to adjust probability (p) values to correct for a familywise error rate when making multiple comparisons on the same set of subjects. However, the test is so commonly used that it has become routine. And now, the routine use of this test has been criticised as resulting in a reduction in the chance of a type I error occurring at the expense of type II error.

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What are the key concepts?

The following terms and concepts are key for an understanding of this article. Especially important are type I error and type II error. The definitions are as follows:

Type I error – This is a rejection of the null hypothesis when the null hypothesis is true. In practical terms, this means finding a difference when there isn’t one.

Type II error – This is an acceptance of the null hypothesis when the null hypothesis is false. In practical terms, this means failing to find a difference when there is actually one.

Null hypothesis – This is the hypothesis that there will be no differences between groups in a study.

Familywise error rate – This is an inflation of the error rate when making a series of comparisons on the same set of subjects.

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What did the researchers do?

The researchers assessed the extent to which statistical tests, in particular the Bonferroni correction, are used to reduce the chance of a type I error in research studies. They were also interested in whether researchers routinely provide a rationale for their test selection. They did this by reviewing current practice in the use of Bonferroni and other types of correction in three journals over a 10-year period. Two searches were made to assess:

The frequency of correction of p values by any available method (Search terms: ‘multiple testing’, ‘post-hoc’ tests). The question the researchers were interested in was: did the article correct p values to reduce the chance of a type I error using any of the available methods and provide a rationale for the method used?

The specific use of the Bonferroni adjustment (Search terms: ‘Bonferroni correction’, ‘Bonferroni adjustment’, ‘Bonferroni post-hoc test’). The question the researchers were interested in was: did the study apply Bonferroni correctly and did it provide an appropriate rationale and/or discussion of its use?

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What happened?

Frequency of correction of p values

Of the 187 studies reviewed, the reviewers found that:

142 articles included multiple statistical testing, of which 95 (67%) corrected p values and 47 (33%) did not correct p values when performing multiple comparisons.

Of the 95 articles that did correct p values, only 9 provided a clear rationale for the correction (to avoid a type I error), while 86 provided no clear rationale.

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Use of Bonferroni adjustment

Of the studies reviewed, the reviewers found that:

187 used the Bonferroni correction, of which 133 (71%) provided no discussion on the rationale or discussion of the method.

Of the 54 of the articles that provided some discussion, 36 considered its relevance in reducing a type I error, 2 discussed the possibility of a type II error, 6 discussed the relevance of the Bonferroni correction and decided not to adjust p values, and 8 gave an incorrect rationale for its use.

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What did the researchers conclude?

The researchers concluded that:

The Bonferroni correction is indeed the most popular statistical test for correcting p values in studies making multiple comparisons.

The majority of studies do not consider the relative risks of type I and type II errors in relation to the use of the Bonferroni correction.

A significant number of articles do not provide any rationale or discussion of the method of correction used for multiple comparisons or its consequences.

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What are the limitations?

The researchers provided a number of recommendations for the appropriate statistical treatment of data when multiple comparisons are involved in a study. However, these recommendations were not based upon the findings from the review.

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What are the practical implications?

The appropriate use of the Bonferroni Correction appears to depend on the relative importance of avoiding a type I error or type II error in research involving multiple comparisons.

Many researchers appear to use the Bonferroni Correction without due consideration of the appropriateness of this test.

When reading research, care should be taken to appraise the statistical treatment. Inappropriate statistical treatment may cause type I or type II error, resulting in incorrect conclusions being made.

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