Many strength and conditioning coaches have previously recommended using eccentric muscle actions for enhancing hypertrophy. But how much support is there for this claim? Fortunately, a small number of studies have directly compared the effects of eccentric-only with concentric-only training on hypertrophy. Here is a summary of what we know…
What is the background?
Although some strength and conditioning coaches have recommended using eccentric-only muscle actions for maximizing hypertrophic gains, and even though eccentric-only training is common in rehabilitation circles, few lifters actually make use of eccentric-only training for bodybuilding. However, there are a number of theoretical bases upon which eccentric-only training might lead to superior results to concentric-only or stretch-shortening cycle training, as follows:
- Eccentric muscle actions are thought to lead to greater exercise-induced muscle damage than concentric muscle actions. Exercise-induced muscle damage may be one mechanism by which hypertrophy is stimulated (see Schoenfeld, 2010). However, whether this factor is as important as has previously been reported is a matter of debate at present (see further Schoenfeld, 2012).
- Eccentric-only training involves a lower energy cost for the same amount of mechanical tension (e.g. Peñailillo, 2013). In this way, lifters are able to perform a greater volume of work while taxing their work capacity to the same degree.
- Eccentric-only training enables lifters to move a larger amount of weight than during concentric-only or stretch-shortening cycle muscle actions with the same percentage of 1RM (e.g. Flanagan, 2013, and Moir, 2013), which may lead to greater mechanical tension for the same relative load.
- Eccentric muscle actions appear to preferentially target the fast-twitch muscle fibers (e.g. Hortobagyi, 2000, and Hortobagyi, 1996), which have greater capacity for growth.
Since these large differences between eccentric and concentric muscle actions exist, researchers have often neglected to control other key variables, such as volume and relative load. Often in studies, the same absolute load is used, which means that the relative load is lower in the eccentric condition (as muscles are stronger eccentrically than concentrically).
Alternatively, where the same relative load is used, the researchers often use the same set/rep scheme, which means that the volume of work performed is higher in the eccentric condition (as muscles are stronger eccentrically than concentrically). These mismatches between the variables make it difficult to compare the effects of eccentric-only and concentric-only resistance-training programs. Therefore, it is important when comparing studies to note whether the relative loads and volumes were matched.
What is the effect of muscle action on hypertrophy?
At least 15 studies have been performed comparing the effect of eccentric and concentric muscle actions on the rate of hypertrophy in mainly untrained subjects, as shown below, although one or two studies in the list were performed in trained populations.
Vikne (2006) investigated the effects of 12 weeks of either concentric or eccentric training of the elbow flexors using a bespoke elbow flexion training machine in 17 resistance-trained males. The subjects trained 2 – 3 times per week with varying loads. The exercise sessions alternated between maximum or medium loads. The maximum load was based on a repetition maximum (4 – 8RM) while the medium training load was set to 85 – 90% of the maximum load. Over a 2-week period of training, each subject completed 3 workouts with the maximum load and 2 workouts with the medium load. Inter-set rest periods were 3 – 6 minutes. In the eccentric condition, the subjects lowered the weight over 3 – 4 seconds while the concentric condition, the subjects used maximum effort. The number of sets was increased from 3 – 5 over the intervention. Therefore, the relative loads used were similar across the two conditions but it is likely that the volumes were not matched. Before and after the intervention, the researchers measured muscular cross-sectional area using a CT scan. The researchers reported that the mean anatomical elbow-flexor cross-sectional area did not change in the concentric group (+3%) but increased significantly in the eccentric group (11%).
Higbie (1996) investigated the effects of 10 weeks of unilateral concentric or eccentric isokinetic training at 60 degrees/s on quadriceps cross-sectional area in 54 untrained female subjects, as measured by magnetic resonance imaging (MRI) scans. The subjects trained 3 days per week for 10 weeks with 3 sets of 10 reps and 3-minute inter-set rest periods. The isokinetic efforts were performed maximally and therefore it is likely that the relative load was similar but that the volume was different, although these variables were not directly measured by the researchers. Using the MRI scans, the researchers measured 7 slices of the quadriceps from 20 – 80% of femur length and they reported that the mean increases in quadriceps cross-sectional area for the eccentric and concentric groups ranged from 6.0 – 7.8% and 3.5 – 8.6%, respectively. For the sum of the all 7 slices, mean increases in quadriceps cross-sectional area increased by 6.6 and 5.0% in the eccentric and concentric groups, respectively. The increase was significantly greater in the eccentric condition than in concentric condition.
Komi and Buskirk (1972) investigated the effects of eccentric or concentric training in 31 untrained male subjects. The subjects performed 6 maximal isokinetic elbow flexion contractions with either eccentric or concentric muscle actions, 4 times per week for 7 weeks. Before and after the intervention, the researchers measured the girth of the upper right and left arms. They reported that the eccentric-only group increased right upper arm girth by a greater amount than the concentric-only group (0.57 ± 0.68cm versus 0.09 ± 0.04cm). The increase in the eccentric-only group was significant while the increase in the concentric-only group was not significant.
Seger (1998) investigated the effects of 10 weeks of either eccentric or concentric isokinetic training at 90 degrees/s on knee extensor muscular adaptations in 10 moderately-trained male physical education students. Since isokinetic efforts were used, it is likely that the relative load was similar but that the volume was different. The researchers found that the cross-sectional area of the quadriceps increased by around 3 – 4% in both groups but only reached statistical significance in the eccentric training group.
Farthing (2003) investigated the effects of isokinetic concentric and eccentric training of the elbow flexors at two different velocities (180 and 30 degrees/s) in 36 subjects (13 male and 23 female) with little experience of resistance-training. The subjects trained their elbow flexors using an isokinetic dynamometer 3 times per week for 8 weeks at a set velocity (either 180 or 30 degrees/s) for 2 – 6 sets of 8 reps with maximal effort with 1 minute of intra-set rest. The researchers measured muscular cross-sectional area before and after the intervention using ultrasound. The researchers reported that the eccentric fast training condition resulted in greater muscle thickness change (13 ± 2.5%) than the concentric slow (5.3 ± 1.5%) and concentric fast (2.6 ± 0.7%) conditions, and non-significantly greater muscle thickness change than the eccentric slow training condition (7.8 ± 1.3%).
Hortobagyi (1996) investigated whether maximal eccentric-only training would lead to greater gains in muscle size than concentric-only training. They therefore recruited 15 untrained subjects who performed 36 sessions of isokinetic concentric-only or eccentric-only unilateral knee extension resistance-training for a 12-week period. The researchers reported that type I fiber areas did not change significantly in either group but type II fiber area increased approximately 10 times more in the eccentric-only training group compared to the concentric-only training group.
Hortobagyi (2000) investigated the effects of 3 weeks of knee immobilization followed by 12 weeks of retraining with eccentric-only, concentric-only or stretch-shortening cycle muscle actions in 48 untrained males and females. The subjects performed 12 weeks of maximum effort isokinetic concentric-only or eccentric-only or stretch-shortening cycle quadriceps knee extension training of the left leg at 60 degrees/s. The subjects performed 4 – 6 sets of 8 – 12 repetitions with a 1-minute inter-set rest period. The researchers reported that immobilization reduced type I, IIa and IIx muscle fibre areas by 13, 10 and 10%, respectively. They reported that hypertrophy of type I, IIa and IIx fibers was 10, 16 and 16% after eccentric-only training but only 4, 5 and 5% after concentric-only training. They reported that increases in type IIa and IIx fibers were greater than the increases in type I fibers after eccentric training.
Ben-Sira (1995) investigated the effects of eccentric-only, concentric-only, conventional and supra-maximal eccentric-only resistance training on thigh girth in 60 untrained young female students. The subjects performed knee extension exercise 2 times per week for 8 weeks. The subjects in the conventional group performed 3 sets of 10 bilateral reps with 65% of 1RM. The supra-maximal eccentric-only group performed the eccentric phase only of 3 sets of unilateral 5 reps with 130% of 1RM. Therefore, these two groups were work-matched although it is unclear whether they were matched in terms of relative load. The concentric-only and eccentric-only groups performed only the concentric or eccentric phases of 3 sets of 10 bilateral reps with 65% of 1RM. These groups were work matched with each other but were not matched in terms of relative load. The researchers found no meaningful changes in thigh girth and changes ranged from -0.7 – +0.5% over the four training groups.
Reeves (2009) investigated the effects of bilateral eccentric-only and conventional leg press and knee extension resistance-training in 19 untrained older adults. The subjects were divided into two groups who both trained 3 times per week for 14 weeks at 80% of the muscle-action specific 5RM, performing 2 sets of 10 repetitions. Thus, the relative load was matched between the two groups. However, the training volume was not matched between the two groups, although the researchers did not discern any significant differences between groups in this respect. Before and after the intervention, the researchers measured vastus lateralis muscle thickness using ultrasonography. The researchers reported that muscle thickness increased to a similar extent in both groups (by 12 ± 13% in the concentric group and by 11 ± 10% in the eccentric group).
Nickols-Richardson (2007) investigated the effects of 5 months of either unilateral concentric or eccentric isokinetic resistance-training in young female subjects. The training intervention was performed 3 days per week and comprised 1 – 5 sets of 6 reps of isokinetic knee and elbow extension and flexion at 60 degrees/s with 1 minute of intra-set rest. Before and after the intervention, the researchers measured body composition using dual-energy X-ray absorptiometry scans. They found that the concentric group gained 0.6kg (1.5%) of lean mass, while the eccentric group gained 0.7kg (1.7%). While these increases were significant, there were no differences in the increase in lean mass between the two groups.
Blazevich (2007) investigated the effect of 10 weeks of either concentric-only or eccentric-only slow speed (30 degrees/s) isokinetic knee extensor training on muscular adaptations in 21 men and women. The subjects performed 4 – 6 sets of 6 maximal knee extension reps with a 1-minute inter-set rest period 3 times a week on an isokinetic dynamometer at 30 degree/s, using either concentric-only or eccentric-only muscle actions. The isokinetic efforts were performed maximally and therefore it is likely that the relative load was similar but that the volume was different, although these variables were not directly measured by the researchers. Before and after the intervention, the researchers measured muscle volume, anatomical cross-sectional area and physiological cross-sectional area using magnetic resonance imaging (MRI) scans as well as muscle thickness using ultrasound. The researchers found that both groups increased muscular size but they reported no differences between groups. Since the researchers did not report any values for the groups separately, it is unclear whether there was a non-significant trend for one of the groups to increase muscular size by more than the other group.
Smith (1995) investigated the effects of 20 weeks of either concentric-only or eccentric-only unilateral knee extension resistance-training in 10 young males and females on strength and hypertrophy. All subjects trained using both types of loading protocol, one for each leg. The training program involved a heavier load for the eccentric group but it was not clear whether this represented the same relative load as for the concentric group. Before and after the intervention, the researchers measured muscle cross-sectional area near the knee and hip using computed tomography (CT) scans. The researchers found significant increases in muscle cross-sectional area occurred near the hip for both the eccentric-only and concentric-only conditions but there were no significant differences between the two conditions (4.0% versus 4.6%).
Jones (1987) compared the increases in the size of the quadriceps muscle following 12 weeks of either eccentric-only or concentric-only unilateral knee extension resistance-training in 6 young males and females. The training was performed 3 times per week and comprised 4 sets with a 6RM load, representing around 80% of 1RM for each muscle action. A 1-minute inter-set rest period was provided. The researchers noted that the load used for the eccentric condition was around 145% of the load used in the concentric condition. Before and after the intervention, the researchers measured the quadriceps cross-sectional area with mid-thigh X-ray computerized tomography (CT) scans. The researchers reported that the changes quadriceps cross-sectional area were not significantly different between the eccentric-only and concentric-only training groups (3.5% versus 5.7%).
Franchi (2014) investigated the effects of 10 weeks of either concentric or eccentric resistance-training in 12 young males on vastus lateralis volume, as measured by magnetic resonance imaging (MRI) scans. The subjects performed 4 sets leg presses for 8 – 10 repetitions with 80% of either concentric or eccentric 1RM. Thus the relative load was matched between the two studies. However, the load and volume used in the eccentric-only group was 1.2-fold greater than in the concentric-only group. The researchers reported that the increases in muscular volume were similar in both groups, although there was a trend towards a greater increase in the concentric group compared to the eccentric group (8% versus 6%).
Mayhew (1995) investigated the effects of concentric and eccentric training on hypertrophy in 20 untrained male and female subjects. The subjects performed either concentric or eccentric isokinetic contractions at 30 degrees/s of the quadriceps muscles for 5 sets of 10 repetitions at 90% of maximal concentric power, 3 times per week for 4 weeks. Therefore, in this study, training volume was equated but the relative load used in each condition differed – the proportion of eccentric-1RM in the eccentric condition was lower than the proportion of concentric-1RM in the concentric condition. Before and after the intervention, the researchers measured the fiber area of the type I and type II fibers. The researchers found that with the same load, performing concentric contractions led to significantly greater type II muscle hypertrophy than training with eccentric contractions (25.7% versus 18.0%) and also displayed a trend towards greater type I hypertrophy (14.3% versus 12.3%).
Most of the studies used the same relative load but different volumes of training. In most of these cases, the eccentric-training groups used greater volumes because their relative loads were greater. However, there were also many differences between the studies, with some using isokinetic training methods and others using conventional loading protocols.
There was no clear-cut difference between eccentric-only training and concentric-only training at either the significant or non-significant levels. However, there was a strong trend for eccentric-only training to display greater hypertrophy. Out of the 15 studies, 7 found a significantly beneficial effect of eccentric-only training while 1 found a significantly beneficial effect of concentric-only training. Of the 7 studies that reported non-significant effects, the results of 4 studies displayed either no differences, or were unreported. The remaining 3 studies that reported non-significant effects displayed a beneficial trend in favour of concentric-only training.
Nevertheless, a previous review and meta-analysis concluded that eccentric-only training does in fact lead to greater hypertrophy than concentric-only training (Roig, 2009). As may well be the case with training volume, it could therefore be the case that the presence of type II errors prevents the individual studies from observing the underlying effects. However, in contrast to training volume, the studies comparing eccentric and concentric muscle actions have found conflicting results at the non-significant level.
Eccentric muscle actions may lead to greater hypertrophy than concentric muscle actions but the literature is far from being conclusive.
The following table sets out the significant and non-significant results of all of the studies:
What are the practical implications?
For strength athletes, bodybuilders and physique athletes
Eccentric-only training may lead to slightly greater hypertrophy than concentric-only training. Individuals seeking hypertrophy should make use of eccentric muscle actions in their programming to maximize increases in muscular size.