Paper
Eccentric Overload Training: A Viable Strategy to Enhance Muscle Hypertrophy?
Published Nov 1, 2017 · B. Schoenfeld, J. Grgic
Strength and Conditioning Journal
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Abstract
It has been postulated that eccentric actions have the greatest effect on muscle hypertrophy. The potential hypertrophic benefits to eccentric traini ng raise the possibility that muscular growth could be enhanced by supplementing resistance train ing with eccentric overload training. Herein we examine whether this strategy is efficacious for enhancing muscle growth. Introduction Resistance training (RT) can be carried out with 3 distinct types of muscle actions: concentric, eccentric, and isometric. Concentric ac tions occur when a muscle produces force as it shortens; eccentric actions occur when a muscle pro duces force as it forcibly elongates; and isometric actions occur when a muscle produces forc e without a change in its length (24). Of these actions, it has been postulated that eccentri actions are the most important from a hypertrophy standpoint. This hypothesis is supporte d by findings that eccentric actions elicit more rapid elevations in muscle protein synthesis a nd greater increases in intracellular anabolic signaling and gene expression versus concentric act ions (6, 11, 19, 29). However, acute studies cannot necessarily be generalizable to long-term ad apt tions. Results from longitudinal studies examining muscle actions and hypertrophy adaptation s are somewhat equivocal on the matter. While some studies show that eccentric actions prom ote greater muscle growth compared to concentric and isometric contractions (8, 13, 17, 2 0) others have failed to show significant hypertrophic differences between conditions (9, 11, 18). A recent meta-analysis by Schoenfeld et al. (28) so ught to provide clarity on this topic. Pooled analysis of 15 studies directly comparing hy pertrophic changes between different AC CE PT ED Copyright 2017 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. dynamic muscles actions showed a greater magnitude of effect for eccentric versus concentric RT, but results did not reach statistical significa n e. When quantified on a percentage basis, the average gain from eccentric actions corresponded to 10.0% compared to 6.8% for concentric actions, a finding that can be deemed potentially m eaningful from a practical standpoint. A potential confounding issue with these findings is that a majority of studies matched the number of repetitions as opposed to total work. Given that strength capacity for eccentric actions exceeds that of concentric actions by as much as 50% (1), i t cannot be ruled out that growth-related advantages favoring eccentric exercise resulted fro m the greater loads employed during training. Moreover, many of the studies were carried out usin g isokinetic dynamometry, and thus the results cannot necessarily be generalized to isoine rtial training RT commonly performed in gym settings. It has been proposed that an increase in muscle dam age ay at least partially account for the superior hypertrophic effects of eccentric acti ons (26). Although myodamage is seen with the performance of concentric and isometric training (4 , 15), eccentric exercise causes the greatest damage to muscle tissue (7), purportedly due to hei ght ned forces distributed among fewer active fibers (24). Muscle damage is considered to be ne of the three primary mechanisms of exercise-induced muscle hypertrophy (25). Although the factors responsible for this phenomenon remain to be elucidated, current theory postulates that structural microtears to contractile elements and the extracellular matrix initiates ana bolic processes to reinforce these tissues and thereby safeguard them from future injury (2). Intr iguingly, there is some evidence that concentric and eccentric actions elicit regional-sp ecific adaptive hypertrophic responses in the vastus lateralis, with greater distal growth from e ccentric actions and greater growth in the midportion of the muscle from concentric actions (11). The reasons for these findings have yet to be AC CE PT ED Copyright 2017 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. elucidated, but it has been speculated that they ma y result from regional muscle damage along the length of the fiber that in turn causes non-uni form alterations in muscle activation (16). The potential hypertrophic benefits to eccentric tr aining raise the possibility that muscular growth could be enhanced by supplementing RT with eccentric overload training (23). Such a strategy involves performing isolated eccent ric actions with a load greater than the concentric 1 repetition maximum (RM), or, performin g concentric actions at a given load, and increasing the load over the concentric 1RM on the eccentric part of the lift. Hypothetically, the greater magnitude of load used in this type of trai ning may enhance the growth response by heightening stimulation of type II fibers and incre asing structural perturbations to the working musculature. In addition, there may be beneficial e ffects on regional hypertrophic adaptations, particularly in the quadriceps femoris. Some studie s also report that eccentric overload training might increase metabolite accumulation, specificall y, b ood lactate (32). Metabolite accumulation has also been hypothesized to be an im portant factor contributing to muscle hypertrophy (27). Recently, Fisher and colleagues directly investigat ed the effects of coupling isoinertial eccentric overload training with traditional RT on measures of lean mass (10). A cohort of young, resistance-trained men and women were random ly assigned to one of three different groups: (i) a traditional training group that perfo rmed 8-12RM of combined concentric and eccentric actions twice per week; (ii) an eccentric training group that performed 1 traditional training session and 1 eccentric-only session per w eek, or (iii) an eccentric-only group that performed 2 weekly eccentric training sessions. Ecc entric training was carried out at a load equating to 105% of the subject’s 1RM, allowing mus cular failure to occur in ~6 repetitions. At the conclusion of the 10-week study period, no sign ificant differences in fat-free mass changes AC CE PT ED Copyright 2017 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. were found between conditions. While these findings suggest there is no advantage to eccentric overload training, it should be noted that measures of fat-free mass were obtained by air displacement plethysmography, which includes all no n-fat components of body composition and therefore is not specific to changes in muscle mass . Brandenburg and Docherty (3) compared a group train ing at a load of 75% of 1RM for 4 sets of 10 repetitions to a group that used the sam e load for the concentric part of the lift but increased the load to ~115% of the concentric 1RM f or the eccentric portion. In order to equate for volume load, the latter group performed 3 sets of 10 repetitions. The sample consisted of 18 young trained men and training was carried out usin g the preacher curl and supine elbow extension exercises. Magnetic resonance imaging (MR I) was used for the assessment of hypertrophy, which is considered to be the ‘gold st andard’ measurement tool (21). Surprisingly, following nine weeks of the training intervention, no pre to post-changes in muscle cross sectional occurred in both groups. Of importance is the fact that two participants in the eccentric overload group dropped-out of the study because of forearm pain, which might have been caused by this type of training. Walker et al. (31) compared the effects of accentua ted eccentric loading (concentric load + 40%) to traditional RT methods. The eccentric loa d was added using weight-releasers for the leg press, while for the leg extension the research ers manually had to add and remove weight plates. Results showed that both groups increased q ua riceps cross-sectional area from pre to post intervention, but no significant differences w ere noted between groups. Based on these findings it seems that added eccentr ic loading does not contribute to additional muscle hypertrophy. However, both Brande nburg and Docherty (3) and Walker et al. (31) used in vivo measures of hypertrophy (MRI and ultrasound, respe ctively) which do not AC CE PT ED Copyright 2017 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. detect changes at the muscle fiber level. Friedmann -Bette et al. (14) also reported that similar increases in muscle hypertrophy (as assessed by MRI ) occurred between the traditional RT and the eccentric overload group. However, in addition o MRI, an in vitro method of hypertrophy (muscle biopsy sampling) was also performed. Muscle biopsy data showed that only the group that trained with added eccentric load experienced a significant increase in the cross-sectional area of type IIX muscle fibers. In both groups, no significant changes were noted for type I and type IIA muscle fibers. Such findings support the n otion that eccentric overload training induces preferential type IIX muscle fiber hypertrophy. There also is evidence that eccentric actions may p romote different structural remodeling compared to concentric actions. Specifically, resea rch indicates that eccentric training increases the addition of sarcomeres in series (11, 22). This can favorably alter the length-tension relationship, resulting in a greater maximum veloci ty of shortening of muscle fibers (12). The extent to which eccentric overload training can pro mote in series hypertrophy remains to be determined, but the potential for eliciting such ad aptations provides a rationale for its inclusion in RT programs. Practical Applications Despite a sound hypothetical rationale, there is in sufficient direct research to draw causality as to whether eccentric overload training e hances muscle hypertrophy when combined with traditional RT. From a practical standpoint, i t is important to highlight that in some cases, e
Meta-AnalysisEccentric overload training may not significantly enhance muscle hypertrophy when combined with traditional resistance training, but it could promote preferential type IIX muscle fiber hypertrophy.
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