Strength training at high versus low external resistance in older adults: Effects on muscle volume, muscle strength, and force–velocity characteristics
Introduction
Human aging is characterized by a progressive decline in skeletal muscle mass, accompanied by marked decreases in muscle strength and muscular function. These losses can have a significant impact on a person's ability to independently perform activities of daily life (Abellan van Kan, 2009, Marcell, 2003). It is clear that effective interventions are needed to prevent or reverse these losses in older adults.
For optimal muscle growth, strengthening exercise at moderate to high external resistance (70–85% of the one repetition maximum (1RM)) is recommended (American College of Sports Medicine, 2006). However, practitioners remain reluctant to prescribe exercises that challenge the musculoskeletal system of older adults at high external resistances (Abellan van Kan et al., 2009). Interestingly, numerous studies suggest that low-resistance exercise, with vascular occlusion, can induce gains in muscle volume and strength equivalent to those observed after training at higher resistances (Karabulut et al., 2010, Loenneke et al., 2012, Takarada et al., 2000). In line with these and other (Taaffe et al., 1996, Tanimoto and Ishii, 2006, Van Roie et al., 2013) findings, Mitchell et al. (2012) provided evidence that lifting low resistances to the point of momentary muscle fatigue (failure) leads to hypertrophy and strength gains roughly equivalent to those achieved with conventional high-resistance training. This would suggest that the use of high external resistances may not be a necessity to elicit muscle hypertrophy.
Rather than having to be exposed to high external resistances, achieving maximal effort might be of greater importance for gains in muscle mass and strength (Carpinelli, 2008, Goto et al., 2005, Rooney et al., 1994, Schott et al., 1995). Maximal effort is typically reached when performing a series of repetitions to the point of momentary muscle fatigue. This maximal effort might be needed to maximize motor unit recruitment and thus to enhance the hypertrophic response (Carpinelli, 2008, Goto et al., 2005).
In previous research, endurance-type strength training regimens have been compared to traditional high-resistance training. Effects on muscle mass and muscle strength, however, remain inconclusive (Anderson and Kearney, 1982, Campos et al., 2002, Holm et al., 2008, Taaffe et al., 1996). Remarkably, most endurance-type protocols restricted the number of repetitions per set to about 20 or 30. Takarada and Ishii (2002) suggested that, in these protocols, the interset rest period should be kept short (~ 30 s) to reduce metabolite clearance, which in turn creates the need for additional motor unit recruitment in subsequent sets. One can expect that high-repetition exercise protocols (≥ 60 repetitions) would also be effective to maximize motor unit recruitment. However, to date, virtually no studies have focused on the effects of such high-repetition protocols.
Another interesting approach to further optimize motor unit recruitment might be to vary training resistance. Training resistance can vary not only over the course of a training period (periodization), but also from set to set within a single training session (Tan, 1999). A previous study by Goto et al. (2004) suggested that adding a single set of exercise at 50% of 1RM to a strength-type regimen at 90% of 1RM may optimize strength adaptation. A recent study tested a strength training protocol in young adults, in which a highly fatiguing protocol of 60 repetitions at 20–25% of 1RM was immediately followed (no rest) by a set of 10 repetitions at 40% of 1RM. This mixed low-resistance exercise protocol showed interesting benefits on dynamic strength and speed of movement of the knee extensors (Van Roie et al., 2013). Especially in older adults, these muscle parameters are of major importance in activities of daily living (Sayers et al., 2005, Van Roie et al., 2011).
In this study, the purpose was to compare the effects of low-resistance training at high repetitions with traditional high-resistance training at low repetitions (HIGH) on muscle volume, muscle strength, and force–velocity characteristics in older adults. To further investigate the beneficial effect of varying training resistance within a single training session, two low-resistance exercise protocols were created: one high-repetition low-resistance protocol (LOW) in which external resistance was kept constant within one session, and also one mixed high-repetition low-resistance protocol (LOW +) in which resistance was increased after 60 repetitions. All training protocols were designed to end with maximal effort (i.e. muscle fatigue and failure to continue the exercise). If performing repetitions to the point of momentary muscle fatigue is sufficient to reach (near) maximal motor unit recruitment, and thus to activate type II muscle fibers, all exercise protocols would be expected to be effective in improving muscle volume, muscle strength, and force–velocity characteristics. However, it might be possible that, in addition to muscle fatigue, a mechanical stimulus is needed to activate type II muscle fibers, especially when training at very low external resistances (protocols with many repetitions). If that is the case, increasing the resistance in LOW + at the end of a high-repetition protocol should allow this group to obtain better effects than LOW on muscle volume, muscle strength, and force–velocity characteristics.
Section snippets
Study participants
Community-dwelling adults aged 60 and older were locally recruited through advertisements and oral communications for inclusion in a 12-week resistance training program. Exclusion criteria were current participation in structured endurance exercise and/or participation in resistance exercise in the last 6 months prior to the study, knee or hip problems, unstable cardiovascular disease, neuromuscular disease, and acute hernia. A flowchart of the study is provided in Fig. 1. Fifty-six older men
Baseline characteristics and training adherence
No side effects of the intervention were reported in any of the groups. All subjects completed the study. However, two Biodex measurements (one baseline for HIGH, one post for LOW +) failed due to a lack of compliance of the participants with the test instructions and were excluded from analysis. Overall adherence (number of training sessions attended as a percentage of the total number of training sessions) to the training program was 95.7% in HIGH, 95.8% in LOW, and 95.3% in LOW +, with no
Discussion
In this study, we investigated whether high-repetition low-resistance exercise protocols (LOW and LOW +) would be similarly effective in achieving gains in muscle volume, muscle strength, force–velocity characteristics, and functional performance as traditional high-resistance training (HIGH). This question is of great importance for older adults, as muscle volume and strength decline with aging and since practitioners remain skeptical about applying high-resistance exercise in this population.
Conflict of interest
The authors have no conflicts of interests.
Acknowledgments
We would like to acknowledge the Research Foundation Flanders, Belgium (FWO-Vlaanderen), as E. Van Roie is a Ph.D. Fellow of FWO. Also, the authors are very grateful to Sports and Health Center Respiro (Rotselaar, Belgium) for the use of the training equipment.
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2022, Science and SportsCitation Excerpt :However, because all the studies except one ranged from 8–10 weeks [38], it is likely that other factors associated with the shorter and longer durations led to the trend towards significance for this moderator. One variable that stands out is repetitions performed to failure or sets using RM which were not prescribed for the two studies that had the longest duration [7,38]. This may have led towards these two studies finding no significant difference in LME assessed via %1RMPOST following lower and higher repetitions [7,38], and ultimately influenced the results for “training duration” from the meta-regression.