Hypertrophy
Meta-Analysis
2015
Dose-Response Relationships of Resistance Training in Healthy Old Adults: A Systematic Review and Meta-Analysis
By Regis Borde, Tibor Hortobagyi and Urs Granacher
Sports Medicine, 45(12), pp. 1693-1720
Abstract
<h2>Abstract</h2> <p>Sarcopenia—the progressive, age-related loss of skeletal muscle mass and function—is a pervasive condition affecting the older adult population, with substantial consequences for physical function, independence, metabolic health, and mortality risk. Resistance training is recognized as the most effective intervention to counteract sarcopenic muscle loss, yet the optimal <a href="/terms/dose-response-relationship/" class="term-link" data-slug="dose-response-relationship" title="dose-response">dose-response</a> parameters for eliciting maximal hypertrophic and strength adaptations in older adults have not been definitively established. The present <a href="/terms/systematic-review/" class="term-link" data-slug="systematic-review" title="systematic review">systematic review</a> and <a href="/terms/meta-analysis/" class="term-link" data-slug="meta-analysis" title="meta-analysis">meta-analysis</a> synthesized available evidence from randomized controlled trials examining the effects of resistance <a href="/terms/training-volume/" class="term-link" data-slug="training-volume" title="training volume">training volume</a>, intensity, frequency, and duration on measures of <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="muscle hypertrophy">muscle hypertrophy</a> and maximal strength in healthy older adults.</p> <p>A comprehensive database search identified 25 eligible randomized controlled trials enrolling 1,079 participants aged 60 years and older. Random-effects meta-analysis was conducted for muscle mass (<a href="/terms/lean-body-mass/" class="term-link" data-slug="lean-body-mass" title="lean body mass">lean body mass</a>, appendicular lean mass, or <a href="/terms/cross-sectional-area/" class="term-link" data-slug="cross-sectional-area" title="CSA">CSA</a>), maximal strength (<a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>), and functional outcomes. Moderator analyses examined training intensity (%1RM), <a href="/terms/training-frequency/" class="term-link" data-slug="training-frequency" title="weekly frequency">weekly frequency</a>, session volume (sets per exercise), and program duration as potential predictors of adaptation magnitude.</p> <p>Results demonstrated that older adults are capable of achieving significant muscle hypertrophy and strength gains through <a href="/terms/progressive-overload/" class="term-link" data-slug="progressive-overload" title="progressive resistance">progressive resistance</a> training. Optimal training parameters for hypertrophy included moderate-to-high intensities (60–80% 1RM), a frequency of 2–3 sessions per week, and program durations exceeding 12 weeks. Importantly, higher training intensity emerged as the strongest predictor of lean mass gains in this population. These findings provide evidence-based guidance for designing resistance training programs tailored to the physiological characteristics and health objectives of older adults [1].</p>Introduction
<h2>Introduction</h2> <p>The demographic transition toward older populations in developed and developing nations has elevated the health burden of sarcopenia to a major public health concern. Skeletal muscle mass peaks in early adulthood and declines at a rate of approximately 1–2% per year from the fourth decade onward, with the rate of loss accelerating after age 60–65 [1]. This involuntary reduction in muscle mass is accompanied by disproportionate losses in muscle strength and power, which together compromise physical function, increase fall risk, worsen metabolic profiles, and ultimately threaten independence and longevity. The aggregate economic costs associated with sarcopenia-related disability and hospitalization are substantial and escalating.</p> <p>While multiple interventions have been proposed to attenuate sarcopenic muscle loss—including nutritional strategies, pharmacological approaches, and various exercise modalities—resistance training remains the most robustly supported intervention for preserving and augmenting skeletal muscle mass in older adults [2]. The mechanistic rationale is clear: progressive <a href="/terms/mechanical-tension/" class="term-link" data-slug="mechanical-tension" title="mechanical loading">mechanical loading</a> stimulates <a href="/terms/muscle-protein-synthesis/" class="term-link" data-slug="muscle-protein-synthesis" title="muscle protein synthesis">muscle protein synthesis</a>, activates <a href="/terms/satellite-cells/" class="term-link" data-slug="satellite-cells" title="satellite cells">satellite cells</a>, and promotes myofibrillar remodeling, counteracting the anabolic resistance and elevated catabolic signaling that characterize aged muscle. However, aged skeletal muscle exhibits attenuated anabolic sensitivity compared with young muscle, requiring consideration of whether standard resistance training prescription recommendations derived primarily from studies on young populations are equally applicable to older adults.</p> <p>Several age-related physiological alterations may influence the hypertrophic response to resistance training in older populations. These include reduced androgen and growth hormone secretion, impaired <a href="/terms/mtor/" class="term-link" data-slug="mtor" title="mTORC1">mTORC1</a> signaling in response to mechanical and nutritional stimuli, diminished satellite cell responsiveness, increased intramuscular adipose tissue infiltration, and mitochondrial dysfunction. These changes suggest that older adults may require different training parameters—particularly with respect to intensity, frequency, and program duration—to achieve comparable relative hypertrophic responses [3].</p> <p>The optimal dosing of resistance training for older adults is therefore a question of both scientific importance and clinical urgency. Existing guidelines, including those from the American College of Sports Medicine and the World Health Organization, provide general recommendations but do not specify evidence-based optimal dose parameters for maximal hypertrophic adaptation in this population. The present <a href="/terms/systematic-review/" class="term-link" data-slug="systematic-review" title="systematic review">systematic review</a> and <a href="/terms/meta-analysis/" class="term-link" data-slug="meta-analysis" title="meta-analysis">meta-analysis</a> was conducted to address this gap by quantitatively examining <a href="/terms/dose-response-relationship/" class="term-link" data-slug="dose-response-relationship" title="dose-response">dose-response</a> relationships between resistance training variables and hypertrophic and strength outcomes in healthy older adults.</p>Methods
<h2>Methods</h2> <h3>Database Search and Study Selection</h3> <p>A systematic search of PubMed/MEDLINE, EMBASE, Cochrane CENTRAL, CINAHL, and SPORTDiscus was conducted. Search terms included "resistance training," "strength training," "<a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="muscle hypertrophy">muscle hypertrophy</a>," "<a href="/terms/lean-body-mass/" class="term-link" data-slug="lean-body-mass" title="lean body mass">lean body mass</a>," "muscle mass," "<a href="/terms/cross-sectional-area/" class="term-link" data-slug="cross-sectional-area" title="cross-sectional area">cross-sectional area</a>," "older adults," "elderly," "aging," "sarcopenia," "<a href="/terms/dose-response-relationship/" class="term-link" data-slug="dose-response-relationship" title="dose-response">dose-response</a>," "intensity," and "frequency" in various Boolean combinations. The search was restricted to randomized controlled trials published in peer-reviewed journals. Two independent investigators screened titles and abstracts, with full-text review for potentially eligible studies.</p> <h3>Inclusion Criteria</h3> <p>Studies were included <a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="if">if</a> they: (a) were RCTs with a <a href="/terms/squat-depth/" class="term-link" data-slug="squat-depth" title="parallel">parallel</a>-group design including a resistance training group and a non-exercise control group; (b) enrolled participants with a mean age ≥60 years who were classified as healthy (no conditions precluding exercise participation); (c) implemented a <a href="/terms/progressive-overload/" class="term-link" data-slug="progressive-overload" title="progressive resistance">progressive resistance</a> training intervention for ≥8 weeks; (d) reported outcomes for muscle hypertrophy (lean body mass, appendicular lean mass by DXA, or muscle CSA by CT/MRI/ultrasound) and/or maximal strength (<a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>); and (e) reported sufficient statistical data for <a href="/terms/effect-size/" class="term-link" data-slug="effect-size" title="effect size">effect size</a> computation. Studies involving clinical populations (cancer, COPD, diabetes as primary diagnosis), concurrent aerobic training without separation from resistance training effects, or very low sample sizes (n 8 per group) were excluded.</p> <h3>Training Variables Coded</h3> <p>The following training variables were extracted and coded as continuous moderators for meta-regression: (1) training intensity (<a href="/terms/relative-load/" class="term-link" data-slug="relative-load" title="% 1RM">% 1RM</a> at initial prescription or mean across program); (2) <a href="/terms/training-frequency/" class="term-link" data-slug="training-frequency" title="training frequency">training frequency</a> (sessions per week); (3) session volume (mean sets per exercise or total sets per session); (4) program duration (weeks); and (5) <a href="/terms/protein-supplementation/" class="term-link" data-slug="protein-supplementation" title="protein supplementation">protein supplementation</a> (yes/no, as covariate). Participant characteristics coded included mean age, percentage female, and baseline muscle mass proxy.</p> <h3>Statistical Approach</h3> <p>Primary analyses computed Hedges' g effect sizes comparing resistance training to non-exercise control conditions. Random-effects models were employed throughout. Subgroup analyses stratified by training intensity (low: 60% 1RM; moderate: 60–79% 1RM; high: ≥80% 1RM) and frequency (1×/wk, 2×/wk, 3×/wk). Weighted least-squares meta-regression assessed independent associations between continuous training variables and effect sizes while controlling for covariates [4].</p>Results
<h2>Results</h2> <h3>Included Studies and Participants</h3> <p>The systematic search identified 4,621 records. After deduplication and title/abstract screening, 143 full-text articles were reviewed. Twenty-five RCTs met all inclusion criteria, representing 1,079 participants (mean age 67.3 ± 5.1 years; 58% female). Program durations ranged from 8 to 52 weeks, training frequencies from 1 to 3 sessions per week, and prescribed intensities from 40% to 85% <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a> [1].</p> <h3><a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="Hypertrophy">Hypertrophy</a> Outcomes</h3> <p>Resistance training produced significant overall hypertrophy compared with non-exercise controls (Hedges' g = 0.49, 95% CI: 0.36–0.62, p 0.001; I² = 41%). This effect represents an average lean mass gain of approximately 1.1 kg or a 4.1% increase in <a href="/terms/cross-sectional-area/" class="term-link" data-slug="cross-sectional-area" title="muscle CSA">muscle CSA</a> across included studies.</p> <p><strong>Effect of training intensity</strong>: Subgroup analysis by intensity revealed a <a href="/terms/dose-response-relationship/" class="term-link" data-slug="dose-response-relationship" title="dose-response relationship">dose-response relationship</a>. Low-intensity training (60% 1RM) produced a small, non-significant effect (g = 0.21, 95% CI: −0.04 to 0.46), moderate-intensity training (60–79% 1RM) produced a moderate significant effect (g = 0.48, 95% CI: 0.31–0.65), and high-intensity training (≥80% 1RM) produced the largest effect (g = 0.67, 95% CI: 0.44–0.90). Meta-regression confirmed that training intensity was the strongest independent predictor of hypertrophy <a href="/terms/effect-size/" class="term-link" data-slug="effect-size" title="effect size">effect size</a> (β = 0.012 per <a href="/terms/relative-load/" class="term-link" data-slug="relative-load" title="% 1RM">% 1RM</a>, p = 0.003) [2].</p> <p><strong>Effect of <a href="/terms/training-frequency/" class="term-link" data-slug="training-frequency" title="training frequency">training frequency</a></strong>: Training 3 times per week produced marginally greater hypertrophy (g = 0.54) compared with 2 times per week (g = 0.47), though this difference was not statistically significant in subgroup comparisons (p = 0.38). Training once per week produced smaller effects (g = 0.29) that were significantly inferior to higher frequencies (p = 0.04).</p> <p><strong>Effect of program duration</strong>: Programs exceeding 12 weeks produced larger effects (g = 0.57) than shorter programs (g = 0.33; p = 0.02), suggesting that accumulated training stimulus over time is particularly important in this population.</p> <h3>Strength Outcomes</h3> <p>Resistance training produced substantial maximal strength gains across all included studies (g = 1.12, 95% CI: 0.89–1.35, p 0.001), confirming robust neuromuscular adaptability in older adults. Strength gains showed a similar intensity-dependent pattern, with higher-intensity training producing larger strength improvements (g = 1.41 at ≥80% 1RM vs. g = 0.73 at 60% 1RM) [3].</p>Discussion and Practical Implications
<h2>Discussion and Practical Implications</h2> <h3>Older Adults Retain Substantial Hypertrophic Capacity</h3> <p>The overarching message of this <a href="/terms/meta-analysis/" class="term-link" data-slug="meta-analysis" title="meta-analysis">meta-analysis</a> is unambiguous: older adults retain significant capacity for skeletal <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="muscle hypertrophy">muscle hypertrophy</a> in response to <a href="/terms/progressive-overload/" class="term-link" data-slug="progressive-overload" title="progressive resistance">progressive resistance</a> training, with effect sizes approaching those reported in comparable meta-analyses of younger populations. This finding challenges persistent clinical nihilism regarding resistance training for the elderly and provides strong empirical support for aggressive inclusion of resistance training in health promotion and sarcopenia prevention programs targeting older adults [1].</p> <p>The mean hypertrophic effect (Hedges' g = 0.49) observed here represents a clinically meaningful gain in lean mass that has functional implications. Incremental gains in muscle mass are associated with improvements in gait speed, stair-climbing ability, chair-rise time, and balance—all key determinants of independence and fall prevention in older adults. The <a href="/terms/squat-depth/" class="term-link" data-slug="squat-depth" title="parallel">parallel</a> observation of large strength gains (g = 1.12) further underscores the functional utility of resistance training in this population.</p> <h3>Training Intensity as the Primary Driver</h3> <p>The demonstration that training intensity is the strongest predictor of hypertrophic adaptation in older adults has direct implications for program design. The frequently observed clinical tendency to prescribe only light resistance training (Thera-bands, very low-weight machines) to older adults—motivated by concerns about injury and effort intolerance—appears misaligned with the evidence. While low-intensity training does produce some benefit, and may be appropriate as a starting point for very deconditioned or frail individuals, the <a href="/terms/dose-response-relationship/" class="term-link" data-slug="dose-response-relationship" title="dose-response">dose-response</a> analysis clearly indicates that progressive escalation toward moderate-to-high intensities (60–80% <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>) is necessary to maximize muscle hypertrophy [2].</p> <p>Practically, this means that resistance training programs for older adults should incorporate compound, multi-joint exercises (squats, deadlifts, leg presses, rows, presses) at loads that generate meaningful muscle fatigue within the 8–15 repetition range, and that loads should be progressively increased as strength improves. Safety concerns are legitimate but should not serve as a rationale for permanently avoiding moderate-to-high loads; rather, appropriate supervision, technique instruction, and graduated load progression effectively manage injury risk in most older adult populations [3].</p> <h3>Frequency, Duration, and Programming Considerations</h3> <p>The evidence supports training each major muscle group 2–3 times per week, with programs of at least 12 weeks duration required to observe substantial hypertrophic adaptation. The relatively attenuated acute anabolic response to exercise in older muscle (due to anabolic resistance) may necessitate more repeated stimulation to achieve the same cumulative anabolic effect as younger individuals. Protein intake optimization—targeting 1.6–2.2 g/kg/day with <a href="/terms/leucine/" class="term-link" data-slug="leucine" title="leucine">leucine</a>-rich protein sources—should be considered an integral component of a resistance training program for older adults, as the synergy between mechanical stimulus and nutritional support is particularly important in anabolic-resistant aged muscle.</p> <p>Exercise selection should prioritize functional movement patterns (pushing, pulling, squatting, hinging) that translate directly to activities of daily living. Power training (performing concentric phases rapidly with submaximal loads) may be incorporated alongside traditional hypertrophy-focused training to optimally address the age-related decline in rapid force production capacity, which falls disproportionately faster than maximal strength with aging [4].</p>관련 논문
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