Heavy versus light loads for muscle growth and strength
Across 28 studies that included only training in which sets were performed to volitional failure, low, moderate and high loads produced no detectable difference in muscle hypertrophy, while strength gains were greater with high-load and moderate-load training than with low-load training.
Lopez P (2021) · Medicine and Science in Sports and Exercise · PMID 33433148
It does not say load does not matter. Strength clearly favoured heavier loads (SMD 0.60-0.63 for high vs low). It also does not say you can grow equally well with light weights taken to a comfortable stopping point — the entire analysis included ONLY studies where sets were carried to volitional failure, so the null on hypertrophy is conditional on that. Nothing here licenses "high reps build as much muscle" as a general statement, and nothing here establishes the result in trained athletes specifically, since the sample is healthy adults, with greater hypertrophy effects observed in untrained participants (P = 0.033). The abstract states no training-duration range, so no claim about how long this holds is supported. The abstract reports no confidence intervals or equivalence bounds for the hypertrophy comparisons, so this is a failure to detect a difference, not a demonstration that the loads are equivalent.
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- Twenty-eightstudies
number of studies pooled in the network meta-analysis
Twenty-eight studies involving 747 healthy adults were included.
- 747healthy adults
total participants across the pooled studies
Twenty-eight studies involving 747 healthy adults were included.
- >15 repetitions maximum (RM)RM
how the review defined a low (light) load
Including only studies that performed sets to volitional failure, the effects of low- (>15 repetitions maximum (RM)), moderate- (9-15 RM), and high-load (≤8 RM) RTs were examined in healthy adults.
- 9-15 RMRM
how the review defined a moderate load
Including only studies that performed sets to volitional failure, the effects of low- (>15 repetitions maximum (RM)), moderate- (9-15 RM), and high-load (≤8 RM) RTs were examined in healthy adults.
- ≤8 RMRM
how the review defined a high (heavy) load
Including only studies that performed sets to volitional failure, the effects of low- (>15 repetitions maximum (RM)), moderate- (9-15 RM), and high-load (≤8 RM) RTs were examined in healthy adults.
- P = 0.113-0.469p-value range
overall analysis found no difference in hypertrophy between loads
Although no differences in muscle hypertrophy between RT loads were found in overall (P = 0.113-0.469) or subgroup analysis (P = 0.871-0.995), greater effects were observed in untrained participants (P = 0.033) and participants with some training background who undertook more RT sessions (P = 0.031-0.045).
- P = 0.871-0.995p-value range
subgroup analysis restricted to studies deemed of high quality also found no hypertrophy difference between loads
Although no differences in muscle hypertrophy between RT loads were found in overall (P = 0.113-0.469) or subgroup analysis (P = 0.871-0.995), greater effects were observed in untrained participants (P = 0.033) and participants with some training background who undertook more RT sessions (P = 0.031-0.045).
- P = 0.033p-value
meta-regression covariate: greater hypertrophy effects observed in untrained participants (an association across studies, not a between-load comparison)
Although no differences in muscle hypertrophy between RT loads were found in overall (P = 0.113-0.469) or subgroup analysis (P = 0.871-0.995), greater effects were observed in untrained participants (P = 0.033) and participants with some training background who undertook more RT sessions (P = 0.031-0.045).
- 0.60-0.63standardized mean difference (SMD)
strength advantage of high-load over low-load training
Muscle strength improvement was superior for both high-load and moderate-load compared with low-load RT in overall and subgroup analysis (SMD, 0.60-0.63 and 0.34-0.35, respectively; P < 0.001-0.003), with a nonsignificant but superior effect for high compared with moderate load (SMD, 0.26-0.28, P = 0.068).
- 0.34-0.35standardized mean difference (SMD)
strength advantage of moderate-load over low-load training
Muscle strength improvement was superior for both high-load and moderate-load compared with low-load RT in overall and subgroup analysis (SMD, 0.60-0.63 and 0.34-0.35, respectively; P < 0.001-0.003), with a nonsignificant but superior effect for high compared with moderate load (SMD, 0.26-0.28, P = 0.068).
- 0.26-0.28standardized mean difference (SMD)
strength difference between high and moderate load — explicitly nonsignificant
Muscle strength improvement was superior for both high-load and moderate-load compared with low-load RT in overall and subgroup analysis (SMD, 0.60-0.63 and 0.34-0.35, respectively; P < 0.001-0.003), with a nonsignificant but superior effect for high compared with moderate load (SMD, 0.26-0.28, P = 0.068).
- P = 0.068p-value
the high-vs-moderate strength comparison did not reach significance
Muscle strength improvement was superior for both high-load and moderate-load compared with low-load RT in overall and subgroup analysis (SMD, 0.60-0.63 and 0.34-0.35, respectively; P < 0.001-0.003), with a nonsignificant but superior effect for high compared with moderate load (SMD, 0.26-0.28, P = 0.068).
747 healthy adults across 28 studies. The abstract specifies "healthy adults" and distinguishes untrained participants from "participants with some training background"; it does not report sex breakdown, age range, or athlete status. Not a trained-athlete population.
Lopez P, et al. (2021)Resistance Training Load Effects on Muscle Hypertrophy and Strength Gain: Systematic Review and Network Meta-analysis.
Medicine and Science in Sports and Exercise · PMID 33433148
Meta-analysis · Twenty-eight studies · 747 healthy adults
Who funded itAuthors declare no conflicts of interest.
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