Training at long versus short muscle lengths
Twelve studies in young adults found that resistance training at longer versus shorter mean muscle lengths produced trivial differences in regional muscle growth at the proximal, mid-belly and distal sites, and the percentage of posterior distributions falling within regions of practical equivalence was high across all sites. The effects did show an increasing trend from proximal to distal.
Dorian Varovic (2025) · International Journal of Sports Medicine · PMID 40570881
It does NOT say lengthened partials or long-length training are useless, and it does NOT settle whole-muscle or total hypertrophy. The question here is narrower: whether mean muscle length changes WHERE along a muscle the growth is distributed. It also does not test "full ROM vs. partial ROM" as coaches use those terms. Critically, the authors themselves flag that the "shorter" and "longer" conditions in the included studies differed by an average of only 21.8% mean muscle length, so this is not a test of extreme length contrasts. The abstract never states how long the training interventions ran, how many people were pooled, or whether the underlying studies were randomised or controlled — the words "random" and "control" do not appear in it at all. A reader must not turn this into "muscle length doesn't matter for hypertrophy" or "you can't shape a muscle, so ROM is irrelevant."
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- Twelvestudies
number of studies pooled in the Bayesian meta-analysis
Twelve studies conducted among young adults were included in the Bayesian meta-analysis.
- 0.05standardized mean difference
effect of longer vs shorter mean muscle length on growth at the proximal (25%) site; the abstract calls it trivial and its 95% quantile interval spans zero
Standardized mean differences (SMDs) indicated trivial hypertrophic effects estimated with relatively high precision between proximal (25% muscle length; SMD: 0.05 [95% quantile interval {QI}:-0.07, 0.16]; exponentiated log-transformed response ratio [lnRR]: 0.57% [95% QI:-1.92%, 3.24%]), mid-belly (50% muscle length; SMD: 0.07 [95% QI:-0.02, 0.15]; exponentiated lnRR: 1.22% [95% QI:-0.77%, 3.22%]), and distal (75% muscle length; SMD: 0.09 [95% QI:-0.01, 0.19]; exponentiated lnRR: 1.88% [95% QI:-0.44%, 4.34%]) sites.
- 0.07standardized mean difference
effect at the mid-belly (50%) site; trivial, 95% quantile interval spans zero
Standardized mean differences (SMDs) indicated trivial hypertrophic effects estimated with relatively high precision between proximal (25% muscle length; SMD: 0.05 [95% quantile interval {QI}:-0.07, 0.16]; exponentiated log-transformed response ratio [lnRR]: 0.57% [95% QI:-1.92%, 3.24%]), mid-belly (50% muscle length; SMD: 0.07 [95% QI:-0.02, 0.15]; exponentiated lnRR: 1.22% [95% QI:-0.77%, 3.22%]), and distal (75% muscle length; SMD: 0.09 [95% QI:-0.01, 0.19]; exponentiated lnRR: 1.88% [95% QI:-0.44%, 4.34%]) sites.
- 0.09standardized mean difference
effect at the distal (75%) site; the largest of the three and still described by the abstract as trivial, 95% quantile interval spans zero
Standardized mean differences (SMDs) indicated trivial hypertrophic effects estimated with relatively high precision between proximal (25% muscle length; SMD: 0.05 [95% quantile interval {QI}:-0.07, 0.16]; exponentiated log-transformed response ratio [lnRR]: 0.57% [95% QI:-1.92%, 3.24%]), mid-belly (50% muscle length; SMD: 0.07 [95% QI:-0.02, 0.15]; exponentiated lnRR: 1.22% [95% QI:-0.77%, 3.22%]), and distal (75% muscle length; SMD: 0.09 [95% QI:-0.01, 0.19]; exponentiated lnRR: 1.88% [95% QI:-0.44%, 4.34%]) sites.
- 0.57%percent (exponentiated log-transformed response ratio)
percent difference in growth at the proximal site favouring longer mean muscle lengths
Standardized mean differences (SMDs) indicated trivial hypertrophic effects estimated with relatively high precision between proximal (25% muscle length; SMD: 0.05 [95% quantile interval {QI}:-0.07, 0.16]; exponentiated log-transformed response ratio [lnRR]: 0.57% [95% QI:-1.92%, 3.24%]), mid-belly (50% muscle length; SMD: 0.07 [95% QI:-0.02, 0.15]; exponentiated lnRR: 1.22% [95% QI:-0.77%, 3.22%]), and distal (75% muscle length; SMD: 0.09 [95% QI:-0.01, 0.19]; exponentiated lnRR: 1.88% [95% QI:-0.44%, 4.34%]) sites.
- 1.22%percent (exponentiated log-transformed response ratio)
percent difference in growth at the mid-belly site favouring longer mean muscle lengths
Standardized mean differences (SMDs) indicated trivial hypertrophic effects estimated with relatively high precision between proximal (25% muscle length; SMD: 0.05 [95% quantile interval {QI}:-0.07, 0.16]; exponentiated log-transformed response ratio [lnRR]: 0.57% [95% QI:-1.92%, 3.24%]), mid-belly (50% muscle length; SMD: 0.07 [95% QI:-0.02, 0.15]; exponentiated lnRR: 1.22% [95% QI:-0.77%, 3.22%]), and distal (75% muscle length; SMD: 0.09 [95% QI:-0.01, 0.19]; exponentiated lnRR: 1.88% [95% QI:-0.44%, 4.34%]) sites.
- 1.88%percent (exponentiated log-transformed response ratio)
percent difference in growth at the distal site favouring longer mean muscle lengths; the largest of the three and still within the abstract's own description of trivial effects
Standardized mean differences (SMDs) indicated trivial hypertrophic effects estimated with relatively high precision between proximal (25% muscle length; SMD: 0.05 [95% quantile interval {QI}:-0.07, 0.16]; exponentiated log-transformed response ratio [lnRR]: 0.57% [95% QI:-1.92%, 3.24%]), mid-belly (50% muscle length; SMD: 0.07 [95% QI:-0.02, 0.15]; exponentiated lnRR: 1.22% [95% QI:-0.77%, 3.22%]), and distal (75% muscle length; SMD: 0.09 [95% QI:-0.01, 0.19]; exponentiated lnRR: 1.88% [95% QI:-0.44%, 4.34%]) sites.
- 21.8%percent mean muscle length
the average gap between the "shorter" and "longer" conditions across the included studies — the authors' own stated reason for caution
Relatively small differences between "shorter" and "longer" mean muscle length (an average difference of 21.8% mean muscle length) between conditions/groups in the examined studies warrant caution when interpreting the findings.
Young adults. That is the only descriptor the abstract provides. I ran explicit absence checks over the verbatim abstract: it contains no occurrence of "participants", "trained", "untrained", "male" or "female", and states no pooled sample size. Do not describe these people as trained lifters, and do not assert sex or an age range.
Dorian Varovic, et al. (2025)Does Muscle Length Influence Regional Hypertrophy? A Systematic Review and Meta-Analysis.
International Journal of Sports Medicine · PMID 40570881
Meta-analysis · Twelve studies
Who funded itSee the paper's funding and conflict-of-interest statement.
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