What happens to muscle when training stops
In older adults, muscle size increased significantly over 9-24 weeks of resistance training (Cohen's d 0.99; 95% CI 0.63, 1.36). Compared with post-training values, muscle size then decreased significantly after training stopped, pooled across detraining periods of 12-52 weeks (Cohen's d -0.83; 95% CI -1.30, -0.36). In subgroup analyses, the decrease reached statistical significance for 31-52 weeks of cessation (Cohen's d -1.11; 95% CI -1.75, -0.47) but not for 12-24 weeks (Cohen's d -0.60; 95% CI -1.21, 0.01). The authors conclude that training cessation is associated with a decrease in muscle size, and that the loss "might be related to detraining duration, with greater muscle loss occurring during longer duration detraining periods." The abstract reports no formal comparison of the two cessation subgroups, so the dose-response should be read as suggested by the data rather than established by it, and the authors state that future studies are required to establish the time course.
Grgic J (2022) · International Journal of Environmental Research and Public Health · PMID 36360927
It does NOT say that 12-24 weeks off costs you nothing. That subgroup was non-significant, but the point estimate was still a moderate loss (Cohen's d -0.60) with a 95% CI of -1.21 to 0.01 — the interval touches zero, it does not sit on it. Non-significant in a small subgroup drawn from a six-study evidence base is "not demonstrated", not "no effect".
It also does not report a test of the difference between the two cessation subgroups, so the apparent dose-response rests on one subgroup reaching significance and the other not, whose confidence intervals overlap substantially; the authors state only that loss "might be related to" detraining duration. I confirmed against the abstract that no meta-regression, interaction term, or between-subgroup test is reported.
The two subgroup bands also do not tile the stated 12-52 week detraining range continuously — there is a 25-30 week gap with no subgroup, a figure derived by arithmetic from the two reported bands and not something the paper itself reports — so the two bands are not points on a demonstrated curve.
The pooled estimates are within-group pre-post change scores (baseline to post-training, and post-training to post-cessation), not comparisons against a control group. No control-group contrast is reported.
It does not speak to strength (the pooled outcome is muscle size only), does not speak to trained or younger lifters, does not measure retraining or how fast muscle comes back, and gives no week-by-week timeline — the authors explicitly state future studies are required to establish the time course.
Every figure below is shown with the sentence it was taken from, so you can check it against the paper rather than trusting us.
- 0.99Cohen's d (95% CI 0.63, 1.36)
How much muscle size increased from baseline after the resistance training block, before any layoff
Compared to the baseline data, muscle size significantly increased following the resistance training intervention (Cohen's d: 0.99; 95% confidence interval: 0.63, 1.36).
- -0.83Cohen's d (95% CI -1.30, -0.36)
The overall drop in muscle size from the end of training to the end of the layoff, pooling all cessation lengths across the 12-52 week detraining range — a significant loss, and the paper's primary pooled result
Compared to the post-resistance training data, there was a significant decrease in muscle size following training cessation (Cohen's d: -0.83; 95% confidence interval: -1.30, -0.36).
- -0.60Cohen's d (95% CI -1.21, 0.01)
The drop in muscle size after 12-24 weeks off — the confidence interval crosses zero, so this did not reach statistical significance. Not a finding of no effect.
In subgroup analyses, there was no significant decrease in muscle size following 12-24 weeks of training cessation (Cohen's d: -0.60; 95% confidence interval: -1.21, 0.01).
- -1.11Cohen's d (95% CI -1.75, -0.47)
The drop in muscle size after 31-52 weeks off — a statistically significant loss within that subgroup. The abstract reports no test comparing this subgroup with the shorter one, so do not state it as significantly larger than the 12-24 week result.
There was a significant decrease in muscle size following 31-52 weeks of training cessation (Cohen's d: -1.11; 95% confidence interval: -1.75, -0.47).
- Sixstudies (eight groups)
How many studies the meta-analysis pooled — a small evidence base, and required on the face of any card
Six studies, with eight groups, were included in the review.
- 9 to 24weeks
How long the resistance training programmes ran before the layoff began
Resistance training interventions lasted from 9 to 24 weeks.
- 12 to 52weeks
The span of layoff lengths studied across the included trials
The detraining duration was from 12 to 52 weeks.
Older adults. The abstract states no mean age, no sex breakdown, and no training status beyond describing the sample as older adults, and reports no total participant count — so none is supplied here. The paper's own summary sentence reads "In summary, resistance training increases muscle size in older adults." This is not a trained-young-lifter population and must not be ported to one.
Grgic J, et al. (2022)Use It or Lose It? A Meta-Analysis on the Effects of Resistance Training Cessation (Detraining) on Muscle Size in Older Adults
International Journal of Environmental Research and Public Health · PMID 36360927
Meta-analysis · Six studies, with eight groups, were included in the review.
Who funded itSee the paper's funding and conflict-of-interest statement.
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