Muscle memory in humans: evidence for myonuclear permanence and long-term transcriptional regulation after strength training.
Level 3 - non-randomized controlled study
Prospective within-subject controlled interventional study
PubMed 39159314 · doi:10.1113/JP285675
What was done
Twelve untrained men and women performed 10 weeks of unilateral elbow-flexor strength training, followed by 16 weeks of detraining, and then 10 weeks of bilateral retraining (both the previously trained arm and the contralateral untrained control arm). Muscle biopsies were taken from the trained arm before and after both training cycles, and from the control arm before and after retraining. Samples were evaluated for fibre cross-sectional area (fCSA), myonuclear number, and global transcriptomics via RNA sequencing.
What was found
Initial training increased myonuclear counts by 13 ± 17% in type 1 fibres and 33 ± 23% in type 2 fibres, with a non-significant increase in mixed-fibre fCSA (30 ± 43%, P = 0.069). After 16 weeks of detraining, fCSA decreased while myonuclei persisted, maintaining 33% more type 2 fibre myonuclei in the trained arm compared to the control arm, alongside three differentially expressed genes (EGR1, MYL5, COL1A1). Following retraining, absolute type 2 fCSA was larger in the previously trained arm compared to control (P = 0.035), but the delta change in type 2 fCSA was not significantly different between muscles. Transcriptomic alterations during retraining involved 1338 differentially expressed genes in the control arm versus 822 in the previously trained arm.
Why it matters
This study provides direct human evidence that exercise-induced myonuclei persist through prolonged detraining. However, the retention of myonuclei did not translate into an accelerated rate of muscle hypertrophy during retraining compared to naive muscle.
Limits
The sample size was very small (n = 12) with men and women pooled together. Functional strength numbers were not provided in the abstract, and detraining was limited to 16 weeks, leaving open whether myonuclei persist across multi-year intervals.
Cited by
- supports Human muscle research does not find evidence that an increased number of myonuclei from prior exercise training is permanently retained during detraining to facilitate muscle memory.