Effects of Daily Rhythm-Aligned Training on Skeletal Muscle Adaptation in Older Adults: A Randomized Controlled Trial

Ageing is associated with declines in skeletal muscle mass and strength, increasing the risk of sarcopenia, functional impairment and reduced quality of life. Resistance training is an effective intervention to counteract these changes. However, the timing of training is rarely considered, even though physiological functions follow diurnal rhythms and individuals differ in the timing of peak physical performance. Therefore, this three-arm, parallel-group, randomized controlled superiority trial evaluated whether resistance training performed at an individual's peak time of day results in greater skeletal muscle adaptations than training performed at an individual's trough time of day or maintaining habitual lifestyle in older adults.

In this single-centre, double-blind trial, participants completed standardized strength assessments at four time points (08:00, 12:00, 16:00 and 20:00) across 4 days to determine individual peak and trough performance times. Participants were then computer-based block-randomized (2:2:1) to (a) train at their individual peak time of day, (b) train at their trough time of day or (c) to a nontraining control group. The 12-week intervention (comprising a 2-week familiarization phase followed by 10 weeks of progressive training) consisted of two supervised whole-body resistance training sessions per week, each consisting of five exercises, three sets and 8-15 repetitions, as well as one moderate-intensity, 30-min endurance cycling session at 60% of the individual's peak oxygen uptake. The primary outcome was isometric midthigh pull strength; secondary outcomes included handgrip strength and appendicular lean mass index assessed by dual-energy X-ray absorptiometry. Between-group differences were evaluated using baseline-adjusted analyses of covariance including age, sex, body mass and training volume. The trial was prospectively registered (ClinicalTrials.gov: NCT06063135).

Of the 108 randomized participants (41% female; mean [standard deviation] age 67 years; body mass index 24.3 [2.7] kg·m^-2), 93 were included in the analyses. Across all outcomes, effect estimates (peak vs. trough) were close to zero with confidence intervals overlapping zero (isometric midthigh pull strength: 0.06 N·kg^-1 [95% confidence interval: -0.76 to 0.88]; handgrip strength: -0.21 kg·m^-2 [-0.68 to 0.26]; appendicular lean mass index: 0.03 kg·m^-2 [-0.09 to 0.15]), indicating no clear differences across groups. No intervention-related serious adverse events were reported.

Aligning resistance training with an individual's peak performance time did not provide evidence of superiority over trough conditions for skeletal muscle adaptations in older adults. These findings suggest that prescribing resistance training according to individualized diurnal performance timing is unlikely to provide clinically meaningful benefits over a range of training times.