A 12-week randomized controlled trial in 93 adults (mean age 67) found that matching resistance training to an individual's peak versus trough performance time produced virtually no difference in muscle strength or mass. Effect sizes for isometric midthigh pull strength (0.06 N·kg⁻¹), handgrip strength (−0.21 kg), and appendicular lean mass index (0.03 kg·m⁻²) all had confidence intervals crossing zero, indicating the timing manipulation had no meaningful impact on skeletal muscle adaptation.
The chronobiology of exercise has attracted growing research interest, with some earlier, often younger-cohort studies suggesting that afternoon or evening training may confer modest performance advantages due to circadian peaks in core body temperature, hormone secretion, and neuromuscular function. This trial is notable for rigorously individualizing the timing variable — using four standardized strength assessments across each day to identify personal peak and trough windows — rather than assigning blanket morning or evening slots. That methodological care makes the null result more credible, not less. For older adults concerned about sarcopenia, the practical implication is reassuring: consistency of progressive resistance training matters far more than clock-time optimization. Limitations include the single-centre design, a 10-week active training window that may be too short to amplify subtle chronobiological effects, and a relatively lean, healthy sample (BMI 24.3) that may not generalize to frailer populations. Incremental rather than paradigm-shifting, but usefully closes a question that could otherwise distract clinicians and patients from simply training regularly.