The trial, published in the Journal of Cachexia, Sarcopenia and Muscle, was designed to test a hypothesis grounded in solid physiology. Human performance does not hold steady across the day. Strength and endurance typically peak in the afternoon and evening, and the underlying biology is real: skeletal muscle carries its own molecular clock, built around the CLOCK/BMAL1 transcription factors, which governs substrate use, mitochondrial function, metabolic gene expression, mTOR-mediated anabolic signalling and the secretion of myokines. Laboratory studies have shown that the same exercise session can trigger different molecular and metabolic responses depending on when it is performed, and even the anabolic signalling that follows a contraction appears to be time-of-day dependent. If the muscle’s internal clock shapes how it responds to training, then aligning workouts with the body’s daily high point seemed a plausible way to amplify adaptation.

What set the Basel study apart from earlier attempts was its individualized design. Most previous trials simply randomized volunteers to two fixed training times, most commonly 7:30 and 17:30, and compared the outcomes. That approach ignores a crucial fact: while average performance is higher later in the day, the timing of an individual’s personal peak varies enormously from person to person. In the new trial, every participant completed standardized strength tests at four times of day, 08:00, 12:00, 16:00 and 20:00, on four separate days with at least 24 hours between sessions. Researchers then randomized 108 participants in a 2:2:1 ratio to train at their personal peak time, at their personal trough time, or to maintain their habitual lifestyle as a control group. To the authors’ knowledge, this is the first randomized controlled trial to test such a peak-versus-trough design in resistance training.

The intervention itself was demanding and carefully supervised. Participants in the two training groups completed three supervised sessions per week for twelve weeks: two resistance sessions and one 30-minute endurance session on a cycle ergometer at 60 percent of their individual peak oxygen uptake. Each resistance session comprised three sets of five exercises, including leg press, chest press, deadlift, one-arm cable row and back squat, lasting 45 to 65 minutes. After a two-week familiarization period, participants trained to volitional failure, meaning they repeated each lift until they could not complete another repetition with proper technique. Loads were adjusted using a repetition-based progression algorithm, and training volume was tracked exercise by exercise. Adherence was impressively high in both groups, at roughly 91 to 93 percent for resistance sessions, and volume and load progressed in essentially identical patterns whether people trained at their peak or their trough.

The primary outcome was maximal isometric strength measured with the isometric midthigh pull, a safe and highly reproducible whole-body force test well suited to older adults. Secondary outcomes included handgrip strength and appendicular lean mass index, the gold-standard measure of limb muscle mass obtained by dual-energy X-ray absorptiometry. Crucially, the researchers assessed strength as a daily mean, averaging each participant’s maximum values across all four measurement times, so the results would not be biased by whether someone was simply tested at the hour they happened to train. Assessors were blinded to group allocation, participants and trainers were blinded to the trial hypotheses, and the analysis followed a modified intention-to-treat principle.

The baseline profiling confirmed the expected diurnal rhythm. Peak strength values occurred most often in the afternoon and evening, while troughs clustered around noon and in the morning. On average, participants were about 11 percent stronger at their peak time than at their trough, a difference of 2.6 newtons per kilogram in relative midthigh pull strength. But the individual spread was striking: some people’s daily amplitude was as little as 1 percent, while others swung by 34 percent. That variability is precisely why the investigators argued that fixed-time trials may have missed real effects, since two people assigned to the same clock time could be training at profoundly different relative physiological states.

Yet when the twelve weeks were over, the hypothesis collapsed. Everyone got stronger and leaner, including the control group to a lesser degree, but the differences between the peak and trough groups were trivial. Adjusted effect sizes hovered near zero for all three outcomes, with confidence intervals that largely overlapped zero: roughly 0.07 newtons per kilogram for midthigh pull strength, minus 0.20 kilograms per square metre for handgrip strength, and 0.04 kilograms per square metre for appendicular lean mass index. Comparisons among the fixed training times, morning, noon, afternoon and evening, told the same story, with wide, zero-overlapping confidence intervals and no consistent pattern. Even exploratory analyses of whether testing at the same time of day as training, a so-called congruent condition, conferred an advantage found nothing.

Why did aligning training with peak performance fail to pay off? The authors offer a compelling biological explanation rooted in the decentralized nature of human chronobiology. Although the suprachiasmatic nucleus in the brain acts as the master pacemaker, peripheral tissues such as skeletal muscle harbour semi-autonomous molecular clocks that do not necessarily run in synchrony with central rhythms or with each other. The systems driving acute performance, such as neuromuscular activation and thermoregulation, may peak at different hours than the cellular machinery governing muscle protein synthesis and tissue repair. Training when you are strongest, in other words, may not coincide with the window in which your muscle fibers are most responsive to growth signals. Moreover, because participants trained to volitional failure, the relative stimulus delivered to the muscle was probably comparable regardless of clock time, erasing any advantage that higher achievable loads at peak hours might have conferred.

The authors also acknowledge methodological caveats. Peak and trough times were estimated from a single four-day profiling period, so day-to-day variability in strength may have blurred the intended physiological contrast. Repeated training at a consistent hour may itself induce temporal acclimatization, flattening circadian differences over time. The cohort was relatively healthy and high-functioning, with grip strength above population averages, and early strength gains in older adults are predominantly neural rather than hypertrophic, leaving only about ten weeks of progressive overload after familiarization, which may have limited sensitivity to detect small differences in muscle mass. As a single-centre trial of healthy, independently living older adults, the findings may not extend to frail or sarcopenic populations.

The practical takeaway, however, is refreshingly liberating. For healthy older adults, resistance training appears to be equally effective whether performed in the morning, at noon, in the afternoon or in the evening, and there is no clinically meaningful benefit to scheduling workouts around a personal performance peak. Given that exercise guidelines for older adults already emphasize frequency, intensity, time and type without reference to circadian timing, this trial suggests that flexibility is the wisest policy: the best time to train is the time you can stick with. In an ageing world where more than a quarter of Europeans and North Americans will be over 65 by 2050, removing a perceived barrier to when exercise counts may do far more for muscle health than any chronobiological fine-tuning ever could.

Subject of Research: Time-of-day effects of rhythm-aligned resistance training on skeletal muscle adaptation in older adults

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

Article References: Bruggisser, F., Ritter, S., Roth, R., Ritter, E. T., Infanger, D., Ledergerber, R., Hinrichs, T., Scheer, F. A. J. L., Handschin, C., Hanssen, H., & Knaier, R. (2026). Effects of Daily Rhythm‐Aligned Training on Skeletal Muscle Adaptation in Older Adults: A Randomized Controlled Trial. Journal of Cachexia, Sarcopenia and Muscle, 17(5), Article e70390. https://doi.org/10.1002/jcsm.70390

Image Credits: AI Generated

DOI: 10.1002/jcsm.70390

Keywords: circadian rhythms, resistance training, sarcopenia, skeletal muscle, older adults, randomized controlled trial, exercise timing, muscle strength, lean mass, chronobiology, healthy ageing, molecular clock