Author(s): BRUGGISSER, F., ROTH, R., RITTER, S., INFANGER, D., LEDERGERBER, R., HANSSEN, H., KNAIER, R., Institution: UNIVERSITY BASEL, Country: SWITZERLAND, Abstract-ID: 942

INTRODUCTION:
Ageing is associated with progressive declines in skeletal muscle mass and strength, increasing the risk of sarcopenia, functional impairment, and reduced quality of life. Resistance training is a key intervention to counteract these changes and is commonly prescribed using well-defined parameters such as frequency, intensity, duration, and type. However, current recommendations do not address the timing of training. Emerging evidence suggests that training responses may vary across the day due to circadian regulation of physiological functions. Given pronounced interindividual differences in the timing of peak performance, this study examined whether tailoring resistance training to an individual's peak performance time of day enhances skeletal muscle adaptations in older adults.
METHODS:
To determine individual peak and nadir times of day, participants completed standardised strength tests at four timepoints (08:00, 12:00, 16:00, and 20:00) on four separate days after a familiarisation test. Participants were then block-randomised (2:2:1) to train at their individual peak time of day, their nadir time of day, or to a non-training control group. The 12-week intervention comprised two supervised, progressive whole-body resistance training sessions (moderate-to-high loads, 8-15 repetitions) and one moderate-intensity endurance cycling session per week. Primary outcomes were isometric mid-thigh pull strength, handgrip strength and skeletal muscle mass assessed by dual-energy X-ray absorptiometry. Between-group differences at follow-up were analysed using baseline-adjusted analyses of covariance, with additional adjustment for age and sex. Effect sizes were standardised to baseline standard deviations.
RESULTS:
Of the 108 randomised participants, 93 (41% female; mean [standard deviation] age 67 [5] years; BMI 24.3 [2.7] kg/m²) were included in the analyses. Training adherence exceeded 91% for resistance and 93% for endurance sessions in both exercise groups. Absolute training loads increased progressively across all resistance exercises, with large relative increases (approximately two- to threefold) from the first to final training session. These increases were comparable between the peak and nadir groups. Across all outcomes, comparisons between peak, nadir, and control groups showed trivial effect sizes (<0.20), with no meaningful differences between training at peak versus nadir times of day.
CONCLUSION:
There is little evidence that tailoring resistance training to an individual's peak time of day provides additional benefits in terms of skeletal muscle adaptations in older adults. Similar adherence, load progression and training adaptations in the peak and nadir groups indicate that the effectiveness of resistance training is largely independent of the time of day at which it is performed. These findings suggest that older adults may prioritise flexibility in exercise timing to support adherence without compromising muscular adaptations.