Influence of training time in a 12-week training intervention on cardiorespiratory fitness

Cardiorespiratory fitness is a key factor in healthspan, especially for older adults. Evidence shows that endurance and strength performance vary within individuals throughout the day, yet it remains unclear if training at peak offers advantages for enhancing performance or health outcomes. This master thesis aimed to investigate the effects of training time (nadir vs. peak) on ̇VO2peak improvements in adults aged 60-80 years over a 12-week intervention.
Thirty-two participants were randomized to train at either their individual nadir or peak, deter-mined by pre-intervention strength testing across four times of day (08:00, 12:00, 16:00, 20:00). Participants completed supervised strength training twice weekly and endurance train-ing once weekly on an ergometer with target heart rate at 60% of individual ̇VO2peak. Changes in ̇VO2peak (L/min) from pre- to post-intervention were analyzed, with ANCOVA adjusting for baseline fitness.
The mean difference in ̇VO2peak was 0.14 (0.24) L/min (95% CI: 0.01, 0.27) in the nadir group (p = 0.041) and 0.21 (0.37) L/min (95% CI: -0.07, 0.49) in the peak group (p = 0.119). Post-intervention, direct comparison between groups showed a mean difference of 0.01 (0.27) L/min (95% CI: -0.56, 0.54), slightly favoring the nadir group (p = 0.514).
The results show that both the nadir and peak training groups improved ̇VO2peak, with no significant differences between them. This suggests that regular physical activity has a positive effect on ̇VO2peak in older adults, regardless of the time of day of training, emphasizing the importance of consistency of training rather than specific timing.