Older Adults Exercising On Time

There are indications from epidemiological cohort studies and animal experiments that timing of physical activity (also referred as "chronoactivity"), irrespective of intensity, impacts health and disease. In view of the detrimental effects of circadian misalignment, the large group of older people suffering from sleep problems, and the seeming importance of chronoactivity, the investigators will perform a randomised cross-over study that aims to uncover the effect of timing of physical activity on insomnia severity and related(circadian) health parameters in older adults with self-reported sleep problems. Here, the investigators hypothesize that timing of physical activity has a beneficial impact on insomnia symptoms and on circadian rhythms of additional health parameters (e.g., metabolic, psychosocial) in older people. To study this research hypothesis, the investigators will examine the effect of physical activity timing on insomnia severity in older adults with self-reported sleep problems. In addition, the investigators will examine the effect of physical activity timing on exploratory rhythmic parameters of biological clock function, physiology and metabolism, mental health, behavioural factors, and immune and cell signalling functions. For this study, a two-armed randomised cross-over study, Dutch speaking older adults between 60 and 80 years old (male and female) and having sleep problems (insomnia severity index\>10 points) from the general population in the Netherlands will be selected as participants for this study. Participants will perform one sedentary period and two period of increased physical activity with different daily patterns: 1)active morning; 2) active evening with a duration of 14 days each. In both active intervention arms, participants will follow an exercise program containing outdoor physical exercise sessions (Vitality Club) containing endurance and strength exercises, relative rest days of 30 minutes light intensity physical activity,