The circadian clock: an important factor modifying the effect of physical activity on the lifespan of Drosophila melanogaster.

It is well established that the circadian clock has pronounced effects on functioning of cells, tissues and body organs. Little, however, is known regarding its role in the body's adaptation to physical activity. The aim of the present study was to establish the effect of physical activity-performed at either the activity peak (ZT1) in the morning or during 'siesta' time (ZT6) in the middle of the day-on the lifespan of male and female Drosophila melanogaster. Three‑day‑old virgin flies (separated by sex) were allocated to control or exercise groups. Flies in the exercise groups were subjected to exercise every day by applying motor stimulation at ZT1 or at ZT6. Overall lifetime physical activity of controls was lower in male D. melanogaster compared to females. Forced physical activity at ZT1 prolonged the male lifespan by ~35%, whereas females in the same group exhibited a lifespan reduction of ~84%. In contrast, physical activity performed at 'siesta' time shortened the lifespan of both male and female flies, by ~20% and ~67%, respectively. Forced locomotor activity performed during the time of peak natural daily activity prolonged life expectancy in males but had a negative effect on female longevity. Interestingly, when physical activity was applied during the 'siesta' time, it shortened the lifespan regardless of sex. Therefore, our study suggests that synchronizing physical activity to the daily rhythm of activity and rest dictated by the circadian clock could be a new strategy for optimizing the effects of physical training. However, this interpretation requires further research involving human subjects of different chronotypes.