Morning or evening training : effect on heart rate circadian rhythm

Twenty male endurance athletes (aged 20–25 years) carried out 2-hour daily training sessions, every day from Monday to Friday, for an overall period of 4 weeks. Four different weekly training time table (09.00-11.00; 11.00-13.00; 16.00-18.00; 18.00-20.00 hours) were followed, changing the time slot each week. Each athlete trained, in turn, in each period. The fifth day of each week, heart rate was monitored for 24-28 hours. Statistical analysis employed the single and mean cosinor methods. The heart rate (HR) circadian rhythm was statistically significant (p<0.05) in all 4 training session time. The HR acrophase is progressively postponed during the afternoon: the heart rate acrophase for training done between 18.00 and 20.00 is delayed by approximately 3 hours compared to that of the training done between 09.00 and 11.00. Training done at different daily times synchronizes the HR circadian rhythm. Temporal programming of physical activity is a tool capable of modifying the temporal structure of physiological variables. This approach can be of great interest for coaches who plan training programs and it may benefit athletes when time zone adjustment is an issue, such as transferring to a different continent for a competitive event.