Morning And Evening Effect Of Exercise On Circadian Rhythm Of Cardiac Hemodynamic And Autonomic Variables

Exercise as a modulator of circadian rhythm causes post exercise hypotension, the magnitude, and duration of this hypotensive effect are differ depending on many situations, including changes in the autonomic system. The purpose of this study is to evaluate the effect of morning and evening exercise on the circadian rhythm of heart hemodynamic and autonomic variables. 8 young healthy men (mean 32 ± 3 years old) attended the laboratory in 3 different sessions and performed an HIIE included 10 reps at 90% and 9 recoveries at 30% of VO2max in the morning (08:00) and evening (16:00) and a control. In all three sessions 24hr assessment of systolic, diastolic, and mean blood pressure was measured every 15 min (day) and every 45 min (night) and every 5 min for autonomic variables (nuLF، nuHF، nuLFHFR and VLF). The results showed that the BP changes after exercise are visible to 19hr and 20hr in the morning and evening, respectively (p<0.01). The average changes in BP in sleep, awake and 24hr assessment showed that the BP is significantly lower after exercise compared to the control trial (p<0.01). In addition, 3 to 8 hours after exercise in the morning and 5 to 6 hours after exercise in the afternoon post exercise hypotension occurred (p<0.05). In conclusion, exercise regardless of performing time of day has a lowering effect on hemodynamic variables. Furthermore, morning exercise had more impact on decreasing the BP during sleep, while evening exercise had more impact on awake and 24hr BP.