Influence of training on sleeping heart rate following daytime exercise

The purpose of this investigation was to examine the influence of daytime exercise on heart rate during sleep. Nine, untrained male college students volunteered to participate. They cycled at 75% maximum oxygen uptake, (VO2max) 30 min.day-1 for 12 weeks. The exercise duration was increased by 5 min every 4 weeks from 30 to 40 min per session. Post-training VO2max [mean (SE): 48.9 (1.7) ml.kg-1.min-1] values were significantly (P < 0.01) higher than pre-training [45.5 (1.8) ml.kg-1.min-1] values. Before and after training, sleeping heart rate was assessed on two separate nights. Data were obtained during a night following 30 min of daytime cycling at 75 (6) % VO2max and on a night in which no daytime exercise was performed. A three-way repeated measures ANOVA [training status (pre-/post-training) x activity (exercise day/nonexercise day) x sleep time (18 epochs of 20 min each)] revealed a significant main effect for sleep time (P < 0.001) as well as a sleep time x training status interaction (P < 0.02). No significant difference in sleeping heart rate was noted when exercise and non-exercise days were compared both before and after training. It is concluded that endurance training in these young adult men: (1) hastens the achievement of baseline heart rate during sleep, and (2) does not moderate the relationship between an acute bout of daytime exercise and sleeping heart rate.