ABSTRACT
The change in R-R interval (RRI) induced by rapid postural change from a squat posture to standing was analyzed in 8 healthy male students (20.3±1.2 years of age) before and immediately after maximal running exercise. We instructed subjects to stand up as quickly as possible, and to repeat the standing-up movement three times at intervals of 2 min. Heart rate responses and heart rate variability were analyzed by the change in RRI induced by standing up. Heart rate (HR) increased quickly at the onset of standing up. The time (T) until the maximal HR (Hmax) was reached 9.79±1.44 s after standing up, and then the HR after Hmax decreased rapidly with time. The maximal HR was 1.20 times higher while standing up than in the squat position. Maximal running exercise significantly delayed the time taken to reach Hmax after standing up, and significantly diminished the increased HR to 1.15 times. The Hmax/Hmin ratio, which expressed the magnitude of autonomic activity during standing up, was significantly lower following maximal exercise, indicating that the cardiac sympathetic nervous system seems to be in a state of hyperfunction immediately after maximal running exercise. These findings suggest that disturbance in the postural adjustment of the cardiovascular system immediately after intense exercise may be induced by the delayed response and decreased amplitude of the HR.