EXERCISE-INDUCED CHANGES IN R-WAVE AMPLITUDE AND HEART-RATE IN NORMALSUBJECTS

An intermittent exercise protocol on a treadmill was used to examine s ix healthy subjects, and a steady protocol was applied to three of the subjects before and after short-term training. The peak blood velocit y in the common carotid artery increased by 73.1% during the intermitt ent protocol and recovered to resting level within 3 minutes, while th e heart rate (HR) remained high even 5 minutes after exercise. R wave amplitude (RWA) increased significantly from 1.40 +/- 0.39 mV at rest to 1.59 +/- 0.33 mV (P < .05) immediately after the start of walking, and decreased gradually to 1.46 +/- 0.36 mV (P < .05) during 3 minutes of walking. Thus, it decreased significantly to 1.31 +/- 0.40 mV (P < .01) during the interphase from exercise to rest, and increased again during recovery or rest periods in the intermittent protocol. The res ults suggest that an increase in the venous return per heart beat at t he start of walking induces the increase in RWA, and that its abrupt d ecrease at the end of walking induces the decrease in RWA. Subjects wi th a higher HR response and recovery slopes have smaller abrupt change s in RWA at the interphases between rest and walking. The gradual decr ease in RWA during walking may be related to a gradual increase in HR and a gradual decrease in systemic peripheral resistance, and the grad ual increase in RWA after walking may be related to a gradual decrease in HR and a gradual increase in systemic peripheral resistance.