At equivalent power output and oxygen uptake, the heart rate in the arm cranking is higher than that in leg cyling but the stroke volume in the arm cranking is lower than that of the leg cycling. However, little is known for the transient changes of these param-eters. In particular, there are few data on the early transient changes (phase I) in oxygen uptake (Vo₂) and heart rate (HR) and the relationship between the kinetics of these parameters and work rate in the arm cranking. Since the arm exercise at steady state decreases venous return and increases anaerobic glycolytic response, it is considered that an increase in Vo₂ in phase I of the arm exercise would be small and that of the phase II would prolong.
　To test this hypothesis, the time dependent change in Vo₂ and HR were measured when the intensity of the arm cranking was increased from rest to the constant work (25, 37 and 50) and it was compared to those in the leg exercise. Gas exchange and HR were measured breath by breath in 5 male subjects. The increase in Vo₂ and HR in the phase I of the arm cranking and leg cycling had good correlation with work rate. The increase in Vo₂ in the phase I of the arm exercise was lower than that of the leg exercise, suggesting that the immediate adjustment of cardiac output to the arm exercise was impaired. The significant difference of Vo₂ response in phase I to different types of exercise may reflect the difference of the rate and volume of venous return which due to the muscle exercised, the different degree of vasoconstriction and the effect of higher intrathoracic pressure. An increase in HR in the arm exercise was higher than that in the leg exercise and this suggested that an increase in Vo₂ / HR in this phase of the arm exercise was lower than that of the leg exercise. The results indicate that an increase in the stroke volume of the arm exercise might be attenuated. The kinetics of Vo₂ response in the arm exercise prolonged compared to that in the leg exercise at the same work rate.
　The difference might be explained by a decreased venous return and higher anaerobic glycolysis which occurs early stage of the arm exercise associated with isometric exercise and a greater recruitment of fast twitch motor units. These findings provide useful information to explain the kinetics of gas exchange in arm exercise.

DESCENTE SPORTS SCIENCE Vol.13/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE