Cardiorespiratory Responses and Mechanical Efficiency During Repeated Isokinetic Extension-Flexion Exercises of the Upper and Lower Limbs

Abstract

This study compared cardiorespiratory responses and mechanical efficiency in the upper (UL) and lower (LL) limbs during repeated isokinetic extension-flexion exercise. Eight healthy male university students served as subjects. Each subject performed UL and LL exercises on separate days. The exercise consisted of three sets of maximal isokinetic extension-flexion actions at the elbow or the knee joints for 30 seconds at a speed of 180 degrees per second with a 30-second interval between sets. Heart rate (HR), oxygen uptake (Vo₂), carbon dioxide production (Vco₂), pulmonary ventilation (V_E), and respiratory rate (RR) were measured during and after exercise. From these measurements, tidal volume (V_T), ventilation equivalent (V_E/Vo₂), O₂pulse, net O₂requirement, and net mechanical efficiency were calculated. The volume of the upper arm and the thigh were determined with a water displacement method. The Vo₂, Vco₂, V_E, V_T, and HR during LL exercise were significantly higher (p<.05 to p<.001) than during UL exercise. The O₂pulse and V_E/Vo₂during UL exercise were significantly lower (p<0.01 and p<0.05) than during LL exercise. Limb volume was significantly (p<0.01 to p<0.001) correlated with Vo₂and mechanical efficiency. These results suggest that the lesser cardiorespiratory responses during UL exercise are related to the smaller muscle mass. Mechanical efficiency was also lower in UL exercise than during LL exercise. It seemed that not only the smaller muscle mass of the arm but also involvement of a greater static component and higher anaerobic metabolism during UL exercise contributed to the lower mechanical efficiency of UL exercise.