Relationship between pedaling rate and physiological responses during passive leg cycling

The purpose of this study was to investigate the influences of pedaling rate during passive leg cycling (PLC) on respiratory and cardiac responses in able-bodied subjects. Ten male and ten female subjects performed PLC on an electric motor-controlled ergometer that provides constant-rate pedaling. After PLC at 20 rpm for 5 min, the pedaling rate was gradually increased by 5 rpm every 1 min until 70 rpm was attained. Gas exchange responses, heart rate, and muscle oxygenation were measured during rest and PLC. The increases in ventilation, oxygen uptake, and heart rate in both sexes accelerated when the pedaling rate exceeded a threshold of between 20-45 rpm. Over this threshold, they increased linearly, not exponentially. These results suggest that respiratory and cardiac responses were influenced by the pedaling rate during PLC and were promoted at a low pedaling rate.