Cardiac output and active limb blood flow responses to unilateral and bilateral dynamic handgrip exercise

The purposes of this study were 1) to determine cardiac output and active limb blood flow responses to unilateral and bilateral dynamic handgrip exercises and 2) to investigate the effects of exercise intensity and a change in active muscle mass on the relationship between limb blood flow and cardiac output. Five physically active women performed dynamic handgrip exercises with the right hand (right handgrip exercise ; RHG), with the left hand (left handgrip exercise ; LHG), and bilaterally (bilateral handgrip exercise ; BHG). Exercise intensities were 10%, 30% and 50% of the subjects' maximum voluntary contraction (MVC) and the exercise frequency was 60 contractions per minute. The 10%MVC exercise duration was 10 min, while the 30% and 50%MVC exercise conditions were performed to exhaustion. During exercise, stroke volume (SV) and heart rate (HR) were measured using Doppler ultrasound and electrocardiogram (ECG), respectively. Cardiac output (Q̇_sys) was calculated as the product of SV and HR. Blood flow to the forearm (Q̇_forearm) was measured by venous occlusion plethysmography. Q̇_sys did not differ significantly between RHG, LHG and BHG. However, SV was lower in BHG than in RHG and LHG. Reciprocally, HR was higher during BHG than RHG and LHG. The increase in the Q̇_forearm was significantly lower during BHG than RHG and LHG exercise (p<0.05). These results suggest that Q̇_sys does not differ between unilateral and bilateral handgrip exercise, despite the increase in active muscle mass. The unchanged Q̇_sys could be explained by the Q̇_forearm reduction during BHG. The Q̇_forearm was lower during BHG than during the unilateral hand-grip exercises, possibly due to vasoconstriction induced by BHG exercise.