Cardiac output decline in prolonged dynamic exercise is affected by the exercise mode

The aim of this study was to compare the cardiovascular responses to prolonged submaximal cycling and running. Eleven males [maximal oxygen uptake (V̇O_2max): 3.58±0.15 l min^-1 for running and 3.84±0.16 l min^-1 for cycling; mean±SE] either cycled (C) or ran (R) for 90 min at 60% of mode-specific V̇O_2max, on two randomly assigned occasions. Cardiac output declined after 85 min of exercise in C (-1.9±0.5 l min^-1, P<0.01) but not in R, as a result of a more pronounced decrease in stroke volume in the former exercise mode (-22.7±3.8 ml beat^-1 vs -14.3±1.9 ml beat^-1, P<0.01) since heart rate did not differ between trials. Stroke volume responses were despite a higher level of dehydration (-3.3±0.2% in R vs -2.8±0.2% in C, P<0.05) and hyperthermia in R (39.6±0.1 vs 38.8±0.1°C in C at 90 min, P<0.01). Finally, mean skin blood flow was lower in R than C (72±8 vs 89±10%; P<0.05). In conclusion, stroke volume and cardiac output decline was more pronounced in cycling than in running despite lower dehydration and rectal temperature in the former exercise mode.