The effect of body position on cardiovascular, skeletal muscle and ventilatory responses to submaximal cycling

The completion of exercise in different body positions can impact the function of various components of the oxygen delivery pathway; however, the effect of the haemodynamic conditions induced by a semi-upright body position on the integrative physiological response to exercise is poorly understood. The purpose of this study was to explore the effect of a semi-upright body position on cardiac output (CO), vastus lateralis oxygen saturation ( $S_{m{O}_2}$ ), oxygen consumption ( ${\dot{V}}_{O_2}$ ) and ratings of perceived exertion (Borg RPE) during submaximal cycling. Twenty healthy individuals (22 ± 3 years, 50% female) each completed alternating 5-min bouts of submaximal upright and semi-upright (40° incline) cycling at 50 and 100 W. CO, $S_{m{O}_2}$ , ${\dot{V}}_{O_2}$ and RPE were assessed at rest and at each exercise intensity during steady state. There was a main effect of intensity on the increase in CO, $S_{m{O}_2}$ , ${\dot{V}}_{O_2}$ and RPE (all P < 0.001). In a semi-upright position, the increase in CO (7.9 ± 2.8 vs. 6.4 ± 2.6 L/min, P < 0.001), RPE (median (interquartile range): 11 (9-13) vs. 10 (8-12), P = 0.013) and the decrease in $S_{m{O}_2}$ (-38 ± 23 vs. -21% ± 18%, P < 0.001) were greater than upright, while the increase in ${\dot{V}}_{O_2}$ was attenuated (1.030 ± 0.130 vs. 1.154 ± 0.165 L/min, P < 0.001). These results suggest that while a semi-upright body position produces elevations in CO, these elevations do not seem to perfuse the active skeletal muscle. This may explain the elevation in RPE despite a blunting in the increase in ${\dot{V}}_{O_2}$ . Further work is required to understand the effects of a semi-upright exercise position on skeletal muscle activation and lower limb blood flow.