Abstract
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 ( SmO2 ), oxygen consumption ( V̇O2 ) 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, SmO2 , V̇O2 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, SmO2 , V̇O2 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 SmO2 (-38 ± 23 vs. -21% ± 18%, P < 0.001) were greater than upright, while the increase in V̇O2 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 V̇O2 . Further work is required to understand the effects of a semi-upright exercise position on skeletal muscle activation and lower limb blood flow.