The influence of posture and muscle contraction rate on the oxygenation status of the vastus lateralis while cycling

Among the factors that can influence the supply of blood and oxygen to the contracting skeletal muscle, the effects of posture and muscle contraction rate were investigated in this study. We hypothesized that the supine posture (SUP) would elicit less oxygenation of the vastus lateralis when cycling during moderate to intense exercise compared to upright posture (UP). In addition, we hypothesized that higher muscle contraction rate would be effective to minimize the desaturation of the vastus lateralis while cycling, and it would elicit a greater volume of oxygen uptake. A total 16 of participants were tested during upright and supine cycling at 60 RPM and 100 RPM. The four exercise intensities were calculated relative to their individual peak aerobic capacity during upright cycling. Near-infrared spectroscopy (NIRS) was applied to measure the concentrations of oxygenated hemoglobin (O₂Hb) and deoxygenated hemoglobin (HHb) of the vastus lateralis. In addition, pulmonary gas exchange (VO₂) and heart rate (HR) were measured. As a result, (HHb) was increased and % O₂ saturation was decreased as the exercise intensity increased (p<0.05). SUP elicited significantly higher (HHb) than UP (p<0.05), and less % O₂ saturation (p<0.001). A significant RPM effect was found in that 100 RPM elicited less of an increase of (HHb) comparing UP to SUP at a given moderate exercise intensity (p<0.05). Also, 100 RPM had significantly less of a drop of % O₂ saturation from UP to SUP at all exercise intensities (p<0.05). Especially at 70% of the VO₂peak, cycling in SUP 100 RPM maintained a significantly greater oxygen saturation compared to 60 RPM (p<0.05). In addition, 100 RPM elicited significantly greater volume of oxygen consumption than 60 RPM at each posture (p<0.001). In conclusion, as expected, the oxygen saturation of the skeletal muscle was significantly decreased as the exercise intensity increased. Furthermore, SUP elicited significantly less oxygen saturation of vastus lateralis than UP. Lastly, a higher muscle contraction rate can be effective in minimizing the oxygen desaturation of skeletal muscle while cycling at approximately 70% VO₂peak.