Blood flow in thigh muscle during bicycling exercise at varying work rates

Abstract

16 male subjects exercised at 25, 50, 75, 90, 100 and 120% of$\dot V_{O_2 \max }$ on a von Döbeln bicycle ergometer. The muscle mass was measured in a whole body counter. Muscle blood flow (MBF) estimated from the rate of¹³³Xe clearance from m. rectus femoris showed a levelling-off at about 0.5 l of blood per min and liter of muscle tissue (equal to an irrigation coefficient of 0.5 min⁻¹) at work rates above 50 to 60% of$\dot V_{O_2 }$. This concurs with clearance data from the literature. However, when MBF is calculated from$\dot V_{O_2 }$, muscle mass, and reliable values for$a - \upsilon _{O_2 }$ differences, MBF in the present subjects would: 1. Not level off before 90 to 100%$\dot V_{O_2 \max }$, 2. reach a value of 1.0 min⁻¹. The underestimation of MBF calculated from¹³³Xe clearance and the levelling-off shown by this method may be due to a systematic error inherent in the method, the¹³³Xe clearance being diffusion limited at high flow rates.