Levelling-off of calf blood flow during walking and running, and its relationship to anaerobic threshold.

Abstract

Calf blood flow (CBF), heart rate (HR), whole-body VO2 were measured in 13 active women (aged 20.8 yrs) while walking or running at various speeds up to near exhaustion. CBF during walking increased linearly in relation to speed in the range 60-100 m/min, and thereafter it levelled off. CBF during running showed a small increase up to 180 m/min, then decreased significantly (p less than 0.01) from 24.51 ml/100 ml calf min to 19.62 ml/100 ml calf/min. VO2 corresponding to peak CBF (BFpeak-VO2) averaged 66.39% VO2-max, which was significantly lower (p less than 0.05) than the anaerobic threshold (AT; 74.48% VO2max) determined using gas exchange parameters. Significant correlation coefficients of 0.695 (p less than 0.01) and 0.708 (p less than 0.01) were obtained between BFpeak-VO2 and AT-VO2, and BFpeak-%VO2max and AT-%VO2max. The magnitude of CBF was not correlated significantly with AT or VO2max. Levelling-off or decrease of CBF at higher speeds, approximately 10% below AT, suggested that an inadequate blood supply will possibly result in mismatching between oxygen delivery and muscle oxygen demand and that this would lead to switching over to anaerobic energy generation.