Influence of Fiber Type Composition and Capillary Density on Onset of Blood Lactate Accumulation

Abstract

Onset of blood lactate accumulation (OBLA) was determined in 16 healthy and physically active men (23-33 yrs) during cycling using a continuous stepwise increased exercise intensity protocol. OBLA was defined as the exercise intensity corresponding to a lactate concentration of 4 mmol · l^-1 blood. Oxygen consumption, pulmonary ventilation, respiratory quotient (R), heart rate, and lactate concentration were monitored during each exercise intensity. Muscle biopsies were obtained from m. vastus lateralis at rest for determination of fiber type composition and capillary density. Calculated values (mean ± SD) for exercise intensity, oxygen consumption and ventilation at OBLA were 159 (±37)W, 2.43 (±0.47) l·min^-1, and 49.8 (±10.5) l·min^-1 or 65(±10)% of V̇o_2max OBLA (% V̇o_2max) was found to correlate significantly (r = 0.75, P < 0.001) to the relative muscle area occupied by ST (type I) fibers. Furthermore, 92% of the variance in OBLA could be explained by% ST area + capillary density. It is suggested that both inherent and adaptative qualities of the exercising muscle are of significance for the onset of blood lactate accumulation.

Key words

fast- and slow-twitch fibers - m. vastus lateralis - oxygen consumption - percentage of V̇o_2max