Is the Slow Component of Exercise $(\dot V{o_2})$ a Respiratory Adaptation to Anaerobiosis?

Abstract

The increased rate of O₂ consumption $(\dot V{o_2})$ during exercise reflects the rate of aerobic regeneration of adenosine triphosphate (ATP). In 1972, Whipp and Wasserman (9) reported that a steady-state for aerobic regeneration occurred by 3 minutes only for work rates below the lactic acidosis threshold (LAT).For work rates above the LAT, $\dot V{o_2}$ continued to increase past 3 minutes, the rate quantified as the $\dot V{o_2}$ increase between 3 and 6 minutes ($\Delta \dot V{o_2}$(6–3)). $\Delta \dot V{o_2}$(6–3) has a high linear correlation with blood lactate increase with the regression passing through the origin (8). Others (summarized in ref 8) have confirmed an association between blood lactate increase and the slow component, but a causal mechanism remains unclear. The slow component increase in $\dot V{o_2}$, as illustrated in figure 1, could reflect either 1) a developing inefficiency in the aerobic regeneration of ATP, 2) an adaptation to an anaerobic state in which the O₂, supply to the muscles was improving, thereby facilitating the aerobic regeneration of ATP, or 3) a combination of both processes.