Overshoot in V̇O₂ following the onset of moderate-intensity cycle exercise in trained cyclists

Abstract

We have previously observed that following the onset of moderate intensity cycle ergometry, the pulmonary O₂ uptake (V̇O₂) in trained cyclists often does not increase towards its steady-state value with the typical mono-exponential characteristics; rather, there is a transient “overshoot”. The purpose of this study was to systematically examine this phenomenon by comparing the V̇O₂responses to two moderate-intensity work rates and one high-intensity work rate in trained and untrained subjects. Following a ramp exercise test to the limit of tolerance for the determination of the gas exchange threshold (GET) and V̇O_2peak, seven trained cyclists [mean (SD); V̇O_2peak 66.6 (2.5) ml·kg⁻¹·min⁻¹] and eight sedentary subjects [V̇O_2peak 42.9 (5.1) ml·kg⁻¹·min⁻¹] completed six step transitions from baseline cycling to work rates requiring 60% and 80% GET and three step transitions from baseline cycling to a work rate requiring 50% of the difference between GET and V̇O_2peak (50%Δ). V̇O₂ was measured breath-by-breath and modelled using standard techniques. The sedentary subjects did not overshoot the steady-state V̇O₂ at any intensity. At 60% GET, six of the seven cyclists overshot the steady-state V̇O₂ [by an integral volume of 164 (44) ml between ~45 and 125 s]. At 80% GET, four of the seven cyclists overshot the steady-state V̇O₂ [by an integral volume of 185 (92) ml between ~55 and 140 s]. None of the cyclists showed an overshoot at 50%Δ. These results indicate that trained cyclists evidence an overshoot in V̇O₂ before steady-state is reached in the transition to moderate-intensity exercise. The mechanism(s) responsible for this effect remains to be elucidated, as does whether the overshoot confers any functional or performance benefit to the trained cyclist.