VO2 OVERSHOOTS THE STEADY-STATE VALUE IN THE TRANSITION TO MODERATE EXERCISE IN TRAINED CYCLISTS

Abstract

We have previously observed that some trained subjects evidence an “overshoot” in VO2 at the onset of moderate-intensity exercise. PURPOSE To systematically examine this phenomenon by comparing the VO2 responses to two moderate-intensity work rates in trained and untrained subjects. METHODS Seven trained cyclists (mean ± SD; age 20 ± 2 years, body mass 66.7 ± 6.4 kg, VO2 peak 66.6 ± 2.5 ml·kg−1 min−1) and eight sedentary subjects (age 21 ± 2 years, body mass 73.6 ± 6.7 kg, VO2 peak 42.9 ± 5.1 ml·kg−1·min−1) gave written informed consent to participate in this ethically approved study. Following a ramp exercise test to volitional exhaustion for the determination of the ventilatory threshold (VT) and VO2 peak, subjects completed 6 square-wave transitions from unloaded cycling to work rates requiring 60% of the subjects' VT (60%VT) and 80% of the subjects' VT (80%VT), and 3 square-wave transitions to 50% of the difference between VT and VO2 peak (50%Δ). VO2 was measured breath-by-breath and modelled using standard techniques. RESULTS The sedentary subjects did not overshoot the steady-state VO2 at any intensity. At 60% VT, 6 of the 7 cyclists “overshot” the steady-state VO2 (by 164 ± 44 ml between ∼45 and 125 s). At 80% VT, 4 of the 7 cyclists “overshot” the steady-state VO2 (by 185 ± 92 ml between ∼55 and 140 s). At 50%Δ, none of the cyclists evidenced an overshoot. Overshoots in VO2 were generally associated with overshoots in heart rate. CONCLUSION These results indicate that trained cyclists evidence an overshoot in VO2 before steady-state is reached in the transition to moderate-intensity exercise. The mechanism responsible for this effect is unclear but differences in motor unit recruitment or circulatory adjustment in trained compared to untrained subjects may be responsible.