Prior moderate and heavy exercise accelerate oxygen uptake and cardiac output kinetics in endurance athletes

Abstract

Cardiorespiratory interactions at the onset of dynamic cycling exercise are modified by warm-up exercises. We tested the hypotheses that oxygen uptake (V̇o2) and cardiac output (Q̇) kinetics would be accelerated at the onset of heavy and moderate cycling exercise by warm-up. Nine male endurance athletes (peak V̇o2: 60.5 ± 3.2 ml·min−1·kg−1) performed multiple rides of two different 36-min cycling protocols, involving 6-min bouts at moderate and heavy intensities. Breath-by-breath V̇o2and beat-by-beat stroke volume (SV) and Q̇, estimated by Modelflow from the finger pulse, were measured simultaneously with kinetics quantified from the phase II time constant (τ2). One novel finding was that both moderate (M) and heavy (H) warm-up bouts accelerated phase II V̇o2kinetics during a subsequent bout of heavy exercise (τ2: after M = 22.5 ± 2.7 s, after H = 22.1 ± 2.9 vs. 26.2 ± 3.2 s; P < 0.01). Q̇ kinetics in heavy exercise were accelerated by both warm-up intensities (τ2: M = 22.0 ± 4.1 s, H = 23.8 ± 5.6 s vs. 27.4 ± 7.2 s; P < 0.05). During moderate exercise, prior heavy-intensity warm-up (one or two bouts) accelerated V̇o2kinetics and elevated Q̇ at exercise onset, with no changes in Q̇ kinetics. A second novel finding was a significant overshoot in the estimate of SV from Modelflow in the first minutes of each moderate and heavy exercise bout. These findings suggest that the acceleration of V̇o2kinetics during heavy exercise was enabled by the acceleration of Q̇ kinetics, and that rapid increases in Q̇ at the onset of moderate and heavy exercise might result, in part, from an overshoot of SV.