Effect of hyperventilation and prior heavy exercise on O₂ uptake and muscle deoxygenation kinetics during transitions to moderate exercise

摘要

The effect of hyperventilation-induced hypocapnic alkalosis (HYPO) and prior heavy-intensity exercise (HVY) on pulmonary O₂ uptake kinetics were examined in young adults (n = 7) during moderate-intensity exercise (MOD). Subjects completed leg cycling exercise during (1) normal breathing (CON, P_ETCO₂ ~ 40 mmHg) and (2) controlled hyperventilation (HYPO, P_ETCO₂ ~ 20 mmHg) throughout the protocol, with each condition repeated on four occasions. The protocol consisted of two MOD transitions (MOD1, MOD2) to 80% estimated lactate threshold with MOD2 preceded by HVY (Δ50%); each transition lasted 6 min and was preceded by 20 W cycling. was measured breath-by-breath and concentration changes in oxy- and deoxy-hemoglobin/myoglobin (Δ[HHb]) of the vastus lateralis muscle were measured by near-infrared spectroscopy. Adjustment of and Δ[HHb] were modeled using a mono-exponential equation by non-linear regression. During MOD1, the phase 2 time constant (τ) for was greater (P < 0.05) in HYPO (45 ± 24 s) than CON (28 ± 17 s). During MOD2, was reduced (P < 0.05) in both conditions (HYPO: 24 ± 7 s, CON: 20 ± 8 s). The Δ[Hb_TOT] and Δ[O₂Hb] were greater (P < 0.05) prior to and throughout MOD2. The Δ[HHb] mean response time was similar in MOD1 and MOD2, and between conditions, however, the MOD1 Δ[HHb] amplitude was greater (P < 0.05) in HYPO compared to CON, with no differences between conditions in MOD2. These findings suggest that the speeding of kinetics after prior HVY in HYPO was related, in part, to an increase in microvascular perfusion.