Respiratory compensation and blood pH regulation during variable intensity exercise in trained versus untrained subjects

Abstract

To determine whether endurance-trained cyclists (T; n = 10) have a superior blood-respiratory buffering for metabolic acidosis relative to untrained subjects (UT; n = 10) during variable intensity exercise (VAR). On three occasions, T and UT pedaled for 24 min alternating high- and low-intensities as percentage of their second ventilatory threshold (VT2): VAR(LOW) 87.5-37.5% VT2, VAR(MODERATE) 125-25% VT2, and VAR(HIGH) 162.5-12.5% VT2 to complete the same amount of work. Before and just after each VAR trial, maximal cycling power (P(MAX)) was assessed. For each trial, the respiratory compensation for exercise acidosis (ventilatory equivalent for CO2) and the final blood pH, lactate and bicarbonate concentrations were similar for T and UT subjects. However, after VAR(HIGH), UT reduced P(MAX) (-14 +/- 1%; P < 0.05) while T did not. Our data suggest that endurance training confers adaptations to withstand the low pH provoked by VAR without losing cycling power, although this response is not due to differences in blood-respiratory buffering.

Validity and Reliability of Ventilatory and Blood Lactate Thresholds in Well-Trained Cyclists

“…For instance, VT 1 (i.e., anaerobic threshold; [ 28 ] is the intensity at which ventilation and VCO 2 increase in parallel. The increase expired CO 2 is generated by the HCO 3 - buffering of lactic acid that reaches the blood [ 29 ]. VT 2 (i.e., RCP, [ 28 ] in turn represents a work intensity at which blood lactate accumulation rises considerable and there is hyperventilation to buffer acidosis (i.e., ventilatory compensation).…”

Restoration of blood pH between repeated bouts of high-intensity exercise: effects of various active-recovery protocols

“…A progressively higher _ V E peak during several bouts of HIE could be induced by the progressive reduction in plasma pH that ensued during exercise. In a recent study, we have shown that ventilation during repeated bouts of HIE increases progressively as plasma pH falls below 7.35, despite maintaining exercise intensity constant (Coso et al 2009). On the other hand, a lower _ VCO 2 could be related to the progressive lower contribution of anaerobic pathways to the total energy expenditure as bouts were repeated (Dorado et al 2004).…”

“…4 bouts of intense exercise separated by 4.5 min of active-recovery), we have recently observed that blood lactate and H ? concentrations remain high during active-recovery periods even when exercising at 12% of subjects' respiratory compensation threshold [RCT; Coso et al (2009)]. This was the case despite that the active-recovery intensity used in this study (12% RCT was equivalent to 22% VT) was much lower than what is optimal when having 30 min of recovery after a single bout of intense exercise [i.e.…”

“…We chose these active-recovery intensities and durations because we have found that short-duration active-recovery (4.5 min at 12% RCT) does not allow reductions in blood H ? or lactate concentration despite stimulating respiratory compensation (Coso et al 2009). Using this criterion, we selected longer recovery periods (6 and 9 min for M EDIUM and L ONG ) compensated with lower exercise intensities.…”

“…In each assessment, subjects performed 3 all-out sprints lasting 4 s against the heavy Monark's Ò flywheel (21.5 kg) separated by 2 min of active recovery (50 W), as previously described (Coso et al 2009). The sprint with the highest power output was used for statistical analysis.…”