Effects Of Aerobic Fitness On Blood Buffering And Maximal Cycling Power During Variable Intensity Exercise.

Abstract

Variable intensity exercise (VAR = short bouts of high-intensity exercise followed by low intensity for recovery) is typically used by aerobically-trained (AET) and untrained people (UT) to improve endurance performance. However VAR lowers blood pH which is associated with reductions in muscle force. PURPOSE: To determine if acid-base regulation during VAR differs between UT and AET and its effects on maximal cycling power. METHODS: Ten AET and ten UT (= 64 ± 6 vs 55 ± 6 mL·kg-1·min-1; P < 0.05) pedaled alternating high (1.5 min) with low (4.5 min) exercise intensity for 24 min. Exercise intensity was normalized to their ventilatory threshold (VT) resulting in 3 trials; VARLOW = 87.5-37.5% VT; VARMODERATE, 125-25% VT; and VARHIGH 162.5-12.5% VT. Total work was the same for all trials (213 ± 8 and 149 ± 23 kJ for AET and UT). Arterialized-blood samples and expired gas were obtained during exercise and maximal cycling power (PMAX) was measured prior and after exercise. RESULTS:Table 1 shows the mean ± SD for blood pH (pHblood) and bicarbonate concentration ([HCO3-]blood), ventilatory equivalent for CO2 (VE · VCO2-1) and change in PMAX at the end of each protocol. * Different from VARLOW at P < 0.05. † Different from VARMODERATE at P < 0.05. ‡ Different from AET at P < 0.05TABLECONCLUSIONS: To increase the exercise intensity during VAR produced similar decrease in blood pH and bicarbonate concentration and comparable increase in the respiratory compensation between AET and UT. This suggests that blood-respiratory buffering systems are not impaired in UT people during VAR. However, despite similar low blood pH, only UT reduced the maximal cycling power after VARHIGH. Thus, training may confer adaptations to withstand low pH without loosing neuromuscular power.