Maximal voluntary hyperpnoea increases blood lactate concentration during exercise

Ventilatory work during heavy endurance exercise has not been thought to influence systemic lactate concentration. We evaluated the effect of maximal isocapnic volitional hyperpnoea upon arterialised venous blood lactate concentration ([lac⁻]_B) during leg cycling exercise at maximum lactate steady state (MLSS). Seven healthy males performed a lactate minimum test to estimate MLSS, which was then resolved using separate 30 min constant power tests (MLSS=207±8 W, mean ± SEM). Thereafter, a 30 min control trial at MLSS was performed. In a further experimental trial, the control trial was mimicked except that from 20 to 28 min maximal isocapnic volitional hyperpnoea was superimposed on exercise. Over 20–28 min minute ventilation, oxygen uptake, and heart rate during the control and experimental trials were 87.3±2.4 and 168.3±7.0 l min⁻¹ (P<0.01), the latter being comparable to that achieved in the maximal phase of the lactate minimum test (171.9±6.8 l min⁻¹), 3.46±0.20 and 3.83 ± 0.20 l min⁻¹ (P<0.01), and 158.5±2.7 and 166.8±2.7 beats min⁻¹ (P<0.05), respectively. From 20 to 30 min of the experimental trial [lac⁻]_B increased from 3.7±0.2 to 4.7±0.3 mmol l⁻¹ (P<0.05). The partial pressure of carbon dioxide in arterialised venous blood increased approximately 3 mmHg during volitional hyperpnoea, which may have attenuated the [lac⁻]_B increase. These results show that, during heavy exercise, respiratory muscle work may affect [lac⁻]_B. We speculate that the changes observed were related to the altered lactate turnover in respiratory muscles, locomotor muscles, or both.