Lactate and ventilatory thresholds: Disparity in time course of adaptations to training

We tested the hypothesis that the lactate threshold (T(lac)) during incremental exercise could be increased significantly during the first 3 wk of endurance training without any concomitant change in the ventilatory threshold (T(vent)). T(vent) is defined as O₂ uptake (V̇O₂) at which ventilatory equivalent for O₂ [expired ventilation per V̇O₂ (V̇E/V̇O₂)] increased without a simultaneous increase in the ventilatory equivalent for CO₂ (V̇E/V̇CO₂). Weekly measurements of ventilatory gas exchange and blood lactate responses during incremental and steady-state exercise were performed on six subjects (4 male; 2 female) who exercised 6 days/wk, 30 min/session at 70-80% of pretraining V̇O₂(max) for 3 wk. Pretraining T(lac) and T(vent) were not significantly different. After 3 wk of training, significant increases (P < 0.05) occurred for mean (± SE) V̇O₂(max) (392 ± 103 ml/min) and T(lac) (482 ± 135 ml/min). T(vent) did not change during the 3 wk of training, despite significant (P < 0.05) reductions in V̇E responses to both incremental and steady-state exercise. Thus ventilatory adaptations to exercise during the first 3 wk of exercise training were not accompanied by a detectable alteration in the ventilatory 'threshold' during a 1-min incremental exercise protocol. The mean absolute difference between pairs of T(lac) and T(vent) posttraining was 499 ml/min. Despite the significant training-induced dissociation between T(lac) and T(vent) a high correlation between the two parameters was obtained posttraining (r = 0.86, P < 0.05). These results indicate a coincidental rather than causal relationship. For improvements in T(lac) documented to occur after many weeks or months of training, the results of this investigation suggest that the rate of change in T(lac) is fastest during the first 2-3 wk of training.