Day-to-day changes in oxygen uptake kinetics at the onset of exercise during strenuous endurance training

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Abstract
The aim of this study was to assess the effect of strenuous endurance training on day-to-day changes in oxygen uptake (VO2) on-kinetics (time constant) at the onset.of exercise. Four healthy men participated in strenuous training, for 30 min·day−1, 6 days·week−1 for 3 weeks. The VO2 was measured breath-by-breath every day except Sunday at exercise intensities corresponding to the lactate threshold (LT) and the onset of blood lactate accumulation (OBLA) which were obtained before training. Furthermore, an incremental exercise test was performed to determine LT, OBLA and maximal oxygen uptake (VO2max) before and after the training period and every weekend. The 30-min heavy endurance training was performed on a cycle ergometer 5 days·week−1 for 3 weeks. Another six men served as the control group. After training, significant reductions of the VO2 time constant for exercise at the pretraining LT exercise intensity (PP2 time constants in the control group did not change significantly. A high correlation between the decrease in the VO2 time constant and training day was observed in exercise at the pretraining LT exercise intensity (r=−0.76; Pr= −0.91; P2 at LT, VO2 at OBLA and VO2max increased significantly after training (P2 on-kinetics may be observed. This may be explained. by some effect of blood lactate during exercise on VO2 on-kinetics, together with significantly improved cardiovascular kinetics at the onset of exercise.