Acute moderate hypoxia affects the oxygen desaturation and the performance but not the oxygen uptake response.

The purpose of this study was to examine the influence of hypoxia on the O2 uptake response, on the arterial and muscular desaturation and on the test duration and test duration at VO2max during exhaustive exercise performed in normoxia and hypoxia at the same relative workload. Nine well-trained males cyclists performed an incremental test and an exhaustive constant power test at 90 % of maximal aerobic power on a cycling ergometer, both in normoxia and hypoxia (inspired O2 fraction = 16 %). Hypoxic normobar conditions were obtained using an Alti Trainer200 and muscular desaturation was monitored by near-infrared spectroscopy instrument (Niro-300). The mean response time (66 +/- 4 s vs. 44 +/- 7 s) was significantly lower in hypoxia caused by the shorter time constant of the VO2 slow component. This result was due to the lower absolute work rate in hypoxia which decreased the amplitude of the VO2 slow component. The arterial (94.6 +/- 0.3 % vs. 84.2 +/- 0.7 %) and muscular desaturation (in the vastus lateralis and the lateral gastrocnemius) were reduced by hypoxia. The test duration (440 +/- 31 s vs. 362 +/- 36 s) and the test duration at VO2max (286 +/- 53 s vs. 89 +/- 33 s) were significantly shorter in hypoxia. Only in normoxia, the test duration was correlated with arterial and muscular saturation (r = 0.823 and r = 0.828; p < 0.05). At the same relative workload, hypoxia modified performance, arterial and muscular oxygen desaturation but not the oxygen uptake response. In normoxia, correlation showed that desaturation seems to be a limiting factor of performance.

The effects of interval training on oxygen pulse and performance in supra-threshold runs.

The aim of this study was to examine (i) the effects of a severe interval training period on oxygen pulse kinetics (O2-p, the ratio between VO2 and heart rate), and (ii) to study the consequences of these effects on the variation of performance (time to exhaustion) during severe runs. Seven athletes were tested before and after an eight-weeks period of a specific intermittent training at v Delta 50, i.e., the intermediate velocity between the lactate threshold (vLT) and the velocity associated with VO2max (vVO2max ). During the test sessions, athletes performed an incremental test and an all-out test at the pretraining v Delta 50. After the training period they also completed an additional all-out test at the posttraining v Delta 50 (v Delta 50bis). Results showed that after training there was i) an increase in the O2-p maximal value during the incremental test (22.7 +/- 1.5 mlO2.b-1 vs. 20.6 +/- 1.5 mlO2.b-1; p < 0.04), ii) a decrease in the time to reach the O2-p steady state (TRO2-p ) at the same absolute v Delta 50 (33 +/- 7 s vs. 60 +/- 27 s; p < 0.04) and iii) an increase in the O2-p steady state duration (TSSO2-p) at the same absolute v Delta 50 (552 +/- 201 s vs. 407 +/- 106 s; p < 0.04). However, there was no relationship between the improvement of these two O 2 -p kinetics parameters (TRO2-p and TSS O2-p) and those of the performance. This study found that after an individualised interval-training program conducted at the same absolute velocity, the O2-p kinetics reached a steady state quicker and for a longer duration than before training. This is however not related with the improvement of performance.

Decrease of O(2) deficit is a potential factor in increased time to exhaustion after specific endurance training.

The main purpose of this study was to investigate the effects of an 8-wk severe interval training program on the parameters of oxygen uptake kinetics, such as the oxygen deficit and the slow component, and their potential consequences on the time until exhaustion in a severe run performed at the same absolute velocity before and after training. Six endurance-trained runners performed, on a 400-m synthetic track, an incremental test and an all-out test, at 93% of the velocity at maximal oxygen consumption, to assess the time until exhaustion. These tests were carried out before and after 8 wk of a severe interval training program, which was composed of two sessions of interval training at 93% of the velocity at maximal oxygen consumption and three recovery sessions of continuous training at 60--70% of the velocity at maximal oxygen consumption per week. Neither the oxygen deficit nor the slow component were correlated with the time until exhaustion (r = -0.300, P = 0.24, n = 18 vs. r = -0.420, P = 0.09, n = 18, respectively). After training, the oxygen deficit significantly decreased (P = 0.02), and the slow component did not change (P = 0.44). Only three subjects greatly improved their time until exhaustion (by 10, 24, and 101%). The changes of oxygen deficit were significantly correlated with the changes of time until exhaustion (r = -0.911, P = 0.01, n = 6). It was concluded that the decrease of oxygen deficit was a potential factor for the increase of time until exhaustion in a severe run performed after a specific endurance-training program.