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.

The present purpose was to study the relationships between perceived exertion (RPE, ETL) and exercise duration for all-out runs eliciting vVO2 max. 12 endurance-trained men performed three exhausting exercises on an indoor track. The first test was an incremental exercise to measure their maximal oxygen uptake (VO2 max), the velocity associated with VO2 max (vVO2 max), the velocity of the lacate concentration threshold (vLT) and the velocity delta 50 (vdelta50: the velocity halfway between vVO2 max and vLT). The second and third tests were a constant load all-out run at vVO2 max and vdelta50 to measure the time to exhaustion at these intensities (tlim vVO2 max and tlim vdelta50, respectively). vdelta50 corresponded to 90.1 +/- 2.5% vVO2 max; tlim vVO2 max and tlim vdelta50 were equal to 286 +/- 71 sec. and 547+/- 157 sec., respectively. For a same given relative time (%tlim), athletes perceived exercise as harder and felt that they could endure less for vVO2 max than vdelta50. When subjects began to perceive exercise as "hard" (RPE = 15), they had run for only 36.4 +/- 26.8%tlim at vVO2 max, whereas they had run for 46.1 +/- 15.7 %tlim at vdelta50. These results indicate that RPE and ETL scales were a combined subjective estimation of both intensity and exercise duration for all-out runs at 90 and 100% vVO2 max. Therefore, this scale could be used to assess duration as well as intensity of exercise for the practical application in sport. Moreover, it could be suggested that exercise duration can be prescribed as a function of perceived exertion for healthy normal people. Consequently, perceived exertion could be an important tool to individualize the prescription of a training program.

The question of cardiac strain arises when considering the emerging class of recreational runners whose running strategy could be a non-optimal running pace. Heart rate (HR) monitoring, which reflects exercise intensity and environmental factors, is often used for running strategies in marathons. However, it is difficult to obtain appropriate feedback for only the HR value since the cardiovascular drift (CV drift) occurs during prolonged exercise. The cardiac cost (CC: HR divided by running velocity) has been shown to be a potential index for evaluation of CV drift during the marathon race. We sought to establish the relationship between recreational marathoners' racing strategy, cardiac drift, and performance. We started with looking for a trend in the speed time series (by Kendall's non-parametric rank correlation coefficient) in 280 (2 h30-3 h40) marathoners. We distinguished two groups, with the one gathering the large majority of runners (n = 215, 77%), who had a significant decrease in their speed during the race that appeared at the 26th km. We therefore named this group of runners the "fallers." Furthermore, the fallers had significantly lower performance (p = 0.006) and higher cardiac drift (p < 0.0001) than the non-fallers. The asymmetry indicator of the faller group runners' speed is negative, meaning that the average speed of this category of riders is below the median, indicating that they ran more than the half marathon distance (56%) above their average speed before they "hit the wall" at the 26th km. Furthermore, we showed that marathon performance was correlated with the amplitude of the cardiac drift (r = 0.18, p = 0.0018) but not with those of the increase in HR (r = 0.01, p = 0.80). In conclusion, for addressing the question of the cardiac drift in marathon, which is very sensitive to the running strategy, we recommend to utilize the cardiac cost, which takes into account the running speed and that could be implemented in the future, on mobile phone applications.

No abstract