Effects of exercise‐induced arterial hypoxaemia and work rate on diaphragmatic fatigue in highly trained endurance athletes

Abstract

Diaphragmatic fatigue occurs in highly trained athletes during exhaustive exercise. Since approximately half of them also exhibit exercise-induced arterial hypoxaemia (EIAH) during high-intensity exercise, the present study sought to test the hypothesis that arterial hypoxaemia contributes to exercise-induced diaphragmatic fatigue in this population. Ten cyclists (V O 2 max : 70.0 ± 1.6 ml kg -1 min -1 ; mean ± S.E.M.) completed, in a balanced ordering sequence, one normoxic (end-exercise arterial O 2 saturation (S a,O 2 ): 92 ± 1%) and one hyperoxic (F I,O 2 : 0.5% O 2 ; S a,O 2 : 97 ± 1%) 5 min exercise test at intensities equal to 80 ± 3 and 90 ± 3% of maximal work rate (WR max ), respectively, producing the same tidal volume (V T ) and breathing frequency (f ) throughout exercise. Cervical magnetic stimulation was used to determine reduction in twitch transdiaphragmatic pressure (P di,tw ) during recovery. Hyperoxic exercise at 90% WR max induced significantly (P = 0.022) greater post-exercise reduction in P di,tw (15 ± 2%) than did normoxic exercise at 80% WR max (9 ± 2%), despite the similar mean ventilation (123 ± 8 and 119 ± 8 l min -1 , respectively), breathing pattern (V T : 2.53 ± 0.05 and 2.61 ± 0.05 l, f : 49 ± 2 and 46 ± 2 breaths min -1 , respectively), mean changes in P di during exercise (37.1 ± 2.4 and 38.2 ± 2.8 cmH 2 O, respectively) and end-exercise arterial lactate (12.1 ± 1.4 and 10.8 ± 1.1 mmol l -1 , respectively). The difference found in diaphragmatic fatigue between the hyperoxic (at higher leg work rate) and the normoxic (at lower leg work rate) tests suggests that neither EIAH nor lactic acidosis per se are likely predominant causative factors in diaphragmatic fatigue in this population, at least at the level of S a,O 2 tested. Rather, this result leads us to hypothesize that blood flow competition with the legs is an important contributor to diaphragmatic fatigue in heavy exercise, assuming that higher leg work required greater leg blood flow.

Exercise-induced arterial hypoxemia in aerobic and anaerobic trained athletes during incremental exercise

“…Powers et al shown the difference % SaO 2 between resting and at the 100% VO 2max ranged from 4% in one subject to 16% in another [31]. On the other hand, it appear that the mean SaO 2 values in our study are lower than have been reported in some previous studies [14][15][16][17] yet are similar to those from others [6,8,30,31]. The degree of EIAH is affected the muscle mass engagement in the exercise and the exercise modality [16,32].…”

“…Previous studies have shown a greater drop in the SaO 2 at both maximal and sub-maximal exercise during treadmill running compared with ergometer cycling [16,33]. In the present study, we used incremental treadmill exercise while some studies used incremental exercise on cycle ergometers that have displayed higher [13][14][15][16][17]. Differences of exercise modality and protocol types used may help to explain the differences in SaO 2 measured.…”

“…Studies examining EIAH have primarily focused on aerobic trained individuals [4,8,[12][13][14][15][16][17][18]. Interestingly, no studies have examined the EIAH in anaerobic trained athletes.…”

Ventilation and Respiratory Mechanics

“…The most likely reason why the diaphragm's fatigue threshold of force output is lower during exercise than at rest is that at rest the volitional increases in diaphragmatic force output are probably met by an adequate blood flow supply to the diaphragm, whereas during exercise there may be competition for blood flow between the diaphragm and locomotor muscles (210,212). This imbalance of diaphragmatic force output and O 2 transport to the diaphragm occurs most consistently when endurance exercise elicits at least 80% to 85%V o 2 max (246, 328) or less than 85% Sao 2 (44,545,546).…”

Exercise-induced respiratory muscle fatigue: implications for performance

“…In healthy young adults of varying fitness, an imbalance of muscle force output versus blood flow or O 2 transport availability to the diaphragm that favors fatigue appears to occur most consistently when the intensity of prolonged endurance exercise elicits at least 80 -85% of V O 2max (52) or arterial O 2 saturation drops below ϳ85% (10,135,136).…”