Feed-forward regulation of self-selected exercise intensity in response to different rates of arterial deoxygenation

Abstract

Arterial desaturation impairs exercise performance in a dose-dependent manner. However, new theories of exerciseinduced fatigue suggest that increasing rates of arterial deoxygenation augment the fatigue response during exercise. The purpose of this dissertation is to clarify if self-selected exercise intensity, while exercising at a constant rate of perceived exertion (RPE), is sensitive to alterations in the absolute arterial saturation (S P O 2 ) and/or the rate of change in S P O 2 . Subjects performed constant RPE exercise for 30 min. They were instructed to adjust their exercise intensity during the trial to maintain their RPE at 5 on Borg's 10-point scale. Subjects engaged in continuous bilateral, isokinetic cycling and intermittent, unilateral, isometric knee-extension. The fraction of inspired oxygen was reduced to desaturate arterial blood from starting values (>98%) to 70%. This desaturation occurred linearly over 3 target time periods (FAST, 5 min; MED, 15 min; SLOW, 25 min). The rate of arterial desaturation was significantly different between each of the 3 conditions. During cycling exercise, PO (FAST = 2.8 ± 2.1 W·% S P O 2 −1 ; MED = 2.5 ± 1.8 W·% S P O 2 −1 ; SLOW = 1.8 ± 1.6 W·% S P O 2 −1 ; P < 0.001) and surface electromyography (sEMG) of the vastus medialis (FAST = 1.3 ± 0.6%·% S P O 2 −1 ; MED = 1.1 ± 0.5%·% S P O 2 −1 ; SLOW = 0.7 ± 0.7%·% S P O 2 −1 ; P < 0.001) decreased at significantly different rates. Post hoc comparisons revealed that the rates of decline in PO and sEMG during FAST and MED were similar, and both were greater than SLOW. However, during isometric knee extension exercise, the level of force production and sEMG remained similar across saturation levels. These results confirm that decreases in absolute S P O 2 impair self-selected exercise intensity and that faster desaturation rates magnify that impairment, but only when a large muscle mass is engaged. These findings suggest that the rate of arterial deoxygenation independently influences exercise performance and that the central depressant effect may be a function of the metabolic strain associated with hypoxia, rather than the hypoxia per se.

Acute consumption of a branched chain amino acid and vitamin B-6 containing sports drink does not improve multiple sprint exercise performance, but increases post-exercise blood glucose

“…The initial workload of the test was set at 90 W and increased in a step-wise fashion by 30 W every 3 min. The test was terminated when (1) the participant was not able to maintain their cadence within 20 RPM of their self-selected target for more than 30 s; or (2) the participant reached volitional fatigue (43). During the test protocol, expired gas was collected and V Ȯ2peak was measured using an automated gas analyzer (TrueOne 2,400, ParvoMed, United States).…”