Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC209
Effects of Intense Exercise on Muscle and Cerebral Oxygenation During Acute Hypoxia
W. Duff1, B. Dahlstrom1, S. Poloskei1, M. Kohl-Bareis2, J. Neary1
1. Kinesiology and Health, University of Regina, Regina, Saskatchewan, Canada. 2. Biomedical Optics, University of Applied Science, Remagen, Germany.
A central debate in exercise science literature is the nature of fatigue (central and/or peripheral) that determines exercise performance under different conditions (3). Hypoxia has a small but direct role on the cessation of exercise, specifically during endurance performances (1, 2). Furthermore, the pacing strategy is thought to be altered when the endpoint is falsified and the external environment is known to alter physiological variables (4). In this study we examined the effects of hypoxia and pacing strategy on central (brain) and peripheral (muscle) changes in trained cyclists. Cyclists (n=10; ages = 27.3 ± 6.25yrs) performed a maximal aerobic capacity (VO2max= 52.99 ± 6.68ml/kg/min) test prior to two 20km time trials (20TT) in randomly assigned order; one in normoxia (N; 21% O2) and one in acute hypoxia (H; 15% O2). Participants were blinded to time, distance, grade of incline, and condition. Near infrared spectroscopy (NIRS) was used continuously to monitor changes in central (pre-frontal cortex) and peripheral (vastus lateralis) tissue oxygenation. Absolute NIRS data was converted to relative data and averaged (HbO2AVG, tHbAVG and HHbAVG respectively) between all participants at every 1% interval of the 20TT’s, as was WattsAVG. Rate of perceived exertions (RPE) was recorded every 4kms (subject blinded). Data was analyzed in PASW Statistics 18. There was a significant difference in time to completion (N = 51.22 ± 8.98mins, H= 57.14 ± 9.63mins) and WattsAVG (N = 237.± 10.16, H= 198.76±11.54), but not RPE at any of the 5 intervals. There were significant differences in NIRS at site of pre-frontal cortex in HbO2 (N= 11.52 ± 6.15Δμmol, H= 7.09 ± 5.10Δμmol) and tHb (N= 14.88 ± 7.27Δμmol, H= 6.75 ± 5.93Δμmol), but not HHb (N= 2.14 ± 1.44Δμmol, H= 1.92 ± 1.35Δμmol) and at site of vastus lateralis in HbO2 (N= -1.20 ± 0.48Δµmol, H= -2.81 ± 1.55Δµmol), HHb (N= 7.51 ± 0.72Δµmol, H= 8.20 ± 0.85Δµmol) and tHb (N= 6.29 ± 0.93Δµmol, H= 4.70 ± 1.47Δµmol). Decreased tHbAVG and HbO2AVG to the pre-frontal cortex requiring a greater degree of haemoglobin difference (HbDiff = HbO2 - HHb) in hypoxia indicates possible ischemia to the conscious decision making area of the brain, thus correlating with a decrease in voluntary motor output implying a greater degree of central fatigue during hypoxia. An increased time to completion in hypoxia and significantly reduced WattsAVG would support a reduction in motor unit recruitment; RPE was not altered and an ‘endspurt’ was evident in both conditions.
Where applicable, experiments conform with Society ethical requirements