title: Frontal and motor cortex oxygenation during maximal exercise in normoxia and hypoxia.
abstract: Reductions in prefrontal oxygenation near maximal exertion may limit exercise performance by impairing executive functions that influence the decision to stop exercising; however, whether deoxygenation also occurs in motor regions that more directly affect central motor drive is unknown. Multichannel near-infrared spectroscopy was used to compare changes in prefrontal, premotor, and motor cortices during exhaustive exercise. Twenty-three subjects performed two sequential, incremental cycle tests (25 W/min ramp) during acute hypoxia [79 Torr inspired Po(2) (Pi(O(2)))] and normoxia (117 Torr Pi(O(2))) in an environmental chamber. Test order was balanced, and subjects were blinded to chamber pressure. In normoxia, bilateral prefrontal oxygenation was maintained during low- and moderate-intensity exercise but dropped 9.0 +/- 10.7% (mean +/- SD, P < 0.05) before exhaustion (maximal power = 305 +/- 52 W). The pattern and magnitude of deoxygenation were similar in prefrontal, premotor, and motor regions (R(2) > 0.94). In hypoxia, prefrontal oxygenation was reduced 11.1 +/- 14.3% at rest (P < 0.01) and fell another 26.5 +/- 19.5% (P < 0.01) at exhaustion (maximal power = 256 +/- 38 W, P < 0.01). Correlations between regions were high (R(2) > 0.61), but deoxygenation was greater in prefrontal than premotor and motor regions (P < 0.05). Prefrontal, premotor, and motor cortex deoxygenation during high-intensity exercise may contribute to an integrative decision to stop exercise. The accelerated rate of cortical deoxygenation in hypoxia may hasten this effect.
authors.affiliation: University of Colorado Altitude Research Center, Denver and Colorado Springs Campuses, Colorado Springs, CO 80918, USA. asubudhi@uccs.edu
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Subudhi
authors.forename: Brittany R
authors.initials: BR
authors.lastname: Miramon
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Granger
authors.forename: Robert C
authors.initials: RC
authors.lastname: Roach
mesh_terms: D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D009044:Motor Cortex / Q000502:physiology* / Q000503:physiopathology; D010101:Oxygen Consumption / Q000502:physiology*; D017397:Prefrontal Cortex / Q000502:physiology* / Q000503:physiopathology; D019265:Spectroscopy, Near-Infrared; D017585:Ultrasonography, Doppler, Transcranial
chemical_list: D002245:Carbon Dioxide