title: Effect of arterial oxygenation on quadriceps fatigability during isolated muscle exercise.
abstract: The effect of various levels of oxygenation on quadriceps muscle fatigability during isolated muscle exercise was assessed in six male subjects. Twitch force (Q(tw)) was assessed using supramaximal magnetic femoral nerve stimulation. In experiment 1, maximal voluntary contraction (MVC) and Q(tw) of resting quadriceps muscle were measured in normoxia [inspired O(2) fraction (Fi(O(2))) = 0.21, percent arterial O(2) saturation (Sp(O(2))) = 98.4%, estimated arterial O(2) content (Ca(O(2))) = 20.8 ml/dl], acute hypoxia (Fi(O(2)) = 0.11, Sp(O(2)) = 74.6%, Ca(O(2)) = 15.7 ml/dl), and acute hyperoxia (Fi(O(2)) = 1.0, Sp(O(2)) = 100%, Ca(O(2)) = 22.6 ml/dl). No significant differences were found for MVC and Q(tw) among the three Fi(O(2)) levels. In experiment 2, the subjects performed three sets of nine, intermittent, isometric, unilateral, submaximal quadriceps contractions (62% MVC followed by 1 MVC in each set) while breathing each Fi(O(2)). Q(tw) was assessed before and after exercise, and myoelectrical activity of the vastus lateralis was obtained during exercise. The percent reduction of twitch force (potentiated Q(tw)) in hypoxia (-27.0%) was significantly (P < 0.05) greater than in normoxia (-21.4%) and hyperoxia (-19.9%), as were the changes in intratwitch measures of contractile properties. The increase in integrated electromyogram over the course of the nine contractions in hypoxia (15.4%) was higher (P < 0.05) than in normoxia (7.2%) or hyperoxia (6.7%). These results demonstrate that quadriceps muscle fatigability during isolated muscle exercise is exacerbated in acute hypoxia, and these effects are independent of the relative exercise intensity.
authors.affiliation: The John Rankin Laboratory of Pulmonary Medicine, Department of Health, University of Wisconsin-Madison, 4245 Medical Science Center, 1300 University Ave., Madison, WI 53706, USA. katayama@htc.nagoya-u.ac.jp
authors.forename: Keisho
authors.initials: K
authors.lastname: Katayama
authors.forename: Markus
authors.initials: M
authors.lastname: Amann
authors.forename: David F
authors.initials: DF
authors.lastname: Pegelow
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Jacques
authors.forename: Jerome A
authors.initials: JA
authors.lastname: Dempsey
mesh_terms: D000328:Adult; D001642:Bicycling; D015444:Exercise / Q000502:physiology*; D005267:Femoral Nerve / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology; D007537:Isometric Contraction; D008280:Magnetics; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D010100:Oxygen / Q000097:blood* / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D052097:Quadriceps Muscle / Q000294:innervation / Q000502:physiology*; D013997:Time Factors
chemical_list: D010100:Oxygen