title: Muscle cooling delays activation of the muscle metaboreflex in humans.
abstract: Elevation of muscle temperature has been shown to increase muscle sympathetic nerve activity (MSNA) during isometric exercise in humans. The purpose of the present study was to evaluate the effect of muscle cooling on MSNA responses during exercise. Eight subjects performed ischemic isometric handgrip at 30% of maximal voluntary contraction to fatigue followed by 2 min of postexercise muscle ischemia (PEMI), with and without local cooling of the forearm. Local cooling of the forearm decreased forearm muscle temperature from 31.8 +/- 0.4 to 23.1 +/- 0.8 degrees C (P = 0.001). Time to fatigue was not different during the control and cold trials (156 +/- 11 and 154 +/- 5 s, respectively). Arterial pressures and heart rate were not significantly affected by muscle cooling during exercise, although heart rate tended to be higher during the second minute of exercise (P = 0.053) during muscle cooling. Exercise-induced increases in MSNA were delayed during handgrip with local cooling compared with control. However, MSNA responses at fatigue and PEMI were not different between the two conditions. These findings suggest that muscle cooling delayed the activation of the muscle metaboreflex during ischemic isometric exercise but did not prevent its full expression during fatiguing contraction. These results support the concept that muscle temperature can play a role in the regulation of MSNA during exercise.
authors.affiliation: Department of Exercise Science, University of Georgia, Athens 30602, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Ray
authors.forename: K M
authors.initials: KM
authors.lastname: Hume
authors.forename: K H
authors.initials: KH
authors.lastname: Gracey
authors.forename: E T
authors.initials: ET
authors.lastname: Mahoney
mesh_terms: D000328:Adult; D001794:Blood Pressure; D001831:Body Temperature; D003080:Cold Temperature; D005260:Female; D018737:Hand Strength; D006339:Heart Rate; D006801:Humans; D007511:Ischemia; D008297:Male; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000098:blood supply / Q000294:innervation / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D012881:Skin Temperature; D013564:Sympathetic Nervous System / Q000502:physiology