title: Determinants of skin sympathetic nerve responses to isometric exercise.
abstract: Exercise-induced increases in skin sympathetic nerve activity (SSNA) are similar between isometric handgrip (IHG) and leg extension (IKE) performed at 30% of maximal voluntary contraction (MVC). However, the precise effect of exercise intensity and level of fatigue on this relationship is unclear. This study tested the following hypotheses: 1) exercise intensity and fatigue level would not affect the magnitude of exercise-induced increase in SSNA between IHG and IKE, and 2) altering IHG muscle mass would also not affect the magnitude of exercise-induced increase in SSNA. In protocol 1, SSNA (peroneal microneurography) was measured during baseline and during the initial and last 30 s of isometric exercise to volitional fatigue in 12 subjects who randomly performed IHG and IKE bouts at 15, 30, and 45% MVC. In protocol 2, SSNA was measured in eight subjects who performed one-arm IHG at 30% MVC with the addition of IHG of the contralateral arm in 10-s intervals for 1 min. Exercise intensity significantly increased SSNA responses during the first 30 s of IHG (34+/-13, 70+/-11, and 92+/-13% change from baseline) and IKE (30+/-17, 69+/-12, and 76+/-13% change from baseline) for 15, 30, and 45% MVC. During the last 30 s of exercise to volitional fatigue, there were no significant differences in SSNA between exercise intensities or limb. SSNA did not significantly change between one-arm and two-arm IHG. Combined, these data indicate that exercise-induced increases in SSNA are intensity dependent in the initial portion of isometric exercise, but these differences are eliminated with the development of fatigue. Moreover, the magnitude of exercise-induced increase in SSNA responses is not dependent on either muscle mass involved or exercising limb.
authors.affiliation: Dept. of Medicine, Pennsylvania State Univ. College of Medicine, Hershey, PA, USA. thad.e.wilson@drexel.edu
authors.forename: Thad E
authors.initials: TE
authors.lastname: Wilson
authors.forename: Damian J
authors.initials: DJ
authors.lastname: Dyckman
authors.forename: Chester A
authors.initials: CA
authors.lastname: Ray
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005260:Female; D005542:Forearm / Q000502:physiology; D018737:Hand Strength / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007866:Leg / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D012039:Regional Blood Flow; D012867:Skin / Q000098:blood supply / Q000294:innervation*; D016683:Supine Position; D013564:Sympathetic Nervous System / Q000502:physiology*; D013997:Time Factors