title: Effect of muscle temperature on rate of oxygen uptake during exercise in humans at different contraction frequencies.
abstract: The effect of elevated human muscle temperature on energy turnover was investigated during cycling exercise (at 85 % of (VO(2)max)) at a contraction frequency of 60 revs min(-1). Muscle temperature was passively elevated prior to exercise by immersion of the legs in a hot water bath (42 degrees C). During exercise at this low pedalling rate, total energy turnover was higher (P<0.05) when muscle temperature was elevated compared with normal temperature (70.4+/-3.7 versus 66.9+/-2.4 kJ min(-1), respectively). Estimated net mechanical efficiency was found to be lower when muscle temperature was elevated. A second experiment was conducted in which the effect of elevated human muscle temperature on energy turnover was investigated during cycling exercise (at 85 % of (VO(2)max)) at a contraction frequency of 120 revs min(-1). Under the conditions of a high pedalling frequency, an elevated muscle temperature resulted in a lower energy turnover (P<0.05) compared with the normal muscle temperature (64.9+/-3.7 versus 69.0+/-4.7 kJ min(-1), respectively). The estimated net mechanical efficiency was therefore higher when muscle temperature was elevated. We propose that, in these experiments, prior heating results in an inappropriately fast rate of cross-bridge cycling when exercising at 60 revs min(-1), leading to an increased energy turnover and decreased efficiency. However, at the faster pedalling rate, the effect of heating the muscle shifts the efficiency/velocity relationship to the right so that cross-bridge detachment is more appropriately matched to the contraction velocity and, hence, energy turnover is reduced.
authors.affiliation: Centre for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Hassall Road, Alsage, Alsager ST7 2HL, UK. richard.ferguson@strath.ac.uk
authors.forename: Richard A
authors.initials: RA
authors.lastname: Ferguson
authors.forename: Derek
authors.initials: D
authors.lastname: Ball
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Sargeant
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology; D001696:Biomechanical Phenomena; D001831:Body Temperature; D002245:Carbon Dioxide / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D019344:Lactic Acid / Q000097:blood / Q000378:metabolism; D008297:Male; D009043:Motor Activity / Q000502:physiology; D018482:Muscle, Skeletal / Q000098:blood supply / Q000378:metabolism* / Q000502:physiology; D010100:Oxygen / Q000493:pharmacokinetics*
chemical_list: D002245:Carbon Dioxide; D019344:Lactic Acid; D010100:Oxygen