

Author: Robinson William R. Pullinger Samuel A. Kerry Jonathan W. Giacomoni Magali Robertson Colin M. Burniston Jatin G. Waterhouse James M. Edwards Ben J.
Publisher: Informa Healthcare
ISSN: 0742-0528
Source: Chronobiology International, Vol.30, Iss.8, 2013-10, pp. : 998-1010
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Abstract
Muscle force production and power output in active males, regardless of the site of measurement (hand, leg, or back), are higher in the evening than the morning. This diurnal variation is attributed to motivational, peripheral, and central factors and higher core and, possibly, muscle temperatures in the evening. This study investigated whether decreasing evening resting rectal temperatures to morning values, by immersion in a water tank, leads to muscle force production and power output becoming equal to morning values in motivated subjects. Ten healthy active males (mean ± SD: age, 22.5 ± 1.3 yrs; body mass, 80.1 ± 7.8 kg; height, 1.72 ± 0.05 m) completed the study, which was approved by the local ethics committee of the university. The subjects were familiarized with the techniques and protocol and then completed three sessions (separated by at least 48 h): control morning (07:30 h) and evening (17:30 h) sessions (with an active 5-min warm-up on a cycle ergometer at 150 W) and then a further session at 17:30 h but preceded by an immersion in cold water (∼16.5 °C) to lower rectal temperature (Trec) to morning values. During each trial, three measures of grip strength, isokinetic leg strength measurements (of knee flexion and extension at 1.05 and 4.19 rad s−1 through a 90° range of motion), and three measures of maximal voluntary contraction (MVC) on an isometric dynamometer (utilizing the twitch-interpolation technique) were performed. Trec, rating of perceived exertion (RPE), and thermal comfort (TC) were also measured after the subjects had reclined for 30 min at the start of the protocol and prior to the measures for grip, isokinetic, and isometric dynamometry. Muscle temperature was taken after the warm-up or water immersion and immediately before the isokinetic and MVC measurements. Data were analyzed using general linear models with repeated measures. Trec values were higher at rest in the evening (by 0.37 °C;
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