Does Raising Morning Rectal Temperature to Evening Levels Offset the Diurnal Variation in Muscle Force Production?

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 in 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 increasing morning rectal temperatures to evening resting values, by active or passive warm-ups, leads to muscle force production and power output becoming equal to evening values in motivated subjects. Ten healthy active males (mean ± SD: age, 21.2 ± 1.9 yrs; body mass, 75.4 ± 8 kg; height, 1.76 ± .06 m) completed the study, which was approved by the University Ethics Committee. The subjects were familiarized with the techniques and protocol and then completed four 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) and then two further sessions at 07:30 h but proceeded by an extended active or passive warm-up to raise rectal temperature to evening values. These last two sessions were counterbalanced in order of administration. During each trial, three measures of handgrip 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 four measures of maximal voluntary contraction (MVC) on an isometric ergometer (utilizing the twitch-interpolation technique) were performed. Rectal and intra-aural temperatures, ratings of perceived exertion (RPE) and thermal comfort (TC) were measured. Measurements were made after the subjects had reclined for 30 min and after the warm-ups and prior to the measurement of handgrip and isokinetic and isometric ergometry. Muscle temperature was taken after the warm-up and immediately before the isokinetic and MVC measurements. Warm-ups were either active (cycle ergometer at 150 W) or passive (resting in a room at 35 °C, relative humidity 45%). Data were analyzed using analysis of variance models with repeated measures. Rectal and intra-aural temperatures were higher at rest in the evening (.56 °C and .74 °C; p < .05) than in the morning, but there were no differences after the active or passive warm-ups, the subjects' ratings of thermal comfort reflecting this. Muscle temperatures also displayed significant diurnal variation, with higher values in the evening (~.31 °C; p < .05). Grip strength, isokinetic knee flexion for peak torque and peak power at 1.05 rad.s(-1), and knee extension for peak torque at 4.19 rad.s(-1) all showed higher values in the evening. All other measures of strength or power showed a trend to be higher in the evening ( .10 > p > .05). There was no significant effect of active or passive warm-ups on any strength or power variable, and subjects reported maximal values for effort for each strength measure. In summary, effects of time of day were seen in some measures of muscle performance but, in this population of motivated subjects, there was no evidence that increasi...

Does Lowering Evening Rectal Temperature to Morning Levels Offset the Diurnal Variation in Muscle Force Production?

“…These changes were observed in highly motivated individuals (effort scores of $98%; Drust et al, 2005;Edwards et al, 2013;Giacomoni et al, 2005). This result applied to a range of measurements that have been shown by us previously and in the literature to exhibit diurnal variation (grip strength, isokinetic, and isometric dynamometry with percutaneous stimulation that removes central factors from the amount of muscle force produced; a range of 3-14%).…”

“…The alpha level of significance was set at 5% (p50.05). In order to reduce interindividual differences, all of an individual's rectal and muscle temperatures and muscle performance data were normalized and then expressed as a percentage of the evening values (as done previously; Edwards et al, 2013). When the SPSS output demonstrated a significance level of p ¼ 0.000, these were corrected to p50.0005 (Kinear & Gray, 1995).…”

“…It is proposed that the higher evening core body temperature ($0.8 C in rectal and gut sites; Edwards et al, 2002) and local muscle temperature ($0.31 C in vastus lateralis; Edwards et al, 2013) produce an increase in force-generating capacity of the muscle (Bernard et al, 1998;Coldwells et al, 1994;Giacomoni et al, 2005;Melhim, 1993) and neural function (reduced twitch time course or increase in speed of contraction; Martin et al, 1999).…”

“…The first, which has received some interest in the literature, involves using either passive (raising core temperature by some external means) or active (utilizing exercise) ''warm-ups'' to increase core body temperature in the morning to approximately, or precisely, the temperatures found ''at rest'' in the evening; and investigating if this increases morning performance to evening values (either cycling or swimming time-trial completion or muscle force production; see Edwards et al, 2013, for further details). The second link, which has received far less attention so far, investigates if pre-cooling rectal temperature in the evening to values observed in the morning results in a concurrent decrease in muscle performance to morning values.…”

Human circadian rhythms and exercise: Significance and application in real-life situations

“…Recently, interesting reports have evaluated muscle strength in the morning and evening with body temperature manipulation. In one study 33) , the effect of active or passive warm-up on muscle strength was examined. Active warm-up included bicycle exercise, and passive warm-up was resting in a room at 35°C, 45% RH (relative humidity).…”