Does Lowering Evening Rectal Temperature to Morning 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 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; p < 0.05) than the morning, but values were no different from morning values immediately after the passive pre-cooling. However, Trec progressively decreased throughout the experiments, this being reflected in the subjects' ratings of thermal comfort. Muscle temperatures also displayed significant diurnal variation, with higher values in the evening (by 0.39 °C; p < 0.05). Right grip strength, isometric peak power, isokinetic knee flexion and extension 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 (a range of 3-14%), and all other measures of strength or power showed a statistical trend to be higher in the evening (0.10 > p > 0.05). Pre-cooling in the evening significantly reduced force or power variables towards morning values. In summary, effects of time of day were seen in some measures of muscle performance, in agreement with past research. However, in this population of motivated subjects, there was evidence that decreasing evening Trec to morning values by coldwater immersion decreased muscle st...

Is there a diurnal variation in repeated sprint ability on a non-motorised treadmill?

“…These are in agreement with previous research conducted by Edwards et al (2013), who found morning and evening differences ranging from $0.50 C to $0.30 C for T rec and T m , respectively. Another recent study performed (Robinson et al, 2013) also demonstrated similar diurnal differences in T rec and T m , both by about $0.40 C. The evening superiority in muscle force production and power output has been attributed to a causal link between ''resting'' core and muscle temperatures and performance, the higher evening temperatures producing an increase in the 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).…”

Diurnal variation in repeated sprint performance cannot be offset when rectal and muscle temperatures are at optimal levels (38.5°C)

“…The exact mechanisms for this observed diurnal variation in human performance are still unknown but have been attributed to a number of factors (See Edwards et al, 2013 andPullinger et al, 2013;2014). One factor which has been proposed is the causal link of the temperature rhythm, which might be implicated directly or indirectly, where the higher evening resting core body temperature (~0.8°C in rectal and gut sites, Edwards et al, 2002) and local muscle temperature (≥ ~0.35°C in vastus lateralis at depths of 3 cm, Edwards et al, 2013;Robinson et al, 2013;Pullinger et al, 2013;2017) 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 link between core temperature and performance has been studied predominantly using either active (by means of exercise) or passive (by means of a chamber or water bath) "warm-ups" to increase rectal body temperature in the morning, to approximately, or precisely, the temperature found in the evening;…”

“…However, passive exposure to hot environments (either a 30-min exposure to a hot bath at 38°C, with legs from feet to pelvis immersed or 1 h at 29.5°C, 74 ±10% relative humidity ambient air) blunts muscle force diurnal variation in performance (a squat jump [SJ], a counter-movement jump [CMJ], and a brief maximal sprint on cycle ergometer; Racinais et al, 2004;. Interpretation of some of these results are compromised by the complexity of the protocols), with core and muscle temperature cooling evident as the protocol progressedwith focus on only one key measure suggested (Edwards et al, 2013;Robinson et al, 2013). Interestingly, when combining both internal (i.e., afternoon central temperature) and external passive warm-up in the afternoon, evidence points towards a 'ceiling' effect, whereby muscular force cannot be increased further (Racinais et al 2005a(Racinais et al , 2005b(Racinais et al , 2009.…”

The circadian clock and human athletic performance

“…The heterogeneity in some studies and daily variations in the strength, power and force of skeletal muscle attributes to the peripheral clocks that possess temperature-dependent and temperature-independent mechanisms (Robinson et al, 2013). Many authors emphasize that although the temperature is the chief marker of sports performance, some variables such as the state of vigilance and alertness, and mood levels (which are the highest in the morning) can affect athletic performance (Atkinson & Speirs, 1998;Reilly et al, 2003).…”