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

Abstract

The present study investigated whether increasing morning rectal temperatures (T) to evening levels, or increasing morning and evening T to an "optimal" level (38.5°C), resulting in increased muscle temperatures (T), would offset diurnal variation in repeated sprint (RS) performance in a causal manner. Twelve trained males underwent five sessions [age (mean ± SD) 21.0 ± 2.3 years, maximal oxygen consumption (V̇Omax) 60.0 ± 4.4 mL.kg min, height 1.79 ± 0.06 m, body mass 78.2 ± 11.8 kg]. These included control morning (M, 07:30 h) and evening (E, 17:30 h) sessions (5-min warm-up), and three further sessions consisting of a warm-up morning trial (M, in 39-40°C water) until T reached evening levels; two "optimal" trials in the morning and evening (M and E, in 39-40°C water) respectively, until T reached 38.5°C. All sessions included 3 × 3-s task-specific warm-up sprints, thereafter 10 × 3-s RS with 30-s recoveries were performed a non-motorised treadmill. T and T measurements were taken at the start of the protocol and following the warm-up periods. Values for T and T at rest were higher in the evening compared to morning values (0.48°C and 0.69°C, p < 0.0005). RS performance was lower (7.8-8.3%) in the M for distance covered (DC; p = 0.002), average power (AP; p = 0.029) and average velocity (AV; p = 0.002). Increasing T in the morning to evening values or optimal values (38.5°C) did not increase RS performance to evening levels (p = 1.000). However, increasing T in the evening to "optimal" level through a passive warm-up significantly reduced DC (p = 0.008), AP (p < 0.0005) and AV (p = 0.007) to values found in the M condition (6.0-6.9%). Diurnal variation in T and T is not wholly accountable for time-of-day oscillations in RS performance on a non-motorised treadmill; the exact mechanism(s) for a causal link between central temperature and human performance are still unclear and require more research.

Effects of an active warm-up on variation in bench press and back squat (upper and lower body measures)

“…In the current study left and right isometric grip strength followed the previously reported daily fluctuation with highest values in the evening than the morning and a variation of 4.6 % and 6.5 % of the 24-h mean, -similar to 6 % values reported by Reilly et al (2007). Furthermore, a diurnal variation in resting Trec values of 0.53°C was found, similar to values previously reported (Edwards et al 2013;Pullinger et al 2014Pullinger et al , 2018aPullinger et al , 2018bRobertson et al 2018). Our findings agree with current literature regarding time-of-day variation in Trec and muscle force output (Edwards et al 2013).…”

“…To the best of our knowledge, this is only the second study to demonstrate diurnal variation in bench press and back squat, but the first to assess the effect of an active warm-up on multi-joint exercises. Relatively few studies have looked at precise modelling of pre-exercise temperature (by removing individuals from the active warming stimulus when the required Trec was reached) through an active warm-up (Edwards et al 2013;Pullinger et al 2018a). It has previously been established that the use of an active warm-up of standard duration (Sim et al 2009;Taylor et al 2013;Yaicharoen et al 2012), results in producing large variations in core and/or Tm within individuals.…”

“…At present, the exact mechanisms underpinning diurnal variation in human performance are still unknown but have been attributed to several factors (Edwards et al 2013;Pullinger et al 2018aPullinger et al , 2018b. It is believed that peripheral or muscle-related variables (contractibility, metabolism and morphology of muscle fibres and local muscle temperature), which are in turn influenced by hormonal and ionic muscle process variations (Reilly and Waterhouse, 2009;Tamm et al 2009), and/or central/neurological factors (central nervous system command; alertness; motivation and mood: Castaingts et al 2004;Giacomoni et al 2005;Racinais et al 2005;2010) affect diurnal variation in muscle performance.…”

“…It has been proposed that the higher evening resting core 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;Pullinger et al 2018a,b) produce an increase in force-generating capacity of the muscle (Bernard et al 1998;Giacomoni et al 2005) and neural function such that there is a reduced twitch time-course or increase in speed of contraction (Martin et al 1999). In order to determine whether or not core temperature and/or muscle temperature (Tm) plays a role in performance, manipulation of morning or evening temperatureseither by increasing morning temperatures to evening levels or decreasing evening temperatures to morning values has previously been studied assessing muscle force, power output and repeated sprint (RS) performance as performance outcomes (Edwards et al 2013;Pullinger et al 2018aPullinger et al , 2018b.…”

“…The use of an active (by means of exercise) "warm-up" to increase rectal temperature (Trec) in the morning, to approximately, or precisely, the temperature previously found at rest in the evening, and then examining whether this increases morning performance to evening levels could help establish whether or not manipulation of central temperature, which at rest has a high endogenous component, may provide some exogenous effect to the observed diurnal variation in bench press and back squat. Numerous studies have shown improvements in muscular performance (O'Brien et al 1997;Sargeant, 1987;Souissi et al 2010;Stewart & Sleivert, 1998) to take place following an active warm-up while others have reported no significant effects or a decrease in performance (Mitchell & Huston 1993;Pullinger et al 2018a;Pyke, 1968;Sargeant, 1987;Stewart & Sleivert 1998). Further, research has found that the duration and type of warmup affects short-term muscular performance (Souissi et al 2010;Baklouti et al 2015).…”