6 studies about performance in heat

With only 3 weeks to Petra Desert Marathon, my concern is to find a practical method to cool my body temperature either before with a long term effect or during the race.
A few studies I found, but can be difficult to used it practically.

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Stevens CJ1, Bennett KJ, Sculley DV, Callister R, Taylor L, Dascombe BJ., A COMPARISON OF MIXED-METHOD COOLING INTERVENTIONS ON PRELOADED RUNNING PERFORMANCE IN THE HEAT, J Strength Cond Res. 2017 Mar;31(3):620-629. 

This study compared mixed-method cooling interventions on preloaded running performance in the heat. N11 trained male runners completed randomized, preloaded running time trials (20 minutes at 70%VO2max and a 3 km time trial) on a nonmotorized treadmill in the heat (33° C). Trials consisted of precooling by combined cold-water immersion and ice slurry ingestion (PRE), midcooling by combined facial water spray and menthol mouth rinse (MID), a combination of all methods (ALL), and control (CON).

Performance time was significantly faster in MID (13.7 ± 1.2 minutes; p < 0.01) and ALL (13.7 ± 1.4 minutes; p = 0.04) but not PRE (13.9 ± 1.4 minutes; p = 0.24) when compared with CON (14.2 ± 1.2 minutes). Precooling significantly reduced rectal temperature (initially by 0.5 ± 0.2° C), mean skin temperature, heart rate and sweat rate, and increased iEMG activity, whereas midcooling significantly increased expired air volume and respiratory exchange ratio compared with control. Significant decreases in forehead temperature, thermal sensation, and postexercise blood prolactin concentration were observed in all conditions compared with control. Performance was improved with midcooling, whereas precooling had little or no influence. Midcooling may have improved performance through an attenuated inhibitory psychophysiological and endocrine response to the heat.

The study demonstrated that in hot conditions, such athletes should prioritize the use of cooling strategies during the event, rather than before the event when possible. A combination of different cooling methods should be implemented, including both internal and external methods. The current study demonstrated that spraying temperate water on the face and rinsing the mouth with a menthol (cold stimulus) solution were two viable options for athletes. Implementing such strategies may take the form of a small bottle of water or menthol solution (250 ml) carried on a hydration belt or using the liquid available at aid stations during the event. The goal of such cooling should be to maximize the effect on thermal sensation (making the athlete feel cooler), perhaps by targeting areas on the head and face continuously or repeatedly.

Christopher J. Stevens, Aden Kittel, Dean V. Sculley, Robin Callister, Lee Taylor & Ben J. Dascombe (2016): Running performance in the heat is improved by similar magnitude with pre-exercise cold-water immersion and mid-exercise facial water spray, Journal of Sports Sciences, DOI: 10.1080/02640414.2016.1192294

compared the effects of external pre-cooling and mid-exercise cooling methods on running time trial performance and associated physiological responses. Nine trained male runners completed familiarisation and three randomised 5 km running time trials on a non-motorised treadmill in the heat (33°C). The trials included pre-cooling by cold-water immersion (CWI), mid-exercise cooling by intermittent facial water spray (SPRAY), and a control of no cooling (CON). Temperature, cardiorespiratory, muscular activation, and perceptual responses were measured as well as blood concentrations of lactate and prolactin.

In summary, self-paced running performance in the heat was improved by a similar magnitude (~3%) with either pre-cooling by CWI or mid-cooling by intermittent facial water spray when compared to no cooling intervention. Both strategies are likely ergogenic for endurance running performance in the heat. CWI significantly reduced rectal temperature and sweat rate, but no changes in heart rate were observed, and hence it is unclear if cooling induced cardiovascular adjustments. It is proposed that reduced perceptions of heat discomfort following the cooling interventions facilitated an increase in self selected work output to match an anticipated psychophysiological strain at the end of exercise.

Stevens CJ1, Taylor L2, Dascombe B, Cooling During Exercise: An Overlooked Strategy for Enhancing Endurance Performance in the Heat. Sports Med. 2017 May;47(5):829-841. doi: 10.1007/s40279-016-0625-7.

Key points

  • Mid-cooling (cooling during exercise) through the ingestion of cold fluids or ice slurry (with or without a menthol additive), as well as cooling the neck and face region via a cooling collar or water spray is beneficial for endurance performance in the heat.
  • Mechanisms of performance enhancement with midcooling likely include reductions in cardiovascular strain, lower skin temperature, enhanced central nervous system function and improved perception of thermal sensation, comfort and exertion.
  • Future research should compare the effects of different cooling strategies (both separately and together) in highly trained athletes, with a focus on practical methods (for example, lightweight active cooling clothing and headwear), within externally valid endurance time trial protocols.

C. J. Stevens , B. Thoseby , D. V. Sculley , R. Callister, L. Taylor , B. J. Dascombe, Running performance and thermal sensation in the heat are improved with menthol mouth rinse but not ice slurry ingestion, Scand J Med Sci Sports 2015:doi: 10.1111/sms.12555

Compare the effects of a cooling strategy designed to predominately lower thermal state with a strategy designed to lower thermal sensation on endurance running performance and physiology in the heat. N11 moderately trained male runners completed familiarization and three randomized, crossover 5-km running time trials on a non-motorized treadmill in hot conditions (33 °C).

The trials included ice slurry ingestion before exercise (ICE), menthol mouth rinse during exercise (MEN), and no intervention (CON).

The data demonstrate that a change in the perception of thermal sensation during exercise from menthol mouth rinse was associated with improved endurance running performance in the heat. Ice slurry ingestion reduced core temperature but did not decrease thermal sensation during exercise or improve running performance.

Mejuto G1, Chalmers S2, Gilbert S3, Bentley D4.  The effect of ice slurry ingestion on body temperature and cycling performance in competitive athletes. J Therm Biol. 2018 Feb;72:143-147. doi: 10.1016/j.jtherbio.2018.01.012. Epub 2018 Feb 2.

7 cyclists underwent three trials comprising of 45 min steady state cycling (SS) at 70% VO2 max and a subsequent 10 km time trial (TT) in hot conditions (32 °C, 50% relative humidity).

The intervention consisted of: (1) ingestion of thermo-neutral beverage before and during SS cycling (TN), (2) ingestion of ice slurry beverage and application of iced towels (precooling) prior to exercise, and then ingestion of thermo-neutral beverage during SS (PRE) and (3) precooling strategy as above plus ice slurry ingestion during SS cycling (PRE + MID). Accordingly, both precooling and a combination of precooling and mid-cooling during exercise in hot conditions may be a practical and effective way of reducing core temperature. Future studies should investigate longer distance events and timing of ice slurry ingestion.

Jones PR1, Barton C, Morrissey D, Maffulli N, Hemmings S., Pre-cooling for endurance exercise performance in the heat: a systematic review, BMC Med. 2012 Dec 18;10:166. doi: 10.1186/1741-7015-10-166.

This systematic literature review (2012) synthesizes the current findings of the effects of pre-cooling on endurance exercise performance, providing guidance for clinical practice and further research.

Current evidence indicates cold water immersion may be the most effective method of pre-cooling to improve endurance performance in hot conditions, although practicality must be considered. Ice slurry ingestion appears to be the most promising practical alternative. Interestingly, cooling garments appear of limited efficacy, despite their frequent use. Mechanisms behind effective pre-cooling remain uncertain, and optimal protocols have yet to be established. Future research should focus on standardizing exercise performance protocols, recruiting larger participant numbers to enable direct comparisons of effectiveness and practicality for each method, and ensuring potential adverse events are evaluated

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