The Impact of an Ice Slurry-Induced Gastrointestinal Heat Sink on Gastrointestinal and Rectal Temperatures Following Exercise

Ad libitum ice slurry ingestion and half-marathon performance in a hot environment: A study comparing the effects of the amount and moment of ingestion between ice slurry and water at 37 °C

Ice slurry ingestion during prolonged exercises may improve performance in hot environments; however, the ideal amount and timing of ingestion are still uncertain. We determined whether ad libitum ice slurry ingestion influences physiological and perceptual variables and half-marathon performance while comparing the effects of the amount and moment of ingestion between ice slurry and water at 37 °C. Ten trained participants (28 ± 2 years; mean and SD) were required to run two half marathons while consuming either ice slurry (-1 °C; Ad-1) or water (37 °C; 37 CE) ad libitum. They then performed two other half marathons where, during one, they were required to ingest an amount of water equivalent to the amount consumed during the Ad-1 trial (Pro37), and in the other, to ingest ice slurry in the amount consumed during the 37 CE trial (Pro-1). During the half marathons, dry-bulb temperature and relative humidity were controlled at 33.1 ± 0.3 °C and 60 ± 3%, respectively. Ad-1 ingestion (349.6 ± 58.5 g) was 45% less than 37 CE ingestion (635.5 ± 135.8 g). Physical performance, heart rate, perceived exertion, body temperatures, and thermal perception were not influenced by the temperature or amount of beverage ingestion. However, a secondary analysis suggested that lower beverage ingestion was associated with improved performance (Ad-1 + Pro37 vs. 37 CE + Pro-1: -4.0 min, Cohen's d = 0.39), with a significant relationship between lower beverage ingestion and faster running time (b = 0.02, t = 4.01, p < 0.001). In conclusion, ice slurry ingestion does not affect performance or physiological or perceptual variables during a half marathon in a hot environment. Preliminary evidence suggests that lower beverage ingestion (ice slurry or warm water) is associated with improved performance compared to higher ingestion.

Rectal and gastrointestinal temperature differ during passive heating and subsequent recovery

We aimed to compare rectal temperature (Trec) and gastro-intestinal temperature (TGI) during passive heating and subsequent recovery with and without ice slurry ingestion. Twelve males (age: 25 ± 4 years, body mass index: 25.7 ± 2.5 kg m-2) were immersed in hot water on two occasions (Trec elevation: 1.82 ± 0.08°C). In the subsequent 60-min recovery in ambient conditions, participants ingested either 6.8 g kg-1 of ice slurry (-0.6°C, ICE) or control drink (37°C, CON). During passive heating, Trec was lower than TGI (P < 0.001), in the recovery, Trec was higher than TGI (P < 0.001). During passive heating, mean bias and 95%LoA (Limits of Agreement) were -0.10(±0.25)°C and -0.12(±0.36)°C for CON and ICE, respectively. In the recovery, mean bias and 95%LoA were 0.30(±0.60)°C and 0.42(±0.63)°C for CON and ICE, respectively. Trec and TGI differed during both heating and recovery, and less favourable agreement between Trec and TGI was found in the recovery from passive heating with or without ice slurry ingestion.

Effect of electric fan use in isolation or combined with ice slurry/cold water ingestion and lower-leg immersion in young men during intermittent physical activity in hot-humid conditions

Using a randomized crossover protocol, 10 young men completed four 180 min exposures (38 °C, 60% relative humidity), alternating between 30 min of walking and 30 min of sitting where fluid or ice slurry were served. Participants underwent four trials: (i) 5 mL·kg body mass-1 of 20 °C water (CON); (ii) 5 mL·kg body mass-1 of 20 °C water + fan at 4 m·s-1 (FAN); (iii) fan + 3 mL·kg body mass-1 of ice slurry + 2 mL·kg body mass-1 of 4 °C water (FAN + ISCW); and (iv) FAN + ISCW + lower-leg immersion in 20 °C water (FAN + ISCW + LLI). Sweat and body mass losses were higher with FAN than CON, FAN + ISCW, and FAN + ISCW + LLI. Mean and peak changes in Δrectal temperature, heart rate, and perceived heat and thirst from baseline were not statistically and practically different between FAN and CON. FAN + ISCW + LLI decreased sweat loss compared with FAN + ISCW and mean and peak changes in Δrectal temperature, heart rate, and perceived thirst compared with CON. FAN + ISCW + LLI also attenuated the changes in Δrectal temperature (peak) and thirst (mean and peak) compared with FAN. In conclusion, FAN slightly exacerbates fluid loss but does not attenuate the changes in Δrectal temperature, heart rate, and perceived heat and thirst during intermittent physical activity in hot-humid conditions. However, coupling ISCW or ISCW + LLI with the use of a fan attenuates the increase in these outcomes compared with no intervention and to a greater extent for rectal temperature and thirst when fan is coupled with ISCW + LLI than when it is used in isolation.

Effect of Glycerol-Induced Hyperhydration on a 5-kilometer Running Time-Trial Performance in the Heat in Recreationally Active Individuals

Maximal oxygen consumption (V˙O_2max) is a major determinant of 5-km running time-trial (TT) performance. Glycerol-induced hyperhydration (GIH) could improve V˙O_2max in recreationally active persons through an optimal increase in plasma volume. Moreover, ingestion of a large bolus of cold fluid before exercise could decrease thermal stress during exercise, potentially contributing to improved performance. We determined the effect of GIH on 5-km running TT performance in 10 recreationally active individuals (age: 24 ± 4 years; V˙O_2max: 48 ± 3 mL/kg/min). Using a randomized and counterbalanced protocol, participants underwent two, 120-min hydration protocols where they ingested a 1) 30 mL/kg fat-free mass (FFM) of cold water (~4 °C) with an artificial sweetener + 1.4 g glycerol/kg FFM over the first 60 min (GIH) or 2) 7.5 mL/kg FFM of cold water with an artificial sweetener over the first 20 min (EUH). Following GIH and EUH, participants underwent a 5-km running TT at 30 °C and 50% relative humidity. After 120 min, GIH was associated with significantly greater fluid retention (846 ± 415 mL) and plasma volume changes (10.1 ± 8.4%) than EUH, but gastrointestinal (GI) temperature did not differ. During exercise, 5-km running TT performance (GIH: 22.95 ± 2.62; EUH: 22.52 ± 2.74 min), as well as heart rate, GI temperature and perceived exertion did not significantly differ between conditions. This study demonstrates that the additional body water and plasma volume gains provided by GIH do not improve 5-km running TT performance in the heat in recreationally active individuals.

Performance effects of internal pre- and per-cooling across different exercise and environmental conditions: A systematic review

Exercise in a hot and humid environment may endanger athlete's health and affect physical performance. This systematic review aimed to examine whether internal administration of ice, cold beverages or menthol solutions may be beneficial for physical performance when exercising in different environmental conditions and sports backgrounds. A systematic search was performed in PubMed, Web of Science, Scopus and SPORTDiscus databases, from inception to April 2022, to identify studies meeting the following inclusion criteria: healthy male and female physically active individuals or athletes (aged ≥18 years); an intervention consisting in the internal administration (i.e., ingestion or mouth rinse) of ice slush, ice slurry or crushed ice and/or cold beverages and/or menthol solutions before and/or during exercise; a randomized crossover design with a control or placebo condition; the report of at least one physical performance outcome; and to be written in English. Our search retrieved 2,714 articles in total; after selection, 43 studies were considered, including 472 participants, 408 men and 64 women, aged 18-42 years, with a VO2max ranging from 46.2 to 67.2 mL⋅kg-1⋅min-1. Average ambient temperature and relative humidity during the exercise tasks were 32.4 ± 3.5°C (ranging from 22°C to 38°C) and 50.8 ± 13.4% (varying from 20.0% to 80.0%), respectively. Across the 43 studies, 7 exclusively included a menthol solution mouth rinse, 30 exclusively involved ice slurry/ice slush/crushed ice/cold beverages intake, and 6 examined both the effect of thermal and non-thermal internal techniques in the same protocol. Rinsing a menthol solution (0.01%) improved physical performance during continuous endurance exercise in the heat. Conversely, the ingestion of ice or cold beverages did not seem to consistently increase performance, being more likely to improve performance in continuous endurance trials, especially when consumed during exercises. Co-administration of menthol with or within ice beverages seems to exert a synergistic effect by improving physical performance. Even in environmental conditions that are not extreme, internal cooling strategies may have an ergogenic effect. Further studies exploring both intermittent and outdoor exercise protocols, involving elite male and female athletes and performed under not extreme environmental conditions are warranted. Systematic review registration: [https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021268197], identifier [CRD42021268197].

Differences between sexes in thermoregulatory responses and exercise time during endurance exercise in a hot environment following pre-cooling with ice slurry ingestion

This study aimed to examine differences between sexes in thermoregulatory responses and exercise time after ice slurry ingestion in a hot environment. Twenty-four healthy adults (male n = 12, body weight (BW) = 65.8 ± 10.3; female n = 12, BW = 58.2 ± 10.0) ingested 7.5 g/kg of either ice slurry at -1 °C (ICE) or control water at 20 °C (CON) before cycling at 55%VO₂ max in a hot environment (controlled at 38 °C, 40% relative humidity). Rectal (Tre) and skin (Tsk) temperature, heart rate, sweat rate, respiratory gases, ratings of thermal sensation (TS), thermal comfort (TC), and rating of perceived exertion (RPE) were measured. Ice slurry did not improve exercise time in both sexes despite Tre was significantly lower in ICE than CON in both sexes. Tre, Tsk, HR, sweat rate and TS did not differ between sexes. TC and RPE in ICE were significantly higher during exercise in males than in females. In conclusion, there were no sex differences in the effects of pre-cooling with ice slurry ingestion; however, pre-cooling with ice slurry may be more effective in mitigating ratings of TC and RPE in females than males.