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Ed Maunder, Paul B. Laursen and Andrew E. Kilding

Purpose:

To compare the physiological and performance effects of ad libitum cold-fluid (CF) and ice-slurry (IS) ingestion on cycling time-trial (TT) performance in the heat.

Methods:

Seven well-trained male triathletes and cyclists completed 2 maximaleffort 40-km cycling TTs in hot (35°C) and humid (60% relative humidity) conditions. In randomized order, participants ingested CF or IS (initial temperatures 4°C and –1°C, respectively) ad libitum during exercise. At each 5-km interval, time elapsed, power output, rectal and skin temperature, heart rate, and perceptual measures were recorded. The actual CF and IS temperatures during the 40-km TT were determined post hoc.

Results:

Performance time (2.5% ± 2.6%, ES = 0.27) and mean power (–2.2% ± 3.2%, ES = –0.15) were likely worse in the IS trial. Differences in thermoregulatory and cardiovascular measures were largely unclear between trials, while feeling state was worse in the later stages of the IS trial (ES = –0.31 to –0.95). Fluid-ingestion volume was very likely lower in the IS trial (–29.7% ± 19.4%, ES = –0.97). The temperatures of CF and IS increased by 0.37°C/min and 0.02°C/min, respectively, over the mean TT duration.

Conclusions:

Ad libitum ingestion of CF resulted in improved 40-km cycling TT performance compared with IS. Participants chose greater fluid-ingestion rates in the CF trial than in the IS trial and had improved feeling state. These findings suggest that ad libitum CF ingestion is preferable to IS during cycling TTs under conditions of environmental heat stress.

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Koen Levels, Lennart P.J. Teunissen, Arnold de Haan, Jos J. de Koning, Bernadet van Os and Hein A.M. Daanen

Purpose:

The best way to apply precooling for endurance exercise in the heat is still unclear. The authors analyzed the effect of different preparation regimens on pacing during a 15-km cycling time trial in the heat.

Methods:

Ten male subjects completed four 15-km time trials (30°C), preceded by different preparation regimes: 10 min cycling (WARM-UP), 30 min scalp cooling of which 10 min was cycling (SC+WARM-UP), ice-slurry ingestion (ICE), and ice slurry ingestion + 30 min scalp cooling (SC+ICE).

Results:

No differences were observed in finish time and mean power output, although power output was lower for WARM-UP than for SC+ICE during km 13–14 (17 ± 16 and 19 ± 14 W, respectively) and for ICE during km 13 (16 ± 16 W). Rectal temperature at the start of the time trial was lower for both ICE conditions (~36.7°C) than both WARMUP conditions (~37.1°C) and remained lower during the first part of the trial. Skin temperature and thermal sensation were lower at the start for SC+ICE.

Conclusions:

The preparation regimen providing the lowest body-heat content and sensation of coolness at the start (SC+ICE) was most beneficial for pacing during the latter stages of the time trial, although overall performance did not differ.

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Emiel Schulze, Hein A.M. Daanen, Koen Levels, Julia R. Casadio, Daniel J. Plews, Andrew E. Kilding, Rodney Siegel and Paul B. Laursen

Purpose:

To determine the effect of thermal state and thermal comfort on cycling performance in the heat.

Methods:

Seven well-trained male triathletes completed 3 performance trials consisting of 60 min cycling at a fixed rating of perceived exertion (14) followed immediately by a 20-km time trial in hot (30°C) and humid (80% relative humidity) conditions. In a randomized order, cyclists either drank ambient-temperature (30°C) fluid ad libitum during exercise (CON), drank ice slurry (−1°C) ad libitum during exercise (ICE), or precooled with iced towels and ice slurry ingestion (15g/kg) before drinking ice slurry ad libitum during exercise (PC+ICE). Power output, rectal temperature, and ratings of thermal comfort were measured.

Results:

Overall mean power output was possibly higher in ICE (+1.4% ± 1.8% [90% confidence limit]; 0.4 > smallest worthwhile change [SWC]) and likely higher PC+ICE (+2.5% ± 1.9%; 1.5 > SWC) than in CON; however, no substantial differences were shown between PC+ICE and ICE (unclear). Time-trial performance was likely enhanced in ICE compared with CON (+2.4% ± 2.7%; 1.4 > SWC) and PC+ICE (+2.9% ± 3.2%; 1.9 > SWC). Differences in mean rectal temperature during exercise were unclear between trials. Ratings of thermal comfort were likely and very likely lower during exercise in ICE and PC+ICE, respectively, than in CON.

Conclusions:

While PC+ICE had a stronger effect on mean power output compared with CON than ICE did, the ICE strategy enhanced late-stage time-trial performance the most. Findings suggest that thermal comfort may be as important as thermal state for maximizing performance in the heat.

Open access

Alan J. McCubbin, Bethanie A. Allanson, Joanne N. Caldwell Odgers, Michelle M. Cort, Ricardo J.S. Costa, Gregory R. Cox, Siobhan T. Crawshay, Ben Desbrow, Eliza G. Freney, Stephanie K. Gaskell, David Hughes, Chris Irwin, Ollie Jay, Benita J. Lalor, Megan L.R. Ross, Gregory Shaw, Julien D. Périard and Louise M. Burke

change a solid into liquid ( Jay & Morris, 2018 ; Ross et al., 2013 ), ice-slurry beverages allow for a greater heat storage capacity and level of thermal comfort than a similar volume of ingested fluid ( Ihsan et al., 2010 ; Siegel et al., 2010 ; Siegel et al., 2011 ). Adding glycerol and other

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Jacinta M. Saldaris, Grant J. Landers and Brendan S. Lay

, cardiovascular function and cognitive performance in the heat . Eur J Appl Physiol . 2008 ; 104 : 271 – 280 . doi: 10.1007/s00421-008-0677-y 18214520 13. Vanden Hoek T , Kasza K , Beiser D , et al . Induced hypothermia by central venous infusion: saline ice slurry versus chilled saline . Crit Care

Open access

Louise M. Burke, Asker E. Jeukendrup, Andrew M. Jones and Martin Mooses

precooling with ice slurry in addition to external cooling strategies if a significant thermal challenge is anticipated Consider prerace precooling with ice slurry in addition to external cooling strategies if a significant thermal challenge is anticipated Consider prerace hyperhydration if a large fluid

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Matthew Zimmermann, Grant Landers, Karen Wallman and Georgina Kent

. Med Sci Sports Exerc . 2011 ; 43 ( 1 ): 123 – 133 . PubMed doi:10.1249/MSS.0b013e3181e93210 20508537 10.1249/MSS.0b013e3181e93210 14. Siegel R , Mate J , Brearley MB , Watson G , Nosaka K , Laursen PB . Ice slurry ingestion increases core temperature capacity and running time in the

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Steve H. Faulkner, Iris Broekhuijzen, Margherita Raccuglia, Maarten Hupperets, Simon G. Hodder and George Havenith

. Precooling can be applied via a variety of methods, some of which are more applicable in the field than others. Two of the most common methods include the use of cooling vests, 9 ice slurries, 10 or via a combination of internal and external methods. 11 Tyler et al 8 provide an excellent overview of the

Open access

Douglas J. Casa, Samuel N. Cheuvront, Stuart D. Galloway and Susan M. Shirreffs

. Ingestion of ice slurry before exercise is an alternative hydration strategy, but appears no more effective than cold water and may produce untoward side effects ( Jay & Morris, 2018 ). The practice of trying to delay dehydration by expanding total body water using beverages with high salt concentrations or

Open access

Timothy M. Wohlfert and Kevin C. Miller

, Maté J , Watson G , Nosaka K , Laursen PB . Pre-cooling with ice slurry ingestion leads to similar run times to exhaustion in the heat as cold water immersion . J Sports Sci . 2012 ; 30 : 155 – 165 . PubMed ID: 22132792 doi:10.1080/02640414.2011.625968 10