Abstract
Purpose
This study examined the thermoregulatory response and ergogenic effects of ice slurry (ICE) ingestion in hot environments with high and low relative humidity (RH).
Methods
Eight males completed four trials in a crossover manner in dry (DRY: 34.7 ± 0.2 °C, 38 ± 2%RH) and humid heat (HUM: 34.8 °C ± 0.2 °C, 80 ± 1%RH). They ingested 8.0 g·kg−1 of ICE (0.0 °C) or 37.5 °C water (CON) during 30 min before exercise, and three aliquots (3.2 g·kg−1) of ICE or CON during 45-min cycling at 50%\({\dot{\text{V}}}\)O2peak, followed by cycling to exhaustion at 80%\({\dot{\text{V}}}\)O2peak (TTE). Body core temperature (Tcore), mean skin temperature (Tsk), heart rate (HR), thermal comfort, thermal sensation and rating of perceived exertion (RPE) were measured.
Results
Relative to CON, ICE improved TTE by 76.5 ± 96.5% in HUM and 21.3 ± 44.9% in DRY (p = 0.044). End-exercise Tcore was lower in ICE versus CON in DRY (37.8 ± 0.4 °C versus 38.1 ± 0.3 °C, p = 0.005) and HUM (38.8 ± 0.4 °C versus 39.3 ± 0.6 °C, p = 0.004). ICE decreased HR, heat storage and heat strain index only in DRY (p < 0.001–0.018). ICE improved thermal sensation and comfort in DRY and HUM (p < 0.001–0.011), attenuated RPE in HUM (p = 0.012) but not in DRY (p = 0.065).
Conclusion
ICE tended to benefit performance in humid heat more than in dry heat. This is likely due to the reduced extent of hyperthermia in dry heat and the relative importance of sensory inputs in mediating exercise capacity.
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Data availability
All data generated or analysed during this study are included in this published article.
Abbreviations
- BSA:
-
Body surface area
- C + R:
-
Combined heat exchange via convection and radiation
- Cp(fluid) :
-
Specific heat capacity of water
- Cp(ice) :
-
Specific heat capacity of ice
- Cres + Eres :
-
Convective and evaporative heat loss due to respiration
- DRY + CON:
-
37.5 °C water ingestion in hot and dry environment
- DRY + ICE:
-
Ice slurry ingestion in hot and dry environment
- E:
-
Evaporative heat loss
- Emax :
-
Evaporative capacity of the environment
- Ereq :
-
Evaporative requirement for heat balance
- fcl :
-
Clothing area factor
- h:
-
Combined convective and radiative heat transfer coefficient
- hc :
-
Convective heat transfer coefficient
- Hfluid :
-
Heat exchange with ingested fluid
- Hice :
-
Energy lost when ice melts
- Hprod :
-
Metabolic heat production
- HR:
-
Heart rate
- HRdiff :
-
Difference in heart rate between the end of the exercise and immediately before the start of the exercise
- HRmean :
-
Mean heart rate during exercise
- HRpeak :
-
Peak heart rate during exercise
- HSI:
-
Heat strain index
- HUM + CON:
-
37.5 °C water ingestion in hot and humid environment
- HUM + ICE:
-
Ice slurry ingestion in hot and humid environment
- ICE:
-
Ice slurry
- LR:
-
Lewis Relation
- LSR:
-
Local sweat rate
- M:
-
Metabolic energy expenditure
- massfluid :
-
Mass of ingested fluid
- massice :
-
Mass of ingested ice
- Pa :
-
Ambient vapour pressure
- Psk :
-
Saturated vapour pressure at the skin
- Rcl :
-
Heat transfer resistance of clothing
- RER:
-
Respiratory exchange ratio
- RPE:
-
Rating of perceived exertion
- S:
-
Body heat storage
- Ta :
-
Air temperature
- Tcore :
-
Body core temperature
- Tfluid :
-
Ingested fluid temperature
- Tsk :
-
Weighted mean skin temperature
- TTE:
-
Time-to-exhaustion
- USG:
-
Urine specific gravity
- v:
-
Air velocity
- \({\dot{\text{V}}}\)CO2 :
-
Carbon dioxide production
- \({\dot{\text{V}}}\)̇O2 :
-
Oxygen uptake
- \({\dot{\text{V}}}\)̇O2peak :
-
Peak oxygen uptake
- W:
-
Work output
- WBSR:
-
Whole body sweat rate
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Acknowledgements
The experiments were carried out at Singapore Sport Institute. The authors wish to thank all the participants for volunteering.
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HCC, MI, JLKW and SFB conceived and designed the research. HCC, DHWC, KMC, IT and JC conducted the study. HCC, DHWC and MI analysed the data and wrote the manuscript. All authors read and approved the manuscript.
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All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee and the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This study was approved by Institutional Review Boards of Singapore Sport Institute (Reference number: PH-FULL-038) and Nanyang Technological University (Reference number: IRB-2021–242).
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Communicated by Narihiko kondo.
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Choo, H.C., Choo, D.H.W., Tan, I. et al. Effect of ice slurry ingestion on thermoregulatory responses during fixed-intensity cycling in humid and dry heat. Eur J Appl Physiol 123, 2225–2237 (2023). https://doi.org/10.1007/s00421-023-05235-y
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DOI: https://doi.org/10.1007/s00421-023-05235-y