Effect of Ice Slurry Ingestion on Cardiovascular Drift and V[Combining Dot Above]O2max during Heat Stress

External body cooling by fan airflow mitigates the decrease in maximal oxygen uptake (V[Combining Dot Above]O2max) associated with cardiovascular (CV) drift during cycling in hot conditions. It remains unknown whether internal body cooling via ice slurry ingestion elicits a similar response. Purpose To test the hypothesis that ice slurry ingestion attenuates the magnitude of CV drift and accompanying decrement in V[Combining Dot Above]O2max during heat stress. Methods Eight men completed a graded exercise test on a cycle ergometer in 22 °C to measure V[Combining Dot Above]O2max. Then on 3 separate occasions (in randomly assigned counterbalanced treatment orders), they cycled at 60%V[Combining Dot Above]O2max in hot conditions (35 °C, 40% RH) for either 15 min, 45 min with tepid (23 °C) fluid ingestion (45FL), or 45 min with ice (-1° C) slurry ingestion (45ICE), followed immediately by measurement of V[Combining Dot Above]O2max. The purpose of the separate 15- and 45-min trials was to measure CV drift and V[Combining Dot Above]O2max over the same time interval. Results The increase in HR between 15 and 45 min was twice as large in 45FL (8.6%) compared to 45ICE (4.6%; P=0.02). SV declined by 6.2% in 45FL but was maintained with 45ICE (P=0.02). V[Combining Dot Above]O2peak decreased from 15 to 45 min by 8.6% and 9.0% in 45FL and 45ICE, respectively, but was not different between conditions (P=0.79). Conclusion While ice slurry ingestion attenuated CV drift more than fluid ingestion, it did not mitigate the decline in V[Combining Dot Above]O2max. Contrary to previous findings, when ice slurry is ingested, changes in HR may not reflect changes in relative metabolic intensity during prolonged exercise in the heat. Corresponding Author: Jason Ng, Ph.D., CSCS, 5500 University Parkway, San Bernardino, CA 92407-2393, Phone: (909) 537-5412, Fax: (909) 537-7085. Email: jason.ng@csusb.edu CSUSB Faculty Center for Excellence for supporting the publication of this paper with funded writing time. The authors declare no conflict of interest. The results of the present study do not constitute endorsement by the American College of Sports Medicine. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. Accepted for Publication: 25 September 2018 © 2018 American College of Sports Medicine

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