CRUSHED-ICE INGESTION LOWERS THERMAL STRESS AND IMPROVES EXTENSIVE PERFORMANCES

Peeling, P., Ihsan, M., & Landers, G. (2009). The effect of crushed ice on 40 km cycling time-trial performance. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

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"Pre-cooling is a temperature regulation strategy whereby core temperature is lowered prior to exercise, and has been consistently shown to improve endurance capacity and athletic performance. However, pre-cooling protocols such as water immersion and cold air exposure are time consuming, logistically demanding and in some instances may result in adverse thermal responses, making these conventional methods impractical as a pre-event strategy. Endogenous cooling methods (i.e. fluid ingestion) have been shown to attenuate the rise in core temperature during exercise. Despite the positive effects of fluid ingestion on core temperature responses to exercise, the effect of fluid temperature has been less studied."

This study examined the effect of crushed-ice ingestion as a pre-cooling method on body temperature responses and cycling time-trial performance. Trained male athletes (N = 7) completed a familiarization, and two experimental 40-km cycling time-trials on a wind-braked cycle ergometer in a climate controlled chamber, set to 30C and 75% relative humidity. The two experimental cycling time-trials included one trial preceded by a 30-minute period of thermoneutral (~26.8C) water consumption (the control condition), and the other by a 30-minute period of pre-cooling via crushed ice (~1.4C) consumption. The fluid volumes in each trial amounted to 6.8 g/kgBM. The order of trial completion was randomized, counterbalanced and completed within 14 days following the initial session. Each 40-km time-trial required Ss to complete 1,200 kJ of work in the fastest time possible. During the trials, skin temperature, core temperature, cycling performance time, power output, heart rate, blood lactate, ratings of perceived exertion, and ratings of thermal sensation were measured at set intervals of work.

Pre-cooling with ice lowered the core temperature significantly more than in the water-consumption control condition. This difference remained evident until 200 kJ of work was completed in the time-trial task. Time-trial completion time was 6.5% faster with ice ingestion when compared to water ingestion. No significant differences existed between conditions at any time point of the time-trials for skin temperature, heart rate, or ratings of perceived exertion. The ratings of thermal sensation were significantly higher in the water-ingestion condition at 200 kJ of cycling compared to the ice condition. Ice ingestion was effective in lowering core temperature and improved subsequent 40 km cycling performance in a hot/humid environment. A reduced thermal strain was evident in the ice condition compared to the control condition at the start of the time-trial. Split time data indicated that the latter parts of the time-trial (900-1100 kJ) were significantly faster in the ice condition compared to the water condition despite no significant differences in heart rate, blood lactate, core temperature, ratings of perceived exertion, or ratings of thermal perception. The lower thermal strain evident in the ice condition compared to the control at the start of the time-trial may have provided a greater heat storage capacity and muscle energy reserve that was used towards the end of the time trial, resulting in enhanced performance.

Implication. Pre-exercise ingestion of crushed ice is an effective way of lowering thermal stress and results in performance enhancement in extended cycling tasks.

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