Effect of wearing an ice cooling jacket on repeat sprint performance in warm/humid conditions.

Objective-The purpose of this study was to examine the effect of cooling the skin with an ice jacket before and between exercise bouts (to simulate quarter and half time breaks) on prolonged repeat sprint exercise performance in warm/humid conditions. Methods- After an initial familiarisation session, seven trained male hockey players, performed two testing sessions (seven days apart), comprising an 80 min intermittent, repeat sprint cycling exercise protocol inside a climate chamber set at 30oC and 60% relative humidity. On one occasion a skin cooling procedure was implemented (in random counterbalanced order), with subjects wearing an ice cooling jacket both before (for 5min), and in the recovery periods (2x 5min and 1x 10min) during the test. Measures of performance (work done and power output on each sprint), heart rates, blood lactate concentrations, core (rectal) and skin temperatures, sweat loss, perceived exertion, ratings of thirst, thermal discomfort and fatigue were obtained in both trials.Results- In the cooling condition, chest (torso) skin temperature, thermal discomfort and rating of thirst were all significantly lower (p<0.05), but no statistical significance (p>0.05) was observed between conditions for measures of work done, power output, heart rate, blood lactate concentration, core or mean skin temperature, perceived exertion, sweat loss, or ratings of fatigue. However, high effect sizes indicated trends for lowered lactate concentrations, sweat losses and mean skin temperatures in the cooling condition. Conclusions- In the present study the intermittent use of an ice cooling jacket, both before and during a repeat sprint cycling protocol in warm/humid conditions did not improve physical performance, although the perception of thermal load was reduced. Longer periods of cooling both prior to and during exercise (to lower mean skin temperature by a greater degree than observed here) may be necessary to produce such a change.