Cold acclimation does not improve cycling performance

Purpose: Warfighters must be able to move and react quickly to ever changing threats and hostile situations in all types of environments. In cold environments, deterioration of physical performance occurs due to reduced muscle contractility and efficiency resulting from cold muscles. Shivering thermogenesis also fatigues muscles and uses valuable energy stores, further limiting physical performance. Cold acclimation, however, improves insulation and reduces shivering, leading to greater heat retention while minimizing energy expenditure. Therefore, it is possible that cold acclimation could improve physical performance by keeping muscles warmer and energetically ready to perform. The purpose of this study is to determine the impact that cold acclimation has on physical performance. Methods: Twelve healthy subjects (age: 25.6 ± 5.2 y, height: 174.0 ± 8.9 cm, weight: 75.6 ± 13.1 kg) first performed a 20-minute baseline cycling test in 22 ◦C, 40% humidity without prior cold exposure. Twenty-four hours later they began a 7-day cold acclimation protocol, consisting of 90-minute, once daily, cold water immersions (10 ◦C, immersed to mid-sternum). Following each immersion, subjects exited the water, dried off, and remained seated for 60 minutes. On days one, four, and seven of the cold acclimation protocol, subjects completed the same 20-minute cycling test in 22 ◦C, 40% humidity, after sitting for 60 minutes following the immersion. Measurements of mechanical work completed, core and skin temperatures, heart rate, skin blood flow, perceived exertion, and thermal sensation were measured during each cycling test. Results: Subjects experienced a reduction in shivering and an enhanced vasoconstriction response, supporting a successful acclimation to cold. Although perceived exertion was similar between all four cycling tests, the amount of mechanical work produced during the baseline cycling test (220 ± 70 kJ) was greater (p < 0.001) than all three cycling tests that were performed following immersions (195 ± 58, 197 ± 60, and 194 ± 62 kJ), suggesting that cold exposure deteriorated cycling performance. However, this impairment was not attenuated over the cold acclimation period. Conclusions: Findings from this study show that cycling performance is impaired following cold water immersion. Results also suggest that a 7-day cold acclimation protocol does not improve cycling performance. Therefore, warfighters and military commands looking to enhance physical performance in cold environments should seek other techniques to attenuate physical performance impairments that are observed following severe cold stress.