Influence Of Tyrosine On Body Temperature And Perceptual Responses To Cold Water Immersion In Military Cold-weather Medicine Trainees

Abstract

Cold stress often results in physical and cognitive performance decrements. Tyrosine supplementation may attenuate deficits due to its ability to synthesize and maintain appropriate levels of brain catecholamines. However, the influence of tyrosine on physiological and perceptual responses to cold water immersion has not been reported. PURPOSE: Determine the influence of tyrosine supplementation on physiological and perceptual responses to cold water immersion during a military field training exercise. METHODS: Military personnel (n = 14; age: 26 ± 7 y; body fat: 20.1 ± 8.5%) completed a field training exercise that included a 10-min, head-out, cold water (1.5 °C) immersion in cold air (4 °C). In a randomized, double-blind design, prior to immersion (range 30-120 min), participants ingested either a food bar with 150 mg/kg of body weight of supplemental tyrosine (TYR; n = 7) or placebo (PLA; n = 7). TYR and PLA food bars were matched for taste, texture, and color. Prior to, during, and after immersion, participants’ heart rate (HR), hand temperature (Thand), skin temperature (Tsk), and core temperature (Tc) were measured while ratings of thermal sensation (TS) and shivering sensation (SS) were obtained throughout the exercise. Comparisons between TYR and PLA were made using an analysis of variance with significance set at p < 0.05. RESULTS: Oral tyrosine supplementation improved Tc maintenance, with the greatest difference between TYR and PLA evidenced at 10 min after completion of immersion (TYR: 36.7 ± 0.5, PLA 35.7 ± 0.8 °C, p < 0.05). No differences were observed between TYR and PLA for HR (p = 0.284), Thand (p = 0.693), Tsk (p = 0.947), TS (p = 0.262), or SS (p = 0.068). CONCLUSION: Findings suggest that tyrosine supplementation improved Tc maintenance in response to cold water immersion. However, tyrosine supplementation had minimal influence on thermal perceptions and did not modify HR or Tsk prior to, during, or after immersion. The conservation of core temperature associated with tyrosine supplementation is consistent with other reports, and its mechanisms of action warrant further investigation. This information is critical for deeper understanding of the complex physiological responses to environmental extremes in order to optimize strategies to sustain or enhance human performance in cold environments.