Medicine & Science in Sports & Exercise:
E-27 Free Communication/Poster - Cold Stress: JUNE 4, 2010 7:30 AM - 12:30 PM: ROOM: Hall C
Johnson, Evan C.; May, Courtney A.; Wong, Janine M.; Jameson, Jason T.; Hodgdon, James A. FACSM; Heaney, Jay H.
Naval Health Research Center, San Diego, CA.
(No disclosure reported)
Hypothermia incurred during training exposure to cold leads to lost training time and possible injury or death. Certain exercises do not occur in particularly cold atmospheres; however, they may involve water immersion and time out of water in wet clothing. Wet clothing results in greater conductive, convective, and evaporative heat loss than dry clothing. This may contribute to hypothermia.
PURPOSE: To observe trainee gastro-intestinal temperature (TGI) responses that occur in different water and air conditions and how these responses may be helpful to monitor trainees' safety.
METHODS: TGI responses were measured on three occasions (E1, E2, and E3) using an ingestible thermistor consumed > 4hr prior to the first measurement. Group characteristics are as follows: E1 - N=30, height 177 ± 5 cm, body mass 77 ± 7 kg; E2 - N=20, height 177 ± 5 cm, body mass 75 ± 6 kg; E3 - N=69, height 178 ± 7 cm; body mass 77 ± 8 kg. Ambient air temperature (Ta), wind velocity (Vw) and water temperature (Tw) were: E1 14.6°C, 3.3 m·s-1, 15.6°C; E2 14.5°C, 1.0 m·s-1, 17.2°C; E3 19.9°C, 0.5 m·s-1, 18.3°C. The duration of immersion and time on shore in wet clothing were; 38 min, 21 min; 25 min, 12 min; and 33 min, 22min, respectively for E1, E2, and E3.
RESULTS: In all exercises mean TGI significantly decreased from the start of the exercise to the end; E1 37.4 ± 0.4°C to 35.3 ± 0.7°C (p<0.01); E2 37.7 ± 0.4°C to 36.5 ± 0.8°C (p<0.01); E3 37.2 ±.04°C to 36.6 ± 0.5°C (p<0.01). Significantly different mean rates of TGI decrease were observed between E1 (-0.04 ± 0.01 °C·min-1) and E3 (-0.01 ± 0.01 °C·min-1) (p<0.01) as well as between E2 (-0.03 ± 0.02 °C·min-1) and E3 (-0.01 ± 0.01 °C·min-1) (p<0.01). E1 and E2 rates of decrease did not differ.
CONCLUSION: Although the temperatures experienced by the trainees may be considered moderate, rapid cooling rates were observed. Significantly different rates of TGI decrease between E2 and E3 despite experiencing similar Tw emphasizes that immersion is not the only aspect of body temperature drop during these exercises. Therefore in order to minimize hypothermic risk and potentially lost training time, exposure guidance for exercises that occur in water as well as on land in wet clothing should incorporate Tw, Ta, and Vw as all these factors may affect the rate of body temperature drop.