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From the Subarctic to the Tropics: Effects of 4-Month Deployment on Soldiers' Heat Stress, Heat Strain, and Physical Performance

Rintamäki, Hannu1,2; Kyröläinen, Heikki3; Santtila, Matti4; Mäntysaari, Matti5; Simonen, Riitta6; Torpo, Henna6; Mäkinen, Tero1; Rissanen, Sirkka1; Lindholm, Harri6

Journal of Strength & Conditioning Research:
doi: 10.1519/JSC.0b013e31825d817e
Original Research
Abstract

Abstract: Rintamäki, H, Kyröläinen, H, Santtila, M, Mäntysaari, M, Simonen, R, Torpo, H, Mäkinen, T, Rissanen, S, and Lindholm, H. From the subarctic to the tropics: effects of 4-month deployment on soldiers' heat stress, heat strain, and physical performance. J Strength Cond Res 26(7): S45–S52, 2012—The aim of the study was to evaluate the heat stress of Finnish male soldiers (N = 20, age 22.0 ± 2.5 years, body mass 78.8 ± 11.5 kg, and height 180.2 ± 5.6 cm) during their 4-month deployment in a hot environment and to find out the effects on physical performance and body composition. The troops moved from 2.5° C (mean monthly temperature) in Finland to 31.9° C in Chad. During the deployment, temperatures varied between 13.5 and 57.0° C outdoors and in the vehicles and tents. During 1-day recording in the middle of the deployment, skin temperatures were 34–35° C during daytime and maximal core temperature remained mainly below 38.0° C. Body mass decreased (78.4 ± 11.5 kg vs. 75.6 ± 8.6, p = 0.007) during the deployment without changes in fat mass. The sit-up performance increased by 10.9% (46 ± 10 reps·min−1 vs. 51 ± 7 reps·min−1, p < 0.01), and the maximal force production of the leg extensor muscles increased (3,042 ± 614 N vs. 3,277 ± 706 N, p < 0.05) without change in the rate of force development. No changes were observed in the push-ups, repeated squats, maximal grip strength, and running distance during the 12-minute test. In conclusion, the soldiers were able to maintain or improve their physical performance during the deployment despite the heat stress. It is important to encourage soldiers to engage in physical training, especially during a thermally appropriate time of the day or in air-conditioned facilities. Monitoring of local heat stress is also recommended.

Author Information

1Finnish Institute of Occupational Health, Oulu, Finland

2Institute of Biomedicine, Department of Physiology, University of Oulu, Oulu, Finland

3Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, Finland

4Personnel Division, Defence Command, Finnish Defence Forces, Helsinki, Finland

5Aeromedical Center, Center for Military Medicine, Helsinki, Finland

6Finnish Institute of Occupational Health, Helsinki, Finland

Address correspondence to Hannu Rintamäki hannu.rintamaki@ttl.fi.

Copyright © 2012 by the National Strength & Conditioning Association.