Sex differences in effect and recovery of strenuous military field exercises
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Purpose: Recovery and sex differences in response to strenuous military field exercises are largely unknown. The purpose of this study was to investigate the effect of strenuous military field exercises and the course of recovery on body composition and physical performance, and to examine potential sex differences in these responses. Methods: 35 soldiers (23 men and 12 women) from the conscript division at the Norwegian Armed Forces Special Command volunteered to participate. Measurements were conducted before, 0 hours, 24 hours, 72 hours, 1 week and 2 weeks after a strenuous field exercise. Energy expenditure was measured during the exercise by accelerometers. Body composition was measured through bioelectrical impedance analysis (BIA) and physical performance was measured through a countermovement jump (CMJ), medicine ball thrust (MBT) and anaerobic performance through an evacuation test (EVAC-test). Results: The men reduced their body mass and lean body mass (-8.16 ± 0.22 %, p < 0.001 and -6.13 ± 0.38 %, p < 0.001, respectively) more than the women (-3,96 ± 0.31 %, p < 0.001 and -0.36 ± 0.64 %, p = 1.000, respectively) after the field exercise with no different reductions in fat mass (men: 38.80 ± 3.47 %, p < 0.001, women: 27.02 ± 4.80 %, p < 0.001). All changes in body composition had recovered after 1 week. All performance variables were reduced to the same degree in men and women after the selection exercise. CMJ jump height was still reduced in both groups after 2 weeks, and the reduction after 72 hours (men -23.54 ± 6.79 %, p < 0.001, women: 14.33 ± 8.05 %, p = 0.001) and 2 weeks (men: -16.84 ± 6.10 %, p < 0.001, women: 8.88 ± 8.31 %, p = 0.026) was larger in the men compared to the women (p < 0.001). The same pattern of changes and sex differences was found for maximal power during the CMJ. MBT throw distance recovered after 1 week, and EVAC performance after 2 weeks with no differences between the groups. Conclusion: The results show that the men lost more body mass and lean mass than women after a very strenuous military field exercise. Reduction in physical performance after the field exercise was similar between men and women. Both anaerobic capacity and upper body strength had recovered within two weeks. However, explosive strength in the legs was not recovered by two weeks in neither men nor women, and the recovery was slower in men compared to women.
Masteroppgave - Norges idrettshøgskole, 2018