The Effects of a 10-day Military Field Exercise on Body Composition, Physical Performance, and Muscle Cells in Men and Women

ABSTRACT Purpose To investigate the effects of a demanding military field exercise on physical performance, body composition and muscle cellular outcomes in men and women. Methods Ten men (20.5 ± 0.5 years) and 8 women (21.4 ± 1.4 years) completed a 10-day field exercise consisting of extensive physical activity with food and sleep restriction. Acquisition of body composition, physical performance, blood and muscle biopsies samples were done before and 1,7 and 14 days after the exercise. Results There were no sex differences in the response to the exercise. Body mass was decreased with 5.6 ± 1.8% and fat mass with 31 ± 11% during the exercise. Both were still reduced after 14 days (2.5 ± 2.3%, p ˂0.001 and 12.5 ± 7.7%, p ˂0.001 respectively). Isometric leg strength did not change. Peak leg extension torque at 240 °·s -1 and counter movement jump height were reduced with 4.6 ± 4.8% ( p = 0.012) and 6.7 ± 6.2% ( p ˂0.001) respectively and was still reduced after 14 days (4.3 ± 4.2%, p = 0.002, and 4.1 ± 4.7%, p = 0.030). No changes occurred in fiber CSA, fiber types, proteins involved in calcium handling or HSP70. During the exercise, αB-crystallin levels decreased by 14 ± 19% ( p = 0.024) in the cytosolic fraction and staining intensity on muscle sections tended to increase (17 ± 25%, p = 0.076). MuRF1 levels in the cytosolic fraction tended to decrease (19 ± 35%) and increased with 85 ± 105% ( p = 0.003) in the cytoskeletal fraction 1 week after the exercise. Conclusions The field exercise resulted in reduced body mass and physical performance in both sexes. The ability to produce force at high contraction velocities and explosive strength was more affected than isometric strength, but this was not related to any changes in fiber type composition, fiber area, Ca 2+ handling or fiber type specific muscle damage.