Abstract
To investigate sex differences in the effect of a military field exercise on physical performance, body composition, and blood biomarkers. Measurements were done in 23 male and 12 female conscripts before, and 0, 1, 3, 7, and 14days after a 6-day military field exercise. During the field exercise, body mass decreased more in men (-6.5±1.1kg) than in women (-2.7±0.7kg), and muscle mass decreased only in men (-2.7±1.0kg). Body composition recovered within one week. Performance decreased, with no differences between men and women for countermovement jump (CMJ,-19±8 vs. -18±11%), medicine ball throw (MBT, -11±7 vs. -11±7%), and an anaerobic performance test (EVAC, -55±22 vs. -47±31%, men and women, respectively). MBT and EVAC performance recovered within two weeks, whereas CMJ performance was still reduced in men (-17±6%) and women (-9±8%) after two weeks recovery, with a larger reduction in men. Both men and women decreased [IGF-1] (-28±9 vs. -41±8%) and increased [cortisol] (26±26 vs. 66±93%, men and women, respectively) during the exercise. Most biomarkers returned to baseline values within one week. Men lost more body mass and muscle mass than women during a field exercise, but these differences did not lead to sex differences in changes in explosive strength and anaerobic performance. However, women recovered explosive strength in the legs faster than men.
Highlights
An important part of military training is simulated combat training and demanding field exercises
The large reduction in muscle mass might be related to decreases in anabolic hormones and increased catabolic hormones since studies report a large decrease in testosterone and insulin-like growth factor 1 (IGF-1), and increases in cortisol, after field exercises.[1,4,8]
The aims of this study were twofold: Firstly, to investigate sex differences in the acute effects of an extremely demanding military field exercise on explosive strength and anaerobic performance, body composition and blood biomarkers related to body composition and physical performance; secondly, to examine the recovery in both men and women and investigate if there are any sex differences in the recovery process
Summary
An important part of military training is simulated combat training and demanding field exercises. These field exercises often involve very high activity levels and energy expenditure combined with low energy intake and lack of sleep.[1,2,3] Previous studies show that energy expenditure during field exercises can be 5000-10 000 kcal per day, with an energy deficit as high as 5000-6000 kcal per day over a three to seven days period.[2,4,5,6] Such field exercises have been reported to lead to 3%-10% loss of body mass, 7%-28% loss of body fat, and 2%-6% loss of muscle mass,[1,4,7,8] together with detrimental. The large reduction in muscle mass might be related to decreases in anabolic hormones and increased catabolic hormones since studies report a large decrease in testosterone and insulin-like growth factor 1 (IGF-1), and increases in cortisol, after field exercises.[1,4,8] The reduced physical performance has been speculated to be associated with these changes in body composition and hormones,[1,5,8] and to muscle damage[4] as studies report large increases in the muscle damage marker creatine kinase (CK) after demanding field exercises.[2,4]
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