Is there differences in physical response and recovery between women and men after demanding military field exercises?

Demanding military field exercises are characterized by very high activity levels often, combined with insufficient food intake and sleep. Previous research has shown that such exercises lead to loss of both body mass, body fat and muscle mass, as well as changes in blood biomarkers and detrimental decline in physical performance. Previous research includes almost only men, and with gender-neutral conscription in the Armed Forces, more knowledge is needed on how women respond on such exercises. In addition, there is little knowledge about how both sexes recover after such exercises. This report includes the results from two different field studies conducted during a moderately and an extremely demanding military field exercise. The purpose was to investigate the acute response and restitution in men and women. To answer the objectives, body composition, blood biomarkers and physical performance were measured before and in the period after the field exercises.

The moderately demanding field exercise lead to a decline in body mass and body fat in both sexes. There were no changes in muscle mass. The women had recovered their body mass after 72 hours, but not the men. Both sexes had reductions in body fat after 72 hours restitution, with no sex differences. There were small or no changes in blood biomarkers.

The extremely demanding field exercise lead to a decline in body mass and body fat in both sexes, but only the men lost muscle mass. The decline in body and muscle mass was greater in men than in women. All changes in body mass were recovered after one week. There were major changes in blood biomarkers, among others a reduction in anabolic hormones such as growth hormone, and an increase in stress hormone and in muscle damage protein. After one week, most of the blood biomarkers were recovered except the stress hormone cortisol, which stayed elevated in women after two weeks.

In the moderately demanding field exercise, the only change in the physical performance was a decline in the lower-body explosive strength in men, which was still reduced after 72 hours recovery. There were no sex differences in physical performance during this exercise.

During the extremely demanding field exercise, the explosive strength in lower and upper body, as well as the ability to perform intense short-term activity (anaerobe capacity) were reduced in both sexes. The upper-body strength and the anaerobe capacity were recovered after two weeks, but the lower-body strength was still reduced. Men had a larger reduction in performance than women.

An extremely demanding field exercise led to changes in body composition, blood biomarkers and physical performance in both sexes. The responses were mostly equal between the sexes, but the men lost more muscle mass and recovered the explosive lower-body strength slower than women. A moderately demanding exercise led to small changes in body composition and blood biomarkers and only minor changes in performance, and there were no sex differences. This shows that the negative physiological changes in the body after field exercises can be significantly reduced with enough rest and food.