The Finnish military conducted a study on soldiers completing a 15 day field exercise in 2010 (Tyyska et al 2010). Before the exercise, the soldiers’ fitness, body composition, serum testosterone, cortisol and sex hormone binding globulin were measured. These measurements were taken again on day 8 and 15 of the field exercise. On day 8, 11 and 15 the soldiers wore a heart rate monitor for 24hrs. It was demonstrated that those with VO2s under 44ml/kg/min had worse serum testosterone to sex hormone binding globulin ratios and higher serum testosterone to cortisol ratios. This would tend to indicate that even in low intensity activity such as field craft, when sleep is compromised it has a major effect on the body’s hormones. Overall body endurance is strongly correlated to one’s VO2max and even in non-stressful activities, if you’re VO2 is poor, it appears your capabilities will be compromised. If you are having problems recovering and your nutrition and sleep are dialed in (the main culprits when recovery is a key), a cycle of endurance work for VO2 capacity may be in order before you return to your primary activity.