Neuromuscular Performance Changes in Response to the Australian Special Forces Selection Course

Strenuous military activities, such as Special Forces (SF) selection courses, are known to involve high physical loads in the presence of food and sleep deprivation, which can have detrimental impacts on physical performance. Understanding the magnitude of performance deficit and the time required for recovery associated with these events, is important for injury prevention and maintaining operational readiness. The purpose of this study was to investigate the changes in physical performance in response to the Australian SF Selection Course (SF-SC) and to monitor recovery throughout 8 weeks following the course.

Ninety-three healthy male participants (age: 28 ± 4 years) were recruited; follow-up data were available from those who successfully completed the SF-SC (n = 21). The isometric mid-thigh pull (IMTP), countermovement jump (CMJ), serum hormone concentrations (total testosterone, free testosterone, cortisol, sex hormone binding globulin [SHBG], testosterone:cortisol ratio [T:C]), and body composition (body mass, lean mass) were assessed before the course, immediately post-course, and at 1, 3, 5, and 8 weeks post-course. This study employed Wilcoxon rank tests for pairwise comparisons between baseline and immediate post-course measures, as well as baseline measures with subsequent time points (weeks 1, 3, 5, and 8) to assess recovery time. Additionally, linear mixed effects models (LMEs) were used to analyze the effects of body composition and hormones on physical performance.

IMTP peak force was reduced by 16 ± 11% (P < .01, ES = 0.83, 95% CI [0.66-0.88]), and peak force relative to lean mass was reduced by 13 ± 13% (P < .05, ES = 0.76, 95% CI [0.54-0.88]) in response to the SF-SC. No other measured IMTP variable demonstrated statistically significant change in response to the SF-SC, and all measured IMTP variables had returned to baseline levels at 1 week post-course. Jump height was reduced by 28 ± 9% (P < .001, ES = 0.88, 95% CI [0.88-0.88]) in response to the SF-SC. CMJ peak power and mean power were reduced by 30 ± 5.6% (P < .001, ES = 0.88, 95% CI [0.88-0.88]), and 29 ± 7.5% (P < .001, ES = 0.88, 95% CI [0.88-0.88]), respectively. Concentric peak force was reduced by 26 ± 10% (P < .001, ES = 0.88, 95% CI [0.88-0.88]), breaking peak force by 28 ± 26.3% (P < .01, ES = 0.86, 95% CI [0.76-0.88], and flight time:contraction time (F:T) by 26 ± 10.8% (P < .001, ES = 0.88, 95% CI [0.88-0.88]). CMJ variables took between 1 and 3 weeks to recover to baseline. LMEs demonstrated that total testosterone, free testosterone, and the T:C ratio all had a significant effect on CMJ jump height and peak power and IMTP peak force and peak rate of force development (RFD). Body mass and lean mass exhibited significant positive effects on peak power and peak force, while they did not influence jump height or peak RFD.

The SF-SC resulted in large decreases in strength and power, that took 3 weeks to fully recover. The results of this study can be utilized to inform training and recovery intervention following highly strenuous military training.