Neuromuscular Performance and Hormonal Profile During Military Training and Subsequent Recovery Period.

INTRODUCTION: Military training loads may induce different physiological responses in garrison and field training and only a little is known about how short-time recovery, lasting a few days, affects neuromuscular fitness and hormonal profile. This study aimed to investigate the effects of garrison and field military service on neuromuscular performance and hormonal profile and to evaluate the effects of a 3-day recovery on those factors. METHODS: Twenty healthy male soldiers (20 ± 1 years) participated in the study, which consisted of 4 days of garrison training [days (D) 1-4] and 7 days of military field training (Days 5-12) followed by a 3-day recovery period (Day 15). Serum hormone concentrations [testosterone (TES), cortisol (COR), sex-hormone binding globulin (SHBG), free thyroxine (T4)] were assessed at D1, D5, D8-12, and D15. Handgrip strength was measured in 10 participants at D1, D5, D8, D12, and D15. Maximal isometric force, electromyography, and rate of force development (RFD) of the knee extensors and arm flexors were also measured at D5, D12, and D15. RESULTS: The maximal force of both the arm flexors and knee extensors was not affected by the garrison or field training, whereas the RFD of the knee extensors was decreased during the field training (D5: 383 ± 130 vs. D12: 321 ± 120 N/s, p < 0.05). In addition, handgrip strength was mostly no affected, although a significant difference was observed between D8 and D12 (531 ± 53 vs. 507 ± 43 N, p < 0.05) during the field training. TES decreased already during the garrison training (D1: 18.2 ± 3.9 vs. D5: 16.2 ± 4.0 nmol/L, p < 0.05) and decreased further during the field training compared to baseline (D8: 10.2 ± 3.6 - D11: 11.4 ± 5.4 nmol/L, p < 0.05) exceeding the lowest concentration in the end of the field training (D12: 7.1 ± 4.1 nmol/L, p < 0.05). Similar changes were observed in free TES (D1: 72.2 ± 31.4 vs. D12: 35.1 ± 21.5 nmol/L, p < 0.001). The TES concentration recovered back to the baseline level and free TES increased after the recovery period compared with the baseline values (D15: 19.9 ± 5.3 nmol/L, D15: 99.7 ± 41.1 nmol/L, respectively). No changes were observed in the COR or SHBG concentrations during the garrison period. COR was decreased in the end of the field training (D12: 388 ± 109 nmol/L) compared with baseline (D1: 536 ± 113 nmol/L) (p < 0.05-0.001) but recovered back to the baseline levels after the recovery period (D15: 495 ± 58 nmol/L), whereas SHBG linearly increased towards the end of the field training (p < 0.05-0.001). CONCLUSIONS: The present findings demonstrate that neuromuscular performance can be relatively well maintained during short-term garrison and field training even when a clear decrease in hormonal profile is evident. In addition, hormonal responses during field training seem to be greater compared to garrison training, however, the recovery of 3-day in free-living conditions seems to be sufficient for hormonal recovery. Therefore, a short-term recovery period lasting few days after the military field training may be required to maintain operational readiness after the field training.

Association with physical fitness, serum hormones and sleep during a 15-day military field training.

The present study aimed to investigate the association between physical fitness, sleep duration and hormonal responses during a 15-day military field training (MFT). The purpose of MFT was to practice offensive manoeuvres in a countryside area. Nine army officers volunteered to participate, and their daily working routine mainly consisted of tasks in the headquarters that required on-call-duty at all times. Physical fitness and body composition were measured just before MFT. Serum testosterone (TES) and cortisol (COR) concentrations and sex-hormone-binding globulin (SHBG) were measured before MFT, as well as 8 and 15 days after the beginning of MFT. Heart rate (HR) was recorded for approximately 24 h on days 8, 11 and 15 of MFT. Based on HR responses, there was no evidence of cardiorespiratory strain, hormonal responses or energy deficit during MFT. Although the changes in hormonal concentrations were insignificant, they were well correlated with physical fitness (r=0.67, p=0.05). Furthermore, the TES/SHGB ratio decreased by 28% in subjects whose VO2max was under 44 ml kg(-1) min(-1). On average, subjects slept for 6.20 h per day, but the sleeping rhythm was disturbed due to military tasks. This diurnal sleeping time was strongly associated with TES/COR ratio (r=0.78, p=0.01). These results indicate that MFT causes very individual stress reactions, despite the low levels of physical strain and energy deficit. We therefore concluded that the observed hormonal responses were mainly due to sleep deprivation and low physical fitness.