Hormonal, Immunological And Neuromuscular Responses During 21 Days Of Military Field Training

Abstract

Military field training (MFT) exposes warfighters to multiple stressors such as prolonged and strenuous physical activity, sleep deprivation and energy deficit. This has been shown to lead changes in a hormonal profile and decreased physical performance. PURPOSE: To determine the warfighters’ hormonal and neuromuscular responses during a 21-day MFT. METHODS: 49 (age 20±1yrs., height 179±7cm, body mass 73.0±8.7kg) male conscripts participated in the study. Blood samples were drawn and assayed for testosterone (TES), cortisol (COR), insulin-like growth factor 1 (IGF-1), sex hormone binding globulin (SHBG), leptin (LEP), interleukin 1β (IL-1β), interleukin 6 (IL-6) and tumor neurosis factor alpha (TNF-α). Also body composition, maximal isometric force (MVC) from the upper and lower extremities, standing long jump and shooting were measured 4 times during the study. Physical activity (PA) was monitored throughout the 21-day MFT. Daily diaries were collected to follow the workload and mood states of the conscripts. RESULTS: There were significant declines after MFT in TES (11.4%), IGF-1 (21.0%) and LEP (44.4%) and increases in COR (32.0%) and in SHBG (16.3%). In the beginning of MFT, TNF-α increased but decreased in the end and returned to the pre measurement value after the recovery. The same tendency was also found for IL-1β and IL-6. Body mass and fat mass decreased after MFT but recovered during the 4-day recovery period. There was a significant decrease in a standing long jump after MFT and also after the recovery period as compared to the preMFT values. There were no significant changes in MVC during MFT. PA was greater in MFT and the conscripts felt MFT more demanding both physically and mentally than actions in the garrison environment. CONCLUSION: The present study demonstrated slight decrements in warfighter physical performance during the 21-day MFT. Although the conscripts were overloaded during MFT, 4 days of recovery seemed to be enough to obtain the pre measurement values in neuromuscular performance and measured serum hormonal and immunological parameters. The results suggest that it is important to have sufficient recovery time after long MFT to return combat readiness.