Author(s): KYRÖLÄINEN, H., SEPPÄNEN, J., OJANEN, T., Institution: UNIVERSITY OF JYVÄSKYLÄ, Country: FINLAND, Abstract-ID: 2158

INTRODUCTION:
Stress causes changes in the functions of the autonomic nervous system as well as in the endocrine and metabolic systems. In military field training, there are often multiple stressors, including physical strain, environmental factors, sleep deprivation, energy deficit, and psychological factors. The main aim of this study was to determine stress factors utilizing heart rate variability, hormone levels, and perceived exertion during three weeks of a military field training. The second aim was to investigate how the changes in the selected subjective and objective measures were related to each other, and whether aerobic fitness and body composition were related to these changes.
METHODS:
A total of 49 men (age 20 ± 1 years; height 179 ± 7 cm; body mass 73.0 ± 8.8 kg) participated in the study. The three-week military training was divided into a shooting training period (5 days), combat training period I (8 days), and combat training period II (7 days). Nocturnal and morning heart rate variability (HRV), anabolic and catabolic hormone status, physical activity, ratio of perceived exertion (RPE), and amount of sleep were investigated before the military field training, periodically during the training, and 4-5 days after the end of the military field training. In addition, aerobic fitness (12-min running test) and body composition were measured.
RESULTS:
During the three-week military field training, nocturnal and morning heart rate, cortisol (COR), RPE, and NASA-Task Load Index (TLX), which assesses the level of stress experienced by an individual while performing a task, increased statistically significantly during the training. Respectively, testosterone (TES) and insulin-like growth factor-1 (IGF-1) levels decreased statistically significantly. Only a few statistically significant changes were observed in the HRV variables. The observed stress, caused by the military field training, seems to recover to its initial levels or close to them within 4-5 days after the end of the training. There were weak associations between the changes in the subjective and objective measures but, however, RPE was associated with TES (r=-0.30, p<0.05) and NASA-TLX with COR (r=0.49, p<0.01).
CONCLUSION:
The stress caused by military field training caused changes in the functions of the autonomic nervous system as well as the endocrine and metabolic systems. The changes indicate that the training increased the participants’ physiological and / or psychological stress, leading the body to a more catabolic state. It was, however, challenging to interpret the results while the changes in the studied variables varied individually. It can be concluded that the present study can provide interesting data about the workload of military field training. In addition, it seems that different measurement methods and tools are needed for obtaining better quality data and thus, improving the reliability and reproducibility of the study. Finally, individual responses and adaptations should be taken into considerati