Author(s): NYKANEN, T., OJANEN, T., KYRÖLÄINEN, H., Institution: FINNISH DEFENCE FORCES, Country: FINLAND, Abstract-ID: 2273

INTRODUCTION:
In addition to a well-documented role in neurodegenerative diseases, brain-derived neurotropic factor (BDNF) has also been studied in military environments, where mental stress, energy and sleep deficit, and prolonged physical activity are continuous and fluctuating stress factors (Beckner et al. 2022). Reduction in body mass and remarkable hormonal responses are often observed simultaneously in this type of trainings (Ojanen et al. 2023). BDNF concentration typically decreases in strenuous environments, but the function of this neurotrophin is not clearly understood. Thus, the purpose of this study was to a) describe BDNF responses in multi-stress military training, b) examine associations between BDNF, body composition and biomarkers, and c) study the effect of 36 hours’ recovery on these outcomes during training.
METHODS:
Two groups of male soldiers were studied: FEX (n=42, 19.5 ± 0.8 years, 179 ± 6 cm, 74.4 ± 10.8 kg) had continuous winter field training with energy and sleep deficit, while REC (n=26, 19.7 ± 1.2, 181 ± 6 cm, 78,2 ± 9.6 kg) had 36-hours active recovery phase in the middle of training (days 6 to 8). Body composition was measured via bioimpedance, and blood samples for BDNF and biomarkers (testosterone, cortisol, IGF-1, leptin, ghrelin, adrenalin, noradrenalin, prolactin, sex hormone binding protein) were collected at days 1, 6, 8, 10 during training. Linear mixed model was used for evaluating main effects and interactions between time and group, and Spearman correlations with FDR adjustments for associations between BDNF, body composition and biomarkers. Statistical significance was set as p<0.05.
RESULTS:
BDNF decreased in both groups during training and systematically lower BDNF values were found in the REC group compared to the FEX group (main effects with time p<0.001 and group p=0.011). No associations were found between BDNF, body composition or metabolic biomarkers at any time points, and further, changes in BDNF concentration did not associate with changes in body composition or biomarkers.
CONCLUSION:
A decrease in BDNF levels was found during multi-stress military training in both groups, regardless of the active recovery period of the REC group. Higher initial body mass was observed in the REC group, but none of the body composition variables, or biomarkers, explained the systematic difference in BDNF levels observed in this data. Further research is needed to elucidate the role of BDNF in anabolic and catabolic processes in multi-stress military environments.

Beckner ME, Main L, Tait JL, Martin BJ, Conkright WR, Nindl BC. 2022. Circulating biomarkers associated with performance and resilience during military operational stress. Eur J Sport Sci. 22(1):72-86.
Ojanen, T., Pihlainen, K., Yli-Renko, J., Vaara, J., Nykänen, T., Heikkinen, R. & Kyröläinen, H. (2023). Effects of 36-hour recovery on marksmanship and hormone concentrations during strenuous winter military survival training. BMC Sports Science, Medicine and Rehabilitation, 15(1).