BACKGROUNDOver one million soldiers were treated for battle- or training-fatigue during World War II. Of all ground combat troops, 37% were discharged for psychiatric reasons due to fatigue. The neuroendocrinological and immunological systems played important roles in the work-related fatigue of military personnel. The aim of this study was to investigate the characteristics of fatigue associated with military operations, and we observed changes in the regulatory functions of the neuroendocrinological and immunological systems that may provide theoretical support for improving the combat effectiveness of armies.

METHODSA total of 240 soldiers from the Field Artillery regiment were selected as subjects. Researchers and subjects received training before participating in the study. Data of the subjects' medical histories, physical examinations, scores on a fatigue assessment scale, and assessments of pituitary-adrenal hormones (adrenal cortical hormone (ACTH), cortical hormone (F), and 24-hour urine-free cortisol (UFC)), pituitary-gonadal hormones (luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone, estradiol (E2), and prolactin (PRL)), pituitary-thyroid hormones (thyroid-stimulating hormone (TSH), thyroxine (TT4), triiodothyronine (TT3), free thyroxine (FT4), and free triiodothyronine (FT3)), and cellular immune parameters (CD3(+), CD4(+), CD8(+), CD4(+)/CD8(+), B, and NK cells) were investigated before and after large-scale and high-intensity field exercises. Data were statistically analyzed with Student's t test using SPSS software (version 13.0), and P values < 0.05 were deemed to be significant.

RESULTSAfter the high-intensity military training, the scores on the fatigue scale reflected significant increases of feeling of unpleasantness among soldiers. Additionally, the symptom checklist showed notable increases in somatization scores and significant decreases in psychoticism scores. After intensive military work, levels of plasma ACTH, F, and UFC of soldiers were decreased (P < 0.01). The level of testosterone decreased significantly after the maneuver ((23.51 ± 6.49) versus (18.89 ± 5.89) nmol/L; P < 0.001), whereas the thyroid function (TT3, FT4, and FT3) was markedly increased after the maneuver (P < 0.01). The number of CD3(+), CD4(+), CD4(+)/CD8(+) cells, and B lymphocytes were decreased (P < 0.05), and NK cells were increased (P < 0.001) after the maneuver.

CONCLUSIONSFollowing high-intensity military operations, the psychological tolerance of soldiers was depressed. And the hypoadrenocorticism (the functional decreases of hypothalamic-pituitary-gonadal and abnormal pituitary-thyroid axis) contributed to the increased levels of fatigue. Hypoimmunity may increase the susceptibility to diseases after high-intensity military operations.