Sex-related differences in heart rate variability and static body stability in military personnel under stressful conditions

Abstract

The study focused on examining sex-related differences in the functioning of the autonomic nervous system and static balance performance in operational-level military personnel under stressful conditions. A total of 63 participants were involved, including 33 men (mean age 33.6 ± 1.8 years) and 30 women (mean age 33.1 ± 2.2 years). The objective was to identify and characterize sex differences in the autonomic nervous system’s response to stress and muscle tone in military personnel. Methods: A systematic review of scientific publications performed, using heart rate variability analysis, computerized stabilography, and nonparametric statistical techniques. Results: The HRV analysis revealed statistically significant differences (p ≤ 0.05) between men and women. It was found that 66.7 % of men and 63.3 % of women exhibited a high stress index, significantly exceeding physiological norms. Additionally, the median stress index value for women was statistically significantly higher (p < 0.05). A comparative analysis of spectral variability parameters revealed notable sex differences. Men showed higher overall power (p < 0.01), greater power in the low-frequency ranges, and an increased mean interval between heartbeats (p < 0.05). The analysis of the stress index revealed that 36.4% of servicemen had a low level of stress, while among servicewomen this figure was much lower and amounted to only 23.3 %. Women were more likely to demonstrate high (43.4 %) and moderate levels of stress (23.3 %). Despite the fact that women showed higher levels of stress index based on HRV, there was a paradoxical tendency for women to perform better in static balance tests and no negative impact on coordination abilities. Our results indicate a potential sex specificity of stress response, which is manifested in the ability of women to more effectively compensate for the physiological effects of stress through neuroplastic and other adaptive mechanisms. This is confirmed by statistically significant differences (p < 0.05; p < 0.01) in several parameters, such as COP length, mean velocity of the COP, sway angle variation, and 95 % confidence ellipse area. Women also demonstrated better stability in maintaining a static body position, as evidenced by a decreased COP length. Although not all parameters showed statistically significant differences, the general trend indicates a higher quality of balance function in women, in particular, more adequate compensation for balance disturbances. Conclusion. It was found that men and women demonstrate different physiological responses to stress that are evidenced from the HRV parameters and static balance performance.