The new approach to calculation of physiological cost of activity: antinociception and normalization of the respiratory pattern of heart rate variability

Purpose of this work is to propose an approach to the assessment of allostatic load based on the antinociceptive effect, which appears, obviously, due to changes in the activity of the endogenous opioid system (EOS); to compare the estimates obtained by measuring the pain threshold and calculating the index of respiratory effects on heart rate variability (HRV). The method of measuring the pain threshold is based on fixing the latent time of the thermonociceptive reaction (LTTR). The respiratory effect is measured by graphically determining the minimum normalized power of the fast HRV component in the range of 0.16... 0.67 Hz, corresponding to the frequency of the respiratory pattern. Results. Based on small-volume experimental data (4 athletes and 4 episodes of physical activity), a quadratic two-factor regression equation was calculated for LTTR, respiratory effects factor and stress. A high correlation was demonstrated between the respiratory effect on HRV and the LTTR for one studied athlete. Conclusion. Using the example of sports, it is shown that it is possible to track the physiological cost of activities through LTTR. The inconveniences and subjectivity of the LTTR measurement procedure can be circumvented by replacing it with a normalized numerical index that considers the effect of breathing on HRV and the stress index. The proposed approach demonstrates the presence of reference values in the studied group, but requires further specially planned clinical studies.