HEART RATE VARIABILITY FOR EVALUATING COGNITIVE STRESS IN HEALTHY STUDENTS: THE INFLUENCE OF PHYSICAL FITNESS LEVEL

Abstract

Background. The impact of adaptation to physical loads on heart rate variability (HRV) responses during cognitive or emotional stress remains insufficiently studied. This study aimed to examine changes in HRV parameters among individuals with differing levels of adaptation to speed-strength physical loads while performing complex visual-motor reaction (VMR) tasks.
Materials and Methods. The study compared HRV metrics between trained males (22 karate athletes, Group T) and untrained males (26 students, Group UT). Groups did not differ significantly in age and anthropometric parameters. HRV was recorded both at rest and during three complex visual-motor choice reaction (VMCR) tests involving increasing numbers of stimuli – VMCR₆₀, VMCR₉₀, and VMCR₁₂₀. The following HRV indices were calculated: the heart rate (HR), the standard deviation of normal RR intervals (SDNN), the root mean square of successive differences (RMSSD), the percentage of successive interval pairs differing by more than 50 ms (pNN₅₀), the length of the short axis of the Poincaré plot (SD₁), and the length of the long axis of the Poincaré plot (SD₂)
Results and Discussion. At rest, values of SDNN, SD₁, RMSSD, and pNN₅₀ were 11.80–43.01 % higher in group T than in group UT (p < 0.05), while HR was 7.40 % lower in group T (p <0.05). A tendency towards the prevalence of persons with dominance of sympathetic tone within the group UT was observed. During VMCR tasks, HRV parameters changed in both groups. Specifically, SDNN decreased by 38–42 % (p <0.01), with a more pronounced reduction in group T. We found a nearly significant strong negative correlation between SDNN reduction and the number of stimuli in the VMCR tests (r = -0.99, p = 0.10) in group UT. During the VMCR tasks, group T showed significant decreases in RMSSD (p <0.01) and pNN₅₀ (p = 0.03), whereas no significant changes were observed in group UT. A nearly significant strong negative correlation was found between pNN₅₀ and the number of stimuli in group UT (r = -0.99, p = 0.08), in contrast to group T. The SD₁ decreased significantly during the VMCR tasks in both groups (p <0.01), with a nearly significant correlation between these changes and the number of stimuli in group T (r = -0.995, p = 0.06) and group UT (r = -0.992, p = 0.07). The effect of VMCR on SD₁ was more pronounced in group T. Furthermore, SD₂ significantly decreased during VMCR in both groups (p <0.01), with larger reductions observed in group T. Analysis of HRV at rest suggests that adaptation to speed-strength training is associated with an enhanced parasympathetic tone. Under cognitive load, there is a shift toward increased sympathetic activity. These changes are more pronounced and occur more rapidly in trained individuals, as indicated by the progressive alterations in specific HRV parameters among the untrained group during the sequential series of tests.
Conclusion. Individuals adapted to speed-strength training exhibited higher parasympathetic activity at rest and more efficient sympathetic responses to cognitive load, indicating superior autonomic regulation adaptability compared to untrained individuals.