The Influence of an Acute Bout of High-Intensity Interval Exercise on Heart Rate Variability Indices and Stress Index in the Absence of Cardiometabolic Diseases

Introduction: The maximal rate of oxygen consumption is the gold standard when determining cardiorespiratory fitness (CF) in healthy and diseased populations. CF has been shown to influence the improvement of cardiac autonomic modulation (CAM) and lower the risk of morbidity and mortality rates. High-intensity interval exercise (HIIE) has been shown to influence CAM post-exercise in various populations. Heart rate variability (HRV) is a non-invasive way to assess CAM during, before, and after exercise. The purpose was to determine if a single acute bout of HIIE is influenced by age and CF when correlated to HRV variables to determine CAM in healthy and fit individuals. Methods: Thirty-four healthy individuals (n= 21 male; n = 13 female) completed a single acute bout of HIIE session to quantify CAM via HRV. HRV was assessed pre, 1-hour, and 24-hours post-exercise using time and frequency domains, and stress index (SI). Results: HRV time and frequency domains were not significantly changed. The SI was significantly different between pre, 1-hour, and 24-hours post-exercise (p = 0.001). The SI was also significantly different between age groups (p = 0.025). Conclusion: The lack of significant difference in CAM can be attributed to the participants high CF, which helps maintain their HRV as they age. Additionally, the SI appears to be a good metric to assess CF as individuals age.