Statistical Analysis on Heart Rate Variability for Graded Cardiopulmonary Groups with Different Exercise Intensities

Abstract

Physical fitness indicates favorable statuses of well-being and health and, more specifically, the ability to perform sports and daily activities. In the paper, we studied heart rate variability with electrocardiogram (ECG) signals under levels of exercise intensities for subjects with different grades of cardiopulmonary fitness. Based on the targeted maximum heart rate, three graded upright biking exercise levels were defined for the experiment: light, moderate, and vigorous. ECG signals were accessed under the rest, at three exercise intensity levels, and in their retrieval periods subsequently. The subjects were in the top 20%, middle, and bottom 20% groups of cardiopulmonary fitness norms from university freshman. Firstly, the major of heart rate variability (HRV) indices performed by spectral and time-domain analyses from collected ECG signals were explored. Statistical analysis was then conducted to identify physiological signal indices with significant differences. All appeared significant differences between the three groups in the frequency domain HRV indices, including high-frequency power (HF), total power (TP), normalized high-frequency power (nHF), normalized low-frequency power (nLF), and LF/HF. The time domain HRV parameters, meanwhile, did not exhibit significant differences among the three groups throughout the graded exercises and in the recover periods. A multiple comparison test on the TP indicated significant differences in most between-group comparisons (except for between groups middle and bottom during moderate exercise, top and middle during recovery from moderate exercise, and middle and bottom during recovery from vigorous exercise). Significant differences were found in most between-group comparisons (except for between groups middle and bottom at rest and during recovery from light and medium exercise and between top and middle during recovery from vigorous exercise).