The Effects Of High Intensity Interval Training On Heart Rate Variability In Physically Inactive Adults

Abstract

High intensity interval training (HIIT) is a type of exercise that involves repeated intense exercise with active or passive recovery. Heart rate variability (HRV) analysis has been widely used to measure cardio-autonomic functions. PURPOSE: The purpose of this study was to examine the effects of HIIT on heart rate variability (HRV) in physically inactive adults. METHODS: This study was conducted with a randomized and controlled design. Thirteen physically inactive male adults (27.5 ± 3.80 years) were randomly assigned to HIIT (N = 7) or moderate intensity continuous training (MICT, N = 6). The HIIT program consisted of 20 min of interval training with work to rest ratio (10/50 sec) at 90% HRpeak while the MICT program consisted of 40 min of continuous training at 60-75% HRpeak. Both groups completed 8 sessions of cycle training over a period of two weeks. Height, body weight, blood pressure, and body composition were measured. HRV was measured for 20 minutes in sitting position with Actiwave-Cardio (CamNtech, UK). Time domain (R-R interval, IBI, RMSSD) and frequency domain (high frequency, low frequency, and LF/HF ratio) variables were analyzed by actiwave analyzer. A natural logarithmic transformation of all frequency domain variables was performed to meet the assumptions of parametric statistical analysis. Rrepeated measures ANOVAs were applied to analyze interaction effects on HRV variables and the significant level was set at .05. RESULTS: Significant time effects on R-R interval (F = 8.437, p < 0.05) and IBI (F = 9.611, p < 0.05) were observed with both HIIT and MICT groups decreasing over time. lnLF/HF ratio was significantly decreased in the HIIT group while the MICT group did not change (F = 4.875, p < 0.05). CONCLUSIONS: The present study suggests that the HIIT program improves sympathovagal (lnLF/HF ratio) activity following only 8 sessions of HIIT. Health professionals or fitness trainers could consider this time efficient exercise program (HIIT) for improving cardio-autonomic function in adults who are physically inactive.