Comparison of Heart Rate Variability After Constant and High Intensity Interval Training Exercise Sessions

Abstract

Although regular physical activity improves autonomic function, including heart rate variability (HRV), the risk of sudden death is increased immediately after exercise, possibly related to acute changes in autonomic tone. The high intensity interval training (HIIT) improves aerobic capacity and performance, however, the short-term effects of a single bout of HIIT on HRV was unclear. PURPOSE: To evaluate and compare the short-term HRV after a single bout of constant and HIIT exercises. METHODS: Eighteen healthy men (26.6 ± 4.8 yr; body fat 17.3 ± 4.6%; VO2max 52.2 ± 5.8 ml/kg/min) performed an incremental test to determine the VO2max and running speed at VO2max (vVO2max). After 48 h, the participants performed randomly and separated by 48 h two single bouts of (i) 30 min of constant exercise at 70 – 75% of VO2max and (ii) HIIT consisting of 10 runs at vVO2max of 1 min separated by 1 min passive recovery periods. The HRV was recorded before and between 0-10, 25-35 and 50-60 min after the sessions and analyzed by spectral analysis (normalized low (LF) and high (HF) frequency and LF/HF ratio) and time domain parameters (interval RR (iRR), SDNN, rMSSD and pNN50). RESULTS: There were no differences (p>0,05) in HRV at rest between sessions (constant session: iRR 915.8 ± 118.4 ms; SDNN 55.5 ± 15.9 ms; rMSSD 52.9 ± 23.1 ms; pNN50 28.1 ± 17.1%; LF 63.2 ± 16.1; HF 36.7 ± 16.1; LF/HF 2.34 ± 1.64 and HIIT session: iRR 897.2 ± 121.8 ms; SDNN 54.1 ± 19.9 ms; rMSSD 50.3 ± 25.2 ms; pNN50 25.9 ± 18.3%; LF 67.1 ± 12.2; HF 32.8 ± 12.2; LF/HF 2.72 ± 2.14). During the recovery period, the iRR, SDNN, rMSSD, pNN50 and HF values were lower (p<0.05) and the LF and LF/HF ratio values were higher (p<0.05) than the resting period. Between 0-10, 25-35 and 50-60 min, the time domain parameters presented a recovery (p<0.05) for the two sessions; however, pNN50 was higher for constant exercise at 50-60 min (14.3 ± 16.9% for constant exercise and 9.4 ± 10.1% for HIIT). For the spectral analysis parameters, the recovery (p<0.05) was also noted between 0-10, 25-35 and 50-60 min but only for the constant exercise. LF, HF and LF/HF ratio showed no difference (p>0.05) between 25-35 and 50-60 min for the HIIT session, indicating a slow recovery. CONCLUSION: The short-term HRV recovery seemed depended on the type of exercise. The depressed parasympathetic and enhanced sympathetic activity observed during 1 h after exercise seems to be greater after HIIT exercise.