Effect of Moderate Versus High Intensity Interval Exercise Training on Heart Rate Variability Parameters in Inactive Latin-American Adults: A Randomized Clinical Trial

PURPOSE: Decreased heart rate variability (HRV) is associated with a higher risk of mortality and exercise training is effective to its increase in inactive adults. We investigated the effect of moderate versus high intensity interval exercise training on HRV indices in physically inactive adults.

METHODS: Twenty inactive adults were randomly allocated to receive either moderate intensity training (MCT group) or high intensity interval training (HIT group). The MCT group performed aerobic training at an intensity of 55-75% of the walking on a treadmill at 60-80% heart rate max (HRmax) until expenditure of 300 kcal until the end of training. The HIT group performed running on a treadmill during 4 minutes at 85-95% peak HRmax and had a recovery of 4 minutes at 65% peak HRmax until expenditure of 300 kcal until the end of training. Supine resting HRV indices (time domain: SDNN, standard deviation of normal-to-normal intervals ; rMSSD, Root mean square successive difference of RR intervals and frequency domain: HFLn, high frequency spectral power; LF, low frequency spectral power; and HF/LF ratio) and were measured at baseline and 12-weeks thereafter.

RESULTS: SDNN changes were 3.4 (8.9) ms in the MCT group, 29.1 (7.6) ms in the HIT group (difference between groups 32.6 [95% CI, 24.9 to 40.4 (P = 0.01)]. LF/HFLn ratio change in the MCT group 0.19 (0.03) ms and in HIT group 0.13 (0.01) ms (P between groups = 0.016). No significant group differences were observed in rMSSD, HF, and LF parameters. Finally, we observed stronger correlation between Ln rMSSD and to-R-R interval in HIT group (rs = 0.834; p < 0.001) Figure 1A, and not significant correlation between Ln rMSSD and to-R-R interval in MCT group (rs = 0.396; p = 0.290), Figure 1B.

CONCLUSIONS: In inactive adults, this study showed that a 12-week HIT training program can increase short-term HRV, mostly in vagal mediated indices such as SDNN and HF/LFLn ratio power.