Key result
Short-interval HIIT and MICT improve autonomic recovery and HRV over long-interval HIIT.
Why the study?
The study was conducted to compare heart rate dynamics and variability before and after high-intensity interval training and moderate-intensity continuous training protocols based on workload at maximal oxygen uptake.
Does high-intensity interval training alter heart rate dynamics and autonomic cardiac modulation compared to moderate-intensity continuous training in healthy young men?
RCT (n=10)
Randomized crossover design
No
Does high-intensity interval training alter heart rate dynamics and autonomic cardiac modulation compared to moderate-intensity continuous training in healthy young men?
p-value: p=<0.005
HIIT with longer intervals (4 min) induces greater sympathetic hyperactivity and cardiac stress than shorter intervals (30 s) or continuous moderate training, suggesting shorter intervals may be safer for autonomic modulation.
Longer-interval HIIT may heighten post-exercise autonomic stress; extends evidence that interval duration modulates recovery in young men.
The aim of this study was to compare the heart rate (HR) dynamics and variability before and after high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) protocols with workloads based on treadmill workload at which maximal oxygen uptake was achieved ( WL V ˙ O 2 max ) . Ten participants performed cardiopulmonary exercise testing (CPET) to obtain oxygen uptake ( WL V ˙ O 2 max ) . All training protocols were performed on a treadmill, with 0% grade, and had similar total distance. The MICT was composed by 21 min at 70% of WL V ˙ O 2 max . The first HIIT protocol (HIIT-30 : 30) was composed by 29 repetitions of 30 s at 100% of s V ˙ O 2 max and the second HIIT protocol (HIIT-4 : 3) was composed by three repetitions of 4 min at 90% of WL V ˙ O 2 max . Before, during and after each training protocol, HR dynamics and variability (HRV) were analysed by standard kinetics and linear (time and frequency domains). The repeated measures analysis of variance indicated that the HR dynamics, which characterizes the speed of HR during the rest to exercise transition, was statistically ( p < 0.05) slower during MICT in comparison to both HIIT protocols. The HRV analysis, which characterizes the cardiac autonomic modulation during the exercise recovery, was statistically higher in HIIT-4 : 3 in comparison to MICT and HIIT-30 : 30 protocols ( p < 0.005 and p = 0.012, respectively), suggesting that the HIIT-4 : 3 induced higher sympathetic and lower parasympathetic modulation during exercise in comparison to the other training protocols. In conclusion, HIIT-4 : 3 demonstrated post-exercise sympathetic hyperactivity and a higher HRpeak, while the HIIT-30 : 30 and MICT resulted in better HRV and HR in the exercise-recovery transition. The cardiac autonomic balance increased in HIIT-30 : 30 while HIIT-4 : 3 induced sympathetic hyperactivity and cardiac overload.
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Silva et al. (2019) conducted an RCT in Healthy young male individuals (n=10). High-intensity interval training (HIIT) vs. Moderate-intensity continuous training (MICT, 21 min at 70% WL VO2max) was evaluated on Heart rate variability (LF and HF) during exercise recovery (p=<0.005). HIIT-4:3 demonstrated post-exercise sympathetic hyperactivity and a higher HRpeak, while HIIT-30:30 and MICT resulted in better heart rate variability and heart rate recovery.
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