An optimization study of the ultra-short period for HRV analysis at rest and post-exercise

Background: Ultra-short-termheart rate variability (HRV) analysis (< 5 min) has been extensively growing in the field of exercise performance for autonomic assessment. However, the validation of ultra-short-term HRV was unclear in the recovery period of exercise. This study aimed to elucidate the agreement between ultra-short-term HRV (0-30 s, 0-1 min, 0-2 min, 0-3 min, 0-4 min) and standard short-term HRV (5 min) and to explore the optimal recording duration under rest and post-exercise conditions. Methods: 69 participants were recruited to perform physical exercise on a treadmill with an intensity of 6 km/h, 9 km/h and 12 km/h, independently. The standard deviation of RR-interval (SDNN) and rootmean square of successive differences of RR-intervals (RMSSD) were calculated by using ultra-short periods and standard period at rest condition (Pre-E) and three post-exercise trials, i.e., Post-E1, Post-E2 and Post-E3, respectively. One-way ANOVA with repeated-measures and Cohen's d statistics were conducted, and Bland-Altman analysis and interclass correlation coefficients (ICC) were used to assess the levels of agreement. Results: For SDNN and RMSSD, the results of agreement analysis at rest condition were different from those at post-exercise. At Pre-E, SDNN and RMSSD were reliable for ultra-short-term HRV analysis at all ultra-short periods, i.e., 0-30 s, 0-1 min, 0-2 min, 0-3 min and 0-4 min, with most ICCs greater than 0.9 and Cohen's d showing trivial differences (Cohen's d = 0.024-0.117). However, at post-exercise, SDNN0-30s, SDNN0-1min, RMSSD0-30s and RMSSD0-1min showed significant differences with SDNN5min and RMSSD5min, respectively (p < 0.01), and the ICCs was not perfect (< 0.9). HRV analysis with time duration longer than 2 min showed nearly perfect reliability in all post-exercise trials, with trivial differences (Cohen's d = -0.003-0.110) and perfect ICCs (ICCs = 0.916-0.998). Furthermore, the limits of the agreement became tighter as the period duration increased in Bland-Altman plots. Conclusions: This study demonstrated that ultra-short-term HRV analysis was a good surrogate of standard HRV time-domain measures to reflect the autonomic regulation at rest and post-exercise. Specifically, ultra-short-term HRV0-30s or HRV0-1min was recommended at rest condition, whereas longer than 2 min recording period was reliable to obtain SDNN and RMSSD for the accuracy of HRV analysis. (C) 2020 Published by Elsevier Inc.