Reliability of heart rate measures used to assess post-exercise parasympathetic reactivation

Postexercise HRR (heart rate recovery) and HRV (heart rate variability) are commonly used to asses non-invasive cardiac autonomic regulation and more particularly reactivation parasympathetic function. Unfortunately, the reliability of postexercise HRR and HRV remains poorly quantified and is still lacking. The aim of this study was to examine absolute and relative reliability of HRR and HRV indices used to assess postexercise cardiac parasympathetic reactivation.

We studied 30 healthy men, who underwent 10-minute heart rate recording after cessation of maximal and submaximal intensity exercises. Each condition of testing was repeated twice within 5 ± 2 days after the first one. Standard indexes of HRR and HRV were computed from heart rate and RR intervals.

We found no significant bias between repeated measures. Relative reliability was assessed with the intraclass coefficient correlation (ICC) and absolute reliability with the standard error measurement (SEM) and coefficient of variation (CV). A large range for ICC was observed for both indexes of HRR and HRV (0.12

According to our results, ∆60 (the absolute difference between heart rate immediately at the end of exercise and after 60 s) and HFnu (High Frequency expressed in normalized unit; that is, in a percentage of LF+HF) represent the most reliable parameters. In conclusion, we found that the measures used to asses cardiac parasympathetic reactivation were characterized by large random variations and their reliability remains moderate.