Monitoring the Effects of Resistance Exercise on Heart Rate Variability
Heart rate variability (HRV) has become a popular tool for monitoring autonomic stress responses, however, the efficacy of HRV as a valid internal training load marker for resistance exercise has not been well-established. We conducted three studies to address this gap. Study 1 compared the effects of low, moderate, and high set volumes in acute resistance exercise sessions on post-exercise parasympathetic reactivation. Three full-body resistance exercise sessions of varying set volumes were performed with HRV being measured pre- and for 30 minutes post-exercise. Statistically significant differences were observed across sessions and recording times (p?.05), but not with the session Ã— time interaction. When comparing pre-post exercise HRV, significant differences were found across all sessions. The low volume session was significantly different from both the moderate and high volume sessions, but no differences were found between moderate and high volume sessions. Study 2 determined the relationship between pre-post changes in HRV, neuromuscular performance, and biochemical fatigue markers in response to resistance exercise. A bout of high set volume resistance exercise was performed with HRV, neuromuscular performance, and biochemical fatigue markers being measured pre- and post-exercise. Statistically significant correlations were observed with ?HRV Post5-10 and ?Lactate immediate post-exercise (r = -0.440, p = .036), and ?HRV Post5-10 and ?Lactate Post30 (r = -0.549, p <.001). Study 3 examined the validity and reliability of HRV derived from smartphone photoplethysmography (PPG) under resting and post-resistance exercise conditions. Participants completed four resting, simultaneous ECG and PPG measurements on separate days and one measure post-resistance exercise. Significant, yet small (ES=0.2-0.6) to moderate (ES=1.14) differences were found between simultaneous measures with moderate-to-very large correlations (r=0.41-0.76) and good agreement at rest. For the intraday reliability of PPG, ICC was “nearly perfect” (ICC=0.91) and interday reliability ICC was “very large” (ICC=0.88). The use of smartphone PPG seems to be an appropriate surrogate for ECG. However, HRV may not be a sensitive enough method for detecting all differences in set volumes. Practitioners should use an integrative approach to assess an individual’s recovery status and readiness to perform.