Abstract
PURPOSE: The natural log transformation of the root mean square of successive R-R differences (lnRMSSD) is a parasympathetic measure of heart rate variability. The extent to the relationship between lnRMSSD and localized muscle damage following exercise is unknown..The purpose of this study was to examine the relationship between lnRMSSD and Rectus femoris CSA (CSA-RF) following an exhaustive bout of exercise over 72 hours. METHODS: Twelve participants were measured for pre-exercise lnRMSSD for five minutes in a seated position, followed by a CSA-RF measurement with musculoskeletal ultrasound 15 cm above the superior pole of the participant’s right patella. Next participants completed an exhaustive exercise protocol. Finally, participants repeated the lnRMSSD and CSA-RF measures immediately following exercise termination with follow-up testing at 24-hours, 48-hours, and 72-hours. RESULTS: Repeated measures ANOVA revealed significant differences in lnRMSSD between pre-exercise and post-exercise measures (p = .002, Table 1), but no other significant differences. Likewise, there were significant differences in CSA-RF from pre-exercise to post-exercise (p < .001, Table 1), but no other differences were noted. There was a large near-significant correlation between the changes in lnRMSSD and CSA-RF from pre-exercise to post-exercise (r = -.57, p = .055), and large statistically significant correlation between the changes in lnRMSSD and CSA-RF from pre-exercise measures to 24-hour follow-up (r = -.64, p = .025). CONCLUSIONS: In this study lnRMSSD declined as CSA-RF increased immediately following exercise up to 24 hours. This inverse relationship is likely the result of vagal tone suppression and increased sympathetic outflow in cardiac control during and immediately following exercise. Tracking lnRMSSD following exercise may give practitioners further insight to the mechanisms of recovery.Table: No title available.
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