Effect of Aging on Heart Rate Variability at Onset of Isolated Post‐Exercise Muscle Metaboreflex Activation in Healthy Adults
Authors: Drew Rachel C. , Sánchez‐Hechavarría Miguel E. , Carrazana‐Escalona Ramón , Blaha Cheryl A. , Sinoway Lawrence I. 
Published: June 2021

Immediately following cessation of exercise, central command and muscle mechanoreflex inputs are removed but muscle metaboreflex input can remain in certain situations. Continuous wavelet transform (CWT) analysis is an approach that allows analysis of heart rate variability (HRV) at times of rapid autonomic nervous system adjustments. Recent preliminary findings have identified the restoration of parasympathetic modulation of HRV and/or reduction in sympathetic modulation of HRV during the onset of isolated post‐exercise muscle metaboreflex activation in healthy young adults. However, whether healthy aging affects these rapid autonomic adjustments at the onset of isolated post‐exercise muscle metaboreflex activation has not been investigated to date. Therefore, we retrospectively applied CWT analysis to data previously collected from 11 healthy older adults (Older; 6 men/5 women; mean ± SD age 62 ± 1y) who performed two trials involving 1.5 minutes of one‐legged, isometric, calf exercise at 70% maximal voluntary contraction (70% trial) or rest (0% trial), followed by circulatory occlusion via cuff inflation around the exercised limb that was maintained for 30 seconds to isolate muscle metaboreflex activation immediately post‐exercise (70% trial) or to act as a control when the limb was rested (0% trial). We also compared the older participants' data to data previously collected from 14 healthy young adults (Young; 8 women/6 men; mean ± SD age 26 ± 2y) who performed the same two trials. CWT analysis of R‐R intervals (electrocardiogram) included log‐transformed absolute and normalized low‐frequency (LF; 0.04–0.15Hz) and high‐frequency (HF; 0.15–0.4Hz) time‐frequency bands and the ratio of LF/HF for a 30‐s baseline period and each of the six 5‐s time windows during the 30‐s isolated muscle metaboreflex activation. Statistical analysis involved three‐way repeated measures analysis of variance with post hoc analysis involving t tests with a Holm‐Bonferroni correction. Normalized HF power was lower and normalized LF power and LF/HF was higher in Older compared to Young (P< 0.05). Further, LF‐HF was higher during the 1–5s and 6–10s time windows (3.32 ± 0.97% and 3.07 ± 0.80%, respectively) compared to the rest, 21–25s, or 26–30s time windows (2.29 ± 0.81%, 1.97 ± 1.00%, and 1.99 ± 0.91%, respectively) in the 70% trial in Young but not Older (P< 0.05). These findings suggest that in healthy older adults, the restoration of parasympathetic modulation of HRV and/or reduction in sympathetic modulation of HRV during the onset of isolated post‐exercise muscle metaboreflex activation is absent. In conclusion, healthy older adults do not exhibit the restoration of parasympathetic modulation of HRV and/or reduction in sympathetic modulation of HRV during the onset of isolated post‐exercise muscle metaboreflex activation that is observed in healthy young adults.Support or Funding InformationSupported by National Institutes of Health grants UL1 TR000127 and P01 HL096570.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.