Rapid Adjustments to Autonomic Control of Cardiac Rhythm at the Onset of Isometric Exercise in Healthy Young Adults
Date of Award
Campus Access Thesis
Master of Science (MS)
Exercise and Health Science
Rachel C. Drew
Sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) activities change during exercise, which can be reflected in time- and frequency-based heart rate variability (HRV) analysis. Continuous wavelet transform (CWT) allows analysis of HRV at times of rapid autonomic adjustments. However, the SNS and PNS contributions to cardiac rhythm at the onset of exercise, a time of rapid autonomic adjustments, is a clinically important area of investigation that has yet been addressed due to the complexity of applying HRV analysis during short durations of exercise. The purpose of this study was to characterize the SNS and PNS influences on cardiac rhythm using CWT HRV analysis at the onset of isometric exercise in healthy young adults. CWT analysis was retrospectively applied to data previously collected from 14 healthy young adults (26 ± 2 years, 6 male/8 female) who performed one-legged, isometric, right-calf exercise at 70% maximal voluntary contraction (MVC) for 30 seconds (70% MVC) or continued to rest (0% MVC). CWT analysis of R-R intervals (RRI, electrocardiogram) included log-transformed absolute and normalized low-frequency (aLF and nLF; 0.04-0.15 Hz) and high-frequency (aHF and nHF; 0.15-0.4 Hz) frequency bands and the ratio of LF/HF for a 30-s baseline period and each of the six 5-s time windows for 0% and 70% MVC trials. Statistical analysis involved two-way repeated measures analysis of variance with post-hoc analysis involving paired t-tests and a Holm-Bonferroni correction with statistical significance set at P < 0.05. There was a significant trial-time interaction for aHF, aLF, and LF/HF (P < 0.001, P = 0.003, and P = 0.027, respectively). Following the start of exercise in the 70% MVC trial compared to the 0% trial, aHF was lower after 5-30 seconds (all P ≤ 0.025), aLF was lower after 20-30 seconds (all P ≤ 0.011), and LF/HF was higher after 5-20 seconds (all P ≤ 0.045). These results indicate that the reduction of the PNS influence on cardiac rhythm begins sooner than the augmentation of the SNS influence on cardiac rhythm at the onset of exercise in healthy young adults.
Oliver, Tyler E., "Rapid Adjustments to Autonomic Control of Cardiac Rhythm at the Onset of Isometric Exercise in Healthy Young Adults" (2022). Graduate Masters Theses. 745.
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