Rapid adjustments to autonomic control of cardiac rhythm at the onset of isometric exercise in healthy young adults.
Level 3 - non-randomized controlled study
Controlled laboratory crossover physiological study with retrospective signal analysis
PubMed 36823959 · doi:10.14814/phy2.15616
What was done
Retrospective continuous wavelet transform (CWT) time-frequency heart rate variability (HRV) analysis was applied to electrocardiogram R-R interval data from 14 healthy young adults (age 26 ± 2 years). Participants performed a 30-second, one-legged isometric calf contraction at 70% maximal voluntary contraction (MVC) and a resting control condition (0% MVC). Absolute and normalized low-frequency (aLF, nLF; 0.04–0.15 Hz) and high-frequency (aHF, nHF; 0.15–0.4 Hz) spectral bands and the LF/HF ratio were evaluated across a 30-second baseline and six consecutive 5-second windows during the 30-second intervention.
What was found
All HRV metrics (aHF, aLF, LF/HF, nHF, and nLF) demonstrated a significant trial-by-time interaction (all p ≤ 0.027). Compared to the 0% MVC trial, the 70% MVC trial resulted in: - Lower aHF and nHF after 5–30 s (all p ≤ 0.040) - Higher LF/HF and nLF after 5–20 s (all p ≤ 0.045) - Lower aLF after 20–30 s (all p ≤ 0.011) Numerical point estimates and variances were not reported in the abstract.
Why it matters
The findings demonstrate that parasympathetic withdrawal begins earlier (within 5 seconds) than sympathetic activation during the rapid autonomic adjustment to isometric exercise in healthy young adults.
Limits
The study is limited by a small sample size (n = 14) restricted entirely to young, healthy individuals. It relies on a retrospective re-analysis of previously collected single-limb exercise data without reporting absolute point estimates, variance, or direct neural/hemodynamic measurements in the abstract.
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