# Vagal Activity and Fat Oxidation Basal Correlates in Older Active Postmenopausal Women: A Cross-Sectional Study

## TL;DR

This study finds that heart rate variability, specifically Total power, is strongly linked to fat oxidation in older active postmenopausal women.

## Contribution

The study identifies Total power as a stronger predictor of resting fat oxidation than energy expenditure in postmenopausal women.

## Key findings

- Total power is the strongest predictor of resting fat oxidation in postmenopausal women.
- RMSSD and Total power explain 30% of fat oxidation variance when combined with energy expenditure.
- Non-linear HRV variables like DFA do not correlate with fat oxidation under basal conditions.

## Abstract

Heart Rate Variability at rest has been recently associated with metabolic outcomes alongside exercise, which in turn have been associated with energy expenditure, muscle power and fat mass. This study aimed to analyse the relationship at rest between autonomic function and metabolic outcomes, in physically active postmenopausal women. We hypothesised that, autonomic function is more strongly associated with Fat oxidation than basal metabolic rate. In sixty-one active postmenopausal women (67.9 ± 5.3 years; 40.3 ± 4.3 kg muscle mass) basal metabolic rate and Heart Rate Variability analysis was recorded simultaneously for 30 min with participants resting supine under standardised activity and diet conditions.

Root Mean Square of Successive Differences of heart beats (RMSSD) and Total power showed a predictive value for resting Fat oxidation (β = 0.46; β = 0.26), explaining 30% of the variance. Including traditional predictors such as energy expenditure increased explained variance to 57.5%. In this model, RMSSD association disappeared, Total power (β = 0.88) became the strongest predictor, and together with energy expenditure (β = 0.53), showed significant associations with FATox. Respiratory exchange ratio only correlated with RMSSD (β = − 0.54) in the isolated Heart Rate Variability model, without basal metabolic rate associations. Box plots of RMSSD quartiles revealed a difference in fat-oxidation between the highest and lowest quartiles, a pattern not seen for Total power.

Baroreflex activity and fat oxidation associate at rest in active postmenopausal women with preserved cardiovascular function. Total power emerges as the strongest Heart Rate Variability predictor of baseline Fat oxidation in the multivariable models. Stratification by RMSSD quartiles revealed graded differences in fat oxidation rates across levels of vagal modulation.

Clinical Trials, NCT06336070. https://clinicaltrials.gov/study/NCT06336070 Registered: 4 April 2024.

The online version contains supplementary material available at 10.1186/s40798-026-01004-1.

Data reveal a robust association between cardiac vagal activity, measured through RMSSD and Total power, and the rate of Fat oxidation at rest in physically active postmenopausal women. Non-linear variables such as detrended fluctuation analysis (DFA) do not associate under basal conditions.Despite the age-related decline, the postmenopausal active women displayed preserved autonomic and metabolic responses, evidenced by moderate sympathetic index and maintained RMSSD values, low respiratory exchange ratios and high Fat oxidation rates.A combined predictive model further establishes that Total power, indicative of baroreflex sensitivity, more accurately predicts resting Fat oxidation than overall energy expenditure, suggesting that HRV signals may be key markers of metabolic health in this aging population.

Data reveal a robust association between cardiac vagal activity, measured through RMSSD and Total power, and the rate of Fat oxidation at rest in physically active postmenopausal women. Non-linear variables such as detrended fluctuation analysis (DFA) do not associate under basal conditions.

Despite the age-related decline, the postmenopausal active women displayed preserved autonomic and metabolic responses, evidenced by moderate sympathetic index and maintained RMSSD values, low respiratory exchange ratios and high Fat oxidation rates.

A combined predictive model further establishes that Total power, indicative of baroreflex sensitivity, more accurately predicts resting Fat oxidation than overall energy expenditure, suggesting that HRV signals may be key markers of metabolic health in this aging population.

The online version contains supplementary material available at 10.1186/s40798-026-01004-1.