Sex differences and acute intermittent isometric handgrip exercise effects on microvascular reactivity in young healthy adults.
- 1Applied Physiology Laboratory, Department of Kinesiology, Health Promotion and Recreation, School of Health Sciences, College of Health and Public Service, University of North Texas, Denton, TX, United States.
Abstract
Introduction
Near-infrared spectroscopy combined with a vascular occlusion test (NIRS-VOT) is a popular approach for investigating microvascular function across many settings. Although sex differences and exercise-induced changes in NIRS-VOT responses have been reported, limited evidence exists detailing whether these responses persist after accounting for confounding factors such as adipose tissue thickness (ATT) and the magnitude of the ischemic stimulus. Therefore, the purpose of this study was twofold: 1) to determine whether sex explains variability in NIRS-VOT outcomes beyond that accounted for by ATT and measures of the ischemic stimulus, and 2) to determine the extent to which acute isometric handgrip exercise influences NIRS-VOT responses in a sex-specific manner.Methods
Twenty-four healthy adults (12 males) completed two experimental visits consisting of repeated NIRS-VOTs performed before and after either rhythmic handgrip exercise (30 contractions at 50% maximal voluntary contraction) or time-matched rest. Ischemia was terminated once 40% skeletal muscle tissue oxygenation (StO₂) was observed to standardize the ischemic stimulus. Model comparison analyses evaluated the predictive contributions of sex, ATT, and cumulative O₂ deficit to upslope, maximal saturation (StO2max), and half-time to StO2max (T1/2). Linear mixed-effects models examined the effects of Sex, Condition, and Time on NIRS-VOT outcomes.Results
Sex was the strongest predictor of upslope, explaining approximately 15% of the variance, whereas cumulative O₂ deficit was the strongest predictor of StO2max and T1/2. Acute exercise increased downslope and upslope while reducing StO2max (all p < 0.05). However, no Sex × Condition × Time interactions were detected (all p > 0.05). Because the study was not powered to detect higher-order interactions, the sex-specific exercise analyses should be considered exploratory rather than evidence that males and females respond equivalently.Discussion
Overall, these results demonstrate that determinants of NIRS-VOT responses are outcome-specific and influenced by both skeletal muscle metabolic characteristics and microvascular function. Cumulative O₂ deficit emerged as a primary determinant of StO2max, supporting a muscle-centric framework for interpreting at least some NIRS-derived measures of reactive hyperemia.
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BibTeX
@article{lee2026differences,
title = {{Sex differences and acute intermittent isometric handgrip exercise effects on microvascular reactivity in young healthy adults.}},
author = {Wonjae Lee and Elizabeth G Knoll and Kase J Pennartz and Justin D Sprick and Joshua L Keller},
journal = {Frontiers in physiology},
year = {2026},
month = oct,
doi = {10.3389/fphys.2026.1895045},
url = {https://europepmc.org/article/MED/42947995},
note = {CC BY},
}
RIS
TY - JOUR
TI - Sex differences and acute intermittent isometric handgrip exercise effects on microvascular reactivity in young healthy adults.
AU - Wonjae Lee
AU - Elizabeth G Knoll
AU - Kase J Pennartz
AU - Justin D Sprick
AU - Joshua L Keller
PY - 2026
DA - 2026/10/13
JO - Frontiers in physiology
DO - 10.3389/fphys.2026.1895045
UR - https://europepmc.org/article/MED/42947995
AB - Introduction Near-infrared spectroscopy combined with a vascular occlusion test (NIRS-VOT) is a popular approach for investigating microvascular function across many settings. Although sex differences and exercise-induced changes in NIRS-VOT responses have been reported, limited evidence exists detailing whether these responses persist after accounting for confounding factors such as adipose tissue thickness (ATT) and the magnitude of the ischemic stimulus. Therefore, the purpose of this study was twofold: 1) to determine whether sex explains variability in NIRS-VOT outcomes beyond that accounted for by ATT and measures of the ischemic stimulus, and 2) to determine the extent to which acute isometric handgrip exercise influences NIRS-VOT responses in a sex-specific manner.Methods Twenty-four healthy adults (12 males) completed two experimental visits consisting of repeated NIRS-VOTs performed before and after either rhythmic handgrip exercise (30 contractions at 50% maximal voluntary contraction) or time-matched rest. Ischemia was terminated once 40% skeletal muscle tissue oxygenation (StO₂) was observed to standardize the ischemic stimulus. Model comparison analyses evaluated the predictive contributions of sex, ATT, and cumulative O₂ deficit to upslope, maximal saturation (StO2max), and half-time to StO2max (T1/2). Linear mixed-effects models examined the effects of Sex, Condition, and Time on NIRS-VOT outcomes.Results Sex was the strongest predictor of upslope, explaining approximately 15% of the variance, whereas cumulative O₂ deficit was the strongest predictor of StO2max and T1/2. Acute exercise increased downslope and upslope while reducing StO2max (all p < 0.05). However, no Sex × Condition × Time interactions were detected (all p > 0.05). Because the study was not powered to detect higher-order interactions, the sex-specific exercise analyses should be considered exploratory rather than evidence that males and females respond equivalently.Discussion Overall, these results demonstrate that determinants of NIRS-VOT responses are outcome-specific and influenced by both skeletal muscle metabolic characteristics and microvascular function. Cumulative O₂ deficit emerged as a primary determinant of StO2max, supporting a muscle-centric framework for interpreting at least some NIRS-derived measures of reactive hyperemia.
SN - 1664-042X
ER -