Honors Theses

Date of Award

5-2025

Document Type

Undergraduate Thesis

Degree Name

BS

Department

Chemistry

Faculty Mentor

Joshua L. Keller

Advisor(s)

Jason Coym, Ryan Colquhoun

Abstract

Purpose: Handgrip (HG) strength is a potent predictor of cardiovascular disease (CVD) and all-cause mortality. Advances in technology have provided novel assessments of peripheral microvascular health and function such as measurements of skeletal muscle tissue oxygenation (StO2, %) with near-infrared spectroscopy (NIRS) during vascular occlusion tests (VOT). Although NIRS-VOT derived measures have been shown to change across the lifespan, it is unknown if these variables are sensitive to group differences as defined by HG strength. Therefore, our purpose was to examine mean differences in NIRS-VOT parameters across the lifespan and between groups of low and high HG strength. We hypothesized that individuals with lower HG strength would exhibit lower vascular function, and that older individuals would have slower vascular responses. Methods: 84 adults were separated into age groups: 29 young (19 – 40 yr), 28 midlife (41 – 64 yr), and 27 older (65+ yr). Groups were divided into low and high strength at the median for HG strength, and quasi-balanced based on biological sex. This resulted in six participant groups (e.g., midlife low strength). The VOT included 3 min of rest, 5 min of ischemia, and 3 min of reperfusion to determine indices of reactive hyperemia. NIRS-VOT outcomes included the desaturation rate (i.e., first 30 s), minimal StO2 (StO2min), initial (i.e., first 10 s) rate of re-saturation (upslope), maximal StO2 (StO2max) and time to peak saturation. Separate 2×3 between factor (HG x Age Group) ANOVAs were conducted for each outcome. A p≤0.05 was considered significant, and data were presented as mean ± SD.

Results: There were no significant interactions for the outcome variables, so marginal differences were examined. Independent of strength, there was a significant main effect of Age for baseline (p<0.001, ηp 2 =0.187), and time to peak (p<0.001, 𝜂𝑝 2 =0.166) with greater values exhibited for the young compared to older group (70.4±4.2% vs. 65.0±4.9% and 42.2±10.9s vs. 32.6±7.6s). There was also a main effect of Age for downslope (p<0.001, 𝜂𝑝 2 =0.178), which compared to the young group (-0.143±0.02 %·s-1) was lower for midlife (-0.115±0.03%·s-1; p=0.001) and older adults (-114±0.03 %·s-1; p=0.002). For StO2min (p=0.028, 𝜂𝑝 2 =0.088), there was only a significant difference between young and midlife (30.1±7.2 % vs. 36.7±10.7%; p=0.023). The main effect of Age for StO2max (p<0.001, 𝜂𝑝 2 =0.396), indicated a progressive decrease across the life span (83.9±2.8% vs. 80.6±3.6% vs. 77.0±4.1%). Collapsed for age, there was a significant main effect of HG strength for downslope (p=0.023, 𝜂𝑝 2 =0.065), StO2min (p=0.019, 𝜂𝑝 2 =0.069), upslope (p=0.004, 𝜂𝑝 2 =0.101), and time to peak (p=0.025, 𝜂𝑝 2 =0.063), such that the low HG strength group had faster slopes and lower values for StO2min and time to peak.

Conclusions: The main findings included that the young low HG strength group had the greatest downslope and total magnitude of desaturation, as well as HG strength did not equally influence metrics of the reactive hyperemic phase. The downslope results partially supported the hypothesis that older adults would have slower microvascular responses. For StO2max, age appeared to elicit a stronger effect than HG strength. These findings suggested that HG strength may be most reflective of a specific portion of the vascular tree, while upslope and StO2max may be influenced by different mechanisms associated with reactive hyperemia. Notably, the participants in this study were relatively healthy based on being free of any chronic disease. Future work is necessary to determine the predictive power of NIRS-VOT parameters and its relation to HG strength.

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