Age and Handgrip Strength Induce Differences in Micro- and Macro-Vascular Responses
Authors: Ransom Kyndall , Traylor Miranda , Batman Genevieve , Cooper Christian , Keller Joshua 
Published: May 2024

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 and macrovascular health and function. These advances include measurements of skeletal muscle tissue oxygenation (StO2, %) with near-infrared spectroscopy (NIRS) during vascular occlusion tests (VOT) as well as carotid-femoral pulse-wave velocity (cfPWV), which is the current gold-standard to measure aortic stiffness. Although NIRS-VOT and cfPWV 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 and cfPWV between groups of low and high HG strength. We hypothesized that individuals with lower HG strength would exhibit lower vascular function. Methods: 67 adults were separated into age groups: young (19 – 40 yr), midlife (41 – 64 yr), and 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. Indices included the initial (i.e., first 10 s) rate of re-saturation (upslope) and the maximal StO2 (StO2max) percent following ischemia. Aortic stiffness was defined as cfPWV using the time difference between the appearance of the carotid and femoral pulses. Separate 2×3 between factor (HG by Age Group) ANOVAs were conducted for each outcome. A p≤0.05 was considered significant, and data were presented as mean ± SD. Results: For upslope, there was a significant interaction (p=0.042, ηp2=0.078), and follow-up analyses revealed for young and midlife adults the high HG group exhibited greater upslopes than the low strength group (young: 2.24±0.9 vs. 1.64±0.7 and midlife: 2.21±0.9 vs. 1.59±0.7%∙s−1). There was no significant interaction (p=0.360) for StO2max, but there was a significant main effect (p<0.001) of Age such that it progressively decreased across the lifespan (83.9 ± 2.0 > 80.7 ± 2.3 > 77.3 ± 2.8%). Similarly, cfPWV exhibited a significant main effect (p<0.001; ηp2 =0.429) of Age indicating aortic stiffness worsened with age, independent of HG strength. Conclusions: These results indicated that upslope was sensitive to group differences in HG strength, but only in the young and midlife age groups. For StO2max and cfPWV, age differences appeared to elicit a stronger effect than HG strength. The current findings suggested that HG strength may be most reflective of a specific portion of the vascular tree, while the initial rate of re-saturation 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 for future onset of CVD. We would like to thank the American Physiology Society for support and the University of South Alabama for allowing us to use its facilities. We would also like to thank all of the participants who agreed to adhere to the protocol and procedures of this study. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.