Exploring Autonomic Responses to Acute Isometric Handgrip Exercise in Black and White Individuals

The elevated rates of cardiovascular disease in Black individuals have, in part, been attributed to the social determinants of health and subsequent elevated levels of stress stimulating overactive sympathetic and blunted parasympathetic neural control. Heart rate variability (HRV) is a non-invasive method widely used to evaluate the state of cardiac autonomic nervous system function Purpose: The purpose of this study was to observe the autonomic responses in White and Black individuals in response to an isometric handgrip exercise when controlling for perceived stress levels. Hypothesis: We hypothesize that White individuals will have a higher resting HRV and greater parasympathetic reactivation after exercise. Methods: Participants rested in the supine position for baseline measurements followed by a 3-min isometric handgrip exercise at 30% of maximal force followed by recovery. Data collected via LabChart software (ADInstruments). Beat-to-beat blood pressures (BP) and heart rates for resting and recovery were averaged over two minutes, and peaks were obtained from the last 30 seconds of the isometric handgrip exercise. Total peripheral resistance (TPR) was calculated as BP divided by cardiac output with stroke volume derived from the Modelflow using Labchart non-invasive cardiac function packages. Analysis of HRV were obtained through averages of 3-minute at baseline, during and immediately after handgrip exercise from a continuous electrocardiogram. The root mean square of successive differences between normal heartbeats (RMSSD), high frequency (HF), and low frequency (LF) powers of HRV were natural log-transformed for statistical analyses because of their skewed distribution. Two-way repeated measures of analysis of variance (ANOVA) were used (race by time). Changes in heart rate, BP, and TPR were used to explore sympathetic responses to exercise. The Perceived Stress Scale, McArthur Scale of Subjective Social Status, and General Ethnic Discrimination Scale were used to assess social status and stress. To evaluate the influence of perceived stress, ANCOVA was used with stress as a covariate. Results: All participants, n=27 (n=8, Black), were healthy and recreationally active, with a mean age of 23±4 yrs and BMI of 26±6 kg/m2. There were no differences in baseline demographics including age, sex, BMI, and employment status. Black individuals had higher perceived stress (20 vs 13; P =.023), lifetime discrimination (42 vs 24; P =.007), and stress from discrimination (42 vs 24; P <.001). Heart rate and BP increased 30 mmHg and 16 bpm, respectively, from baseline to exercise ( P <.001). There was a mean decrease of 7 mmHg in recovery BP ( P =.005), with no differences in heart rate compared to rest. There was no change TPR across time. There were no differences in BP, heart rate, TPR, RMSSD, HF, and LF between Black and White individuals at baseline, during exercise, or recovery. Additionally, there were no racial differences in these hemodynamic and autonomic variables when controlling for stress. Conclusion: Our preliminary data suggests that there are no differences between young and healthy Black and White individuals for parasympathetic withdrawal during handgrip exercise or parasympathetic reactivation during recovery. This observation holds true when controlling for the individuals perceived stress levels, due to systemic racism. Additionally, while exercise stimulates sympathetic, there were no differences by race for sympathetic activation from a 30% isometric handgrip exercise. Future research is warranted to explore whether chronic stress serves as a mediator of these autonomic responses in older populations who may have endured prolonged exposure to systemic racism. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.