Training status augments mechanisms of rapid-onset vasodilation in healthy young adults

Rapid onset vasodilation (ROV) is the immediate, transient increase in muscle blood flow following contraction and is mediated by chemical, mechanical, and, potentially, neural mechanisms. Although exercise training has been shown to preserve ROV in older adults, it remains unclear whether training promotes adaptation in specific contributing mechanisms. This study tested the hypothesis that a history of forearm training increases ROV. Sixteen healthy young males (8 trained and 8 sedentary) completed two trials of 1 s voluntary forearm contractions (5, 10, and 15 kg; 20% and 100% of maximal voluntary contraction), electrically stimulated involuntary contractions (5 and 10 mA), and mechanical forearm compression (50, 200, and 300 mmHg; randomly ordered). Forearm blood flow (ultrasound) and mean arterial pressure (finger photoplethysmography) were measured beat-to-beat and used to calculate forearm vascular conductance (FVC). Data from the two trials of each contraction/compression were averaged together to form a singular response. Forearm and hand lean mass, as measured via dual-energy X-ray absorptiometry, did not differ between groups. Trained participants displayed greater absolute ROV responses to voluntary and involuntary contractions (P ≤ 0.05 for all), as well as to higher-intensity mechanical compressions (P ≤ 0.05 for 300 mmHg ΔFVC_total, 200 mmHg and 300 mmHg ΔFVC_peak). In addition, ROV responses increased disproportionately with absolute voluntary contraction intensity in trained participants (training status × intensity interaction ΔFVC_total: P = 0.02, [Formula: see text] = 0.29). These findings extend upon previous research which has demonstrated training-related preservation of ROV and indicate that exercise training enhances rapid vascular responsiveness across multiple stimulus modalities, providing new insight into training-induced adaptations in vascular regulation.NEW & NOTEWORTHY Our study indicates that individuals with a recent history of forearm exercise training exhibit greater rapid onset vasodilatory responses compared with sedentary individuals. These findings provide novel evidence that exercise training augments rapid vascular responsiveness to both brief muscle contraction and mechanical compression in young healthy adults.