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, 8 sedentary) completed two trials of 1s voluntary forearm contractions (5, 10, 15kg; 20% and 100% of maximal voluntary contraction), electrically-stimulated involuntary contractions (5 and 10mA), and mechanical forearm compression (50, 200, 300mmHg) (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 (DXA), 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 300mmHg ΔFVC total , 200mmHg and 300mmHg ΔFVC peak ). Additionally, ROV responses increased disproportionately with absolute voluntary contraction intensity in trained participants (Training Status x Intensity interaction ΔFVC total : p = 0.02, η p 2 = 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.