Impact of Priming Exercise Load in Vascular Occlusion Test Outcomes

Near-infrared spectroscopy combined with a vascular occlusion test (NIRS-VOT) assesses microvascular function by analyzing tissue oxygen saturation (StO2). StO2-derived outcomes from the NIRS-VOT have been shown to differ across biological sex and fitness and are interpreted as reflecting differences in muscle oxidative capacity, microvascular function, and endothelial health. These differences may be influenced by the accumulation of metabolic byproducts that modulate local oxygen delivery. Exercise performed before a NIRS-VOT can alter metabolic rate, potentially influencing StO2 responses. However, it is unclear whether different submaximal priming exercise intensities affect NIRS-VOT outcomes, particularly when the magnitude of the ischemic stimulus is standardized. Clarifying this is important for improving the interpretation and mechanistic understanding of NIRS-VOT. PURPOSE: The purpose of this study was to examine changes in StO2-derived outcomes following two distinct submaximal, non-fatiguing handgrip exercise tasks. METHODS: 6 healthy adults (5 men; 27 ± 7 yrs; 76.1 ± 8.0 kg) completed two NIRS-VOT on two separate visits. The NIRS-VOT protocol included a cuff wrapped around the participants’ upper arm and inflated to 250 mmHg. After baseline, the cuff was inflated until StO2 reached 40% or for up to 5 minutes. A 30-s linear slope coefficient was calculated during the transient ischemia phase and defined as Downslope. Once 40% StO2 or the 5-min limit was observed, the cuff was deflated, and re-saturation metrics were calculated. These included Upslope (linear slope coefficient across the first 10 seconds of reperfusion) and StO2max (the greatest StO2 value observed during reperfusion). Subsequently, maximum handgrip strength (MVIC) was measured to determine exercise loads. Participants were randomized to one of two volume-matched priming exercise protocols: 60 static handgrips at 25% MVIC or 20 static handgrips at 75% MVIC. Following the exercise, NIRS-VOT was immediately repeated. For each outcome, a two-way repeated-measures ANOVA was conducted with Condition (25% vs. 75%) and Time (pre vs post). A p