Exploring vascular mechanical properties regulating blood flow during rhythmic handgrip exercise in humans

This study tested the hypothesis that vascular compliance and viscoelasticity in the skeletal muscle vascular bed regulate blood flow to the active forearm muscle during rhythmic handgrip (RHG) exercise. Beat-by-beat heart rate (HR; ECG), brachial artery blood flow velocity (Doppler Ultrasound), mean arterial pressure (MAP; Finometer), and cardiac output (CO) were measured in eleven healthy young participants (6 females, 20-27 years) during 5-minute baseline (BSL) condition followed by 5-minutes of RHG exercise (work/rest schedule: 1 second at 40% of maximal voluntary contraction /2 seconds rest). A four-element modified Windkessel model quantified beat-by-beat vascular resistance, compliance, and viscoelasticity from blood pressure and flow velocity waveforms. Brachial artery blood flow was calculated as the product of mean blood velocity and brachial artery cross-sectional area. Repeated-measures one-way analysis of variance (ANOVA, α = 0.05) provided statistical comparisons between BSL and minutes 1 (RHG-Min1), 3 (RHG-Min3), and 5 (RHG-Min5) of RHG. Data are reported as mean ± SD. Post hoc analysis was used to compare minutes 1, 3 and 5 of RHG to BSL. RHG exercise increased blood flow (BSL: 73 ± 35; RHG-Min1: 306 ± 155; RHG-Min3: 392 ± 200; RHG-Min5: 400 ± 219 mL/min; P main effect < 0.0001; all P post hoc < 0.0001 ) and reduced vascular resistance (BSL: 15 ± 8; RHG-Min1: 4 ± 1; RHG-Min3: 3 ± 0.8; RHG-Min5: 3 ± 0.9 mmHg/cm/s; P main effect < 0.0001; all P post hoc < 0.0001 ). RHG increased viscoelasticity (BSL: 0.37 ± 0.15; RHG-Min1: 0.86 ± 0.34; RHG-Min3: 0.98 ± 0.50; RHG-Min5: 0.99 ± 0.48 mmHg/cm/s; P main effect < 0.0001; all P post hoc < 0.0001 ) but did not affect compliance (BSL: 0.0017 ± 0.0005; RHG-Min1: 0.0021 ± 0.0007; RHG-Min3: 0.0023 ± 0.0010; RHG-Min5: 0.0020 ± 0.0008 cm/s/mmHg; P main effect = 0.14; all P post hoc > 0.05 ). Also, RHG increased HR (BSL: 69 ± 13; RHG-Min1: 73 ± 13; RHG-Min3: 75 ± 14; RHG-Min5: 76 ± 14 bpm; P main effect < 0.0001; all P post hoc < 0.05 ), CO (BSL: 6.3 ± 1.7; RHG-Min1: 6.9 ± 1.9; RHG-Min3: 7.0 ± 1.9; RHG-Min5: 7.1 ± 1.8 L/min; P main effect < 0.0001; all P post hoc < 0.01 ), and MAP (BSL: 93± 9; RHG-Min1: 98 ± 9; RHG-Min3: 100 ± 8; RHG-Min5: 101 ± 8 mmHg; P main effect < 0.0001; all P post hoc < 0.001 ). Therefore, these data highlight a role for vascular mechanical properties such as viscoelasticity in the regulation of human skeletal muscle blood flow during dynamic exercise. This work was funded by Brock University Horizon Scholarship, Ontario Graduate Scholarship, and Natural Sciences & Engineering Research Council of Canada Discovery Grant. 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.