Vascular compliance and viscoelasticity regulate human skeletal muscle blood flow at exercise onset
Bibliographic record
Abstract
At exercise onset, large and rapid rises in skeletal muscle blood flow are facilitated by reductions in vascular resistance. However, a focus on steady-state vascular resistance overlooks the contribution of vascular mechanical properties that regulate pulsatile blood flow. Therefore, this study tested the hypothesis that compliance and viscoelasticity of the skeletal muscle vascular bed regulate blood flow responses at exercise onset. We measured beat-by-beat brachial artery blood flow (Doppler ultrasound), brachial arterial blood pressure (Finometer), and heart rate (ECG) during a 2-minute supine baseline condition and for 2-minutes after a 2-second isometric handgrip exercise (IHG, handgrip dynamometer) in 16 healthy individuals (8 females, 23 ± 2 years). This protocol was repeated for IHGs performed at 20%, 40%, 60%, and 80% of maximal voluntary contraction (MVC). Vascular compliance, viscoelasticity, and resistance were calculated using a four-element modified Windkessel model. The mean ± standard deviation of maximal percent (%) change relative to baseline are reported. Two-tailed paired t-tests were performed. IHG elicited rises in blood flow (20%: Δ 166 ± 135%, 40%: Δ 272 ± 139%, 60%: Δ 341 ± 158%, 80%: Δ 397 ± 206%, all P < 0.01) and reductions in vascular resistance (20%: Δ -59 ± 12%, 40%: Δ -71 ± 11%, 60%: Δ -77 ± 8%, 80%: Δ -80 ± 7%, all P < 0.001). IHG-mediated rises in blood flow were associated with increases in vascular compliance (20%: Δ 55 ± 44%, 40%: Δ 64 ± 60%, 60%: Δ 48 ± 33%, 80%: Δ 85 ± 69%, all P < 0.01) and increases in viscoelasticity (20%: Δ 76 ± 34%, 40%: Δ 95 ± 40%, 60%: Δ 127 ± 68%, 80%: Δ 148 ± 83%, all P < 0.0001). IHG also reduced mean arterial pressure (20%: Δ -8 ± 4%, 40%: Δ -10 ± 8%, 60%: Δ -8 ± 3%, 80%: Δ -10 ± 5%, all P < 0.001). No changes were observed for heart rate (all P > 0.2). These data suggest that increases in vascular compliance and viscoelasticity regulate blood flow responses at the onset of physical exercise in humans. This work was supported by the Match of Minds Research Award by Brock University, and Natural Sciences and Engineering Research Council of Canada (NSERC). 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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".