Acute Exercise Effects on Blood Flow: Cardiovascular Physiology
Exercise triggers immediate cardiovascular adjustments to meet skeletal muscle O₂ demand (up to 20–50× resting).
Key Acute Responses
- Active muscle vasodilation: Metabolic (adenosine, K⁺, H⁺, NO, prostaglandins) + endothelial (shear stress) + sympathetic cholinergic → ↓ vascular resistance 80–90% in working muscle.
- Sympathetic vasoconstriction: α-adrenergic → splanchnic, renal, cutaneous beds (↑ resistance) — redistributes flow.
- Cardiac output ↑: HR (up to 200 bpm) × SV (↑ contractility, ↓ ESV, ↑ venous return) → 4–6× resting.
- Mean arterial pressure ↑: Moderate (↑ CO > ↓ TPR); systolic ↑↑, diastolic stable/slight ↓.
- Cutaneous vasodilation (delayed): Thermoregulation → redirects blood to skin → competes with muscle.
- Splanchnic/renal flow ↓: Up to 80% reduction at high intensity.
- Coronary flow ↑: Metabolic autoregulation matches myocardial O₂ demand.
- Cerebral flow: Maintained (autoregulation); slight ↑ with hypercapnia.
Hemodynamic Summary
| Vascular Bed | Flow Change | Mechanism |
|---|---|---|
| Active muscle | ↑↑↑ (20–50×) | Metabolic + endothelial + sympathetic cholinergic |
| Skin (early) | ↓ | Sympathetic α-constriction |
| Skin (late/heat) | ↑↑ | Thermoregulatory override |
| Splanchnic/renal | ↓↓ | Sympathetic α-constriction |
| Brain | ↔/↑ | Autoregulation + CO₂ |
| Heart | ↑↑ | Metabolic autoregulation |