65 72 Muscular blood flow

Skeletal muscle blood flow: about 20% of cardiac output at rest, exercise hyperaemia and peripheral artery disease.

Skeletal muscle blood flow is the blood supply of the body's muscles, which make up about 40% of body weight in adults. At rest the muscles receive about 20% of cardiac output, roughly 1 L/min, and most of their capillaries are closed. During exercise, flow to working muscles increases many times over (exercise hyperaemia), and during heavy whole-body exercise the muscles receive most of the cardiac output. The muscles' demand can then compete with the maximum the heart can pump, so the body must restrain muscle vasodilation to keep blood pressure stable.

Skeletal muscleExercisePeripheral circulation

Share at rest≈ 20%

At rest≈ 1 L/min

Heavy exercisemost of cardiac output

Main regulatorslocal metabolites, sympathetic nerves

Figure 1. Resting distribution of a cardiac output of about 5 L/min (after Chapman and Mitchell, 1965). The highlighted bar shows skeletal muscle blood flow.

This application estimates regional blood flow as a percentage of cardiac output and converts it into mL/min from the calculated cardiac output. In clinical practice, organ blood flow is measured invasively or with imaging (for example indicator dilution, Doppler ultrasound, PET or MRI perfusion).

Regulation

Exercise hyperaemia results from several mechanisms acting together: the muscle pump, metabolites released by working muscle (potassium, adenosine, low oxygen), nitric oxide and prostaglandins from the endothelium, and ATP released from red cells. No single dilator explains it. Sympathetic nerves constrict muscle vessels but this effect is weakened in active muscle (functional sympatholysis), which preserves oxygen delivery while keeping blood pressure under control.

Clinical significance

Peripheral artery disease: narrowed leg arteries cannot increase flow during walking, causing pain (intermittent claudication); critical ischaemia causes pain at rest and ulcers
Heart failure: reduced cardiac output and excess vasoconstriction limit muscle blood flow and exercise capacity
Shock and hypovolaemia: muscle vessels constrict to divert blood to the heart and brain
Inactivity and ageing reduce capillary density and vasodilator capacity; regular exercise improves them

When to see a doctor

Calf or thigh pain on walking that disappears with rest, cold or pale feet, or wounds on the feet that do not heal need assessment of the leg arteries.

References

Joyner MJ, Casey DP. Regulation of increased blood flow (hyperemia) to muscles during exercise: a hierarchy of competing physiological needs. Physiol Rev. 2015;95(2):549–601. doi:10.1152/physrev.00035.2013
Vander A, Sherman J, Luciano D. Human Physiology: The Mechanisms of Body Function. 8th ed. Boston: McGraw-Hill; 2001. Fig. 14-9 (after Chapman CB, Mitchell JH. Sci Am. 1965). Data: BioNumbers BNID 109465

This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.

Published on 30 April 2024