Smooth muscle
Involuntary muscle lining organs and blood vessels, working without conscious control.
Smooth muscle lacks the striped appearance of skeletal muscle and is not under voluntary control. It lines the gut, airways, bladder, uterus and the walls of blood vessels, contracting slowly and sustaining tension with very little fatigue.
It matters to fitness in ways that are easy to overlook. Smooth muscle in the arteries sets vascular tone and so blood pressure; smooth muscle in the gut drives the transit that fibre influences; smooth muscle in the airways is what constricts in exercise-induced asthma.
In practice you do not train it directly, but aerobic exercise improves the endothelial signalling that governs it, which is part of why regular cardio lowers blood pressure.
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Written and reviewed by Mathew Beale, MSc Biotechnology, University of Reading.
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