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(Hypertension. 2005;45:1019.)
© 2005 American Heart Association, Inc.

Original Articles

Muscle Fiber-Type Distribution as a Predictor of Blood Pressure

A 19-Year Follow-Up Study

Miika Hernelahti; Heikki O. Tikkanen; Jouko Karjalainen; Urho M. Kujala

From the Unit for Sports and Exercise Medicine (M.H., H.O.T.), Institute of Clinical Medicine, University of Helsinki, Finland; Central Military Hospital (J.K.), Helsinki, Finland; and the Department of Health Sciences (U.M.K.), Faculty of Sport and Health Sciences, University of Jyväskylä, Finland.

Correspondence to Miika Hernelahti, MD, PhD, Unit for Sports and Exercise Medicine, Töölö Sports Hall, Mannerheimintie 17, 00250 Helsinki, Finland. E-mail miika.hernelahti{at}helsinki.fi

The known association between physical activity and low blood pressure may be influenced by inherited characteristics. Skeletal muscle consists of type I (slow-twitch) and type II (fast-twitch) muscle fibers, with proportions highly variable between individuals and mostly determined by genetic factors. A high percentage of type I fibers (type I%) has been associated with low blood pressure in cross-sectional studies. We investigated whether type I percentage predicts future blood pressure levels and explains part of the association between physical activity and blood pressure. At baseline, in 1984, muscle fiber-type distribution, physical activity, and body mass index (BMI) were determined in 64 healthy men (age, 32 to 58 years). At follow-up, in 2003, blood pressure, physical activity, and BMI were determined in these men. In subjects without antihypertensive medication (n=43), type I percentage accounted for 5%/18% of the variation in systolic/diastolic blood pressure. A high type I percentage predicted, independent of both baseline (in 1984) and follow-up (in 2003), physical activity, BMI, and low systolic and diastolic blood pressure. Adjusted for all baseline covariates, a 20-unit higher type I percentage predicted a 11.6-mm Hg lower systolic blood pressure (P=0.018) and a 5.0-mm Hg lower diastolic blood pressure (P=0.018). High levels of physical activity in 1984 predicted low diastolic blood pressure, but this association was lost when type I percentage was included into the model. A high proportion of type I fibers in skeletal muscle is an independent predictor of low blood pressure and explains part of the known association between high levels of physical activity and low blood pressure.

Key Words: blood pressure • exercise • hypertension • muscles