title: Muscle fiber-type distribution as a predictor of blood pressure: a 19-year follow-up study.
abstract: 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.
authors.affiliation: Unit for Sports and Exercise Medicine, of Clinical Medicine, University of Helsinki, Finland. miika.hernelahti@helsinki.fi
authors.forename: Miika
authors.initials: M
authors.lastname: Hernelahti
authors.forename: Heikki O
authors.initials: HO
authors.lastname: Tikkanen
authors.forename: Jouko
authors.initials: J
authors.lastname: Karjalainen
authors.forename: Urho M
authors.initials: UM
authors.lastname: Kujala
mesh_terms: D000328:Adult; D001794:Blood Pressure; D015992:Body Mass Index; D003971:Diastole; D015444:Exercise; D006801:Humans; D008297:Male; D008875:Middle Aged; D018656:Muscle Fibers, Fast-Twitch / Q000201:enzymology / Q000648:ultrastructure*; D018657:Muscle Fibers, Slow-Twitch / Q000201:enzymology / Q000648:ultrastructure*; D018482:Muscle, Skeletal / Q000201:enzymology / Q000648:ultrastructure*; D009218:Myosins / Q000378:metabolism; D011237:Predictive Value of Tests; D012016:Reference Values; D013194:Staining and Labeling; D013599:Systole
chemical_list: D009218:Myosins