title: Myosin heavy chain composition of single muscle fibers in male distance runners.
abstract: The purpose of this study was to characterize the myosin heavy chain (MHC) composition of single muscle fibers from the gastrocnemius of male collegiate distance (DIST; n = 7), middle-distance (MID; n = 6), and recreational runners (REC; n = 6). Additionally, mATPase histochemistry was used to serve as a comparison to previous studies and the single fiber MHC technique. SDS-PAGE of single muscle fibers revealed a higher proportion of MHC I in DIST compared to MID and REC (74.9 +/- 4.3 vs 54.4 +/- 2.8 vs 56.2 +/- 2.9 %, respectively; p < 0.05), less MHC IIa/IIx in DIST compared to MID and REC (0.0 +/- 0.0 vs 6.0 +/- 2.4 vs 15.9 +/- 4.2 %, respectively; p < 0.05), and more total hybrids (I/IIa+IIa/IIx+I/IIa/IIx) in REC than both run groups, DIST and MID (23.0 +/- 3.3 vs 6.2 +/- 1.1 vs 13.2 +/- 2.6 %, respectively; p < 0.05). ATPase histochemistry (pH 4.54) revealed a higher percentage of type I fibers in DIST compared to MID and REC (71.1 +/- 3.1 vs 56.3 +/- 2.5 vs 59.8 +/- 2.3 %, respectively; p < 0.05), a higher percentage of type IIa in MID compared to DIST and REC (43.3 +/- 2.7 vs 28.5 +/- 3.1 vs. 30.2 +/- 3.1 %, p < 0.05), and a higher distribution of type IIb in REC than both run groups (10.0 +/- 2.7 vs 0.4 +/- 0.2 vs 0.4 +/- 0.2 %, p < 0.05). These results suggest that distance running leads to an increase in MHC I expression, training for mid-distance events leads to a prevalence of MHC IIa, and run training leads to a decrease in hybrid fibers.
authors.affiliation: Human Performance Laboratory, Ball State University, Muncie, Indiana 47306, USA.
authors.forename: M P
authors.initials: MP
authors.lastname: Harber
authors.forename: P M
authors.initials: PM
authors.lastname: Gallagher
authors.forename: J
authors.initials: J
authors.lastname: Trautmann
authors.forename: S W
authors.initials: SW
authors.lastname: Trappe
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001823:Body Composition; D005080:Exercise Test; D006801:Humans; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000201:enzymology / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism*; D010807:Physical Endurance / Q000502:physiology*; D012420:Running / Q000502:physiology*
chemical_list: D018995:Myosin Heavy Chains