Single muscle fiber contractile properties of young competitive distance runners.
The purpose of this investigation was to characterize the contractile properties of individual slow- and fast-twitch myofibers from highly trained distance runners. Muscle biopsies were obtained from the gastrocnemius of eight competitive runners (Run) and eight recreationally active individuals (Rec). Slow-twitch [myosin heavy chain (MHC) I] and fast-twitch (MHC IIa) myofibers were isolated and analyzed for diameter (microm), peak force (Po; mN), unloaded contraction velocity (Vo; fiber lengths/s), and power. Maximum oxygen uptake was higher (P<0.05) in Run (71+/-1 vs. 47+/-2 ml.kg(-1).min(-1)). Diameter of MHC I and MHC IIa fibers from Run subjects was approximately 20% greater (P<0.05) than Rec. Peak force of the MHC IIa fibers was 31% higher (P<0.05) in Run, whereas Po of MHC I fibers was not different between groups. No differences for specific tension (Po/cross-sectional area) were present between groups for either fiber type. Vo was higher (P<0.05) in MHC I (+70%) and MHC IIa (+18%) fibers from Run subjects. In vitro peak absolute power (microN.s(-1)) of both fiber types was greater (P<0.05) in Run (131 and 85% for MHC I and MHC IIa, respectively). Additionally, normalized power (W/l) of the MHC I fibers was 64% higher in Run, whereas no differences were noted for normalized power of MHC IIa fibers. These data indicate that highly trained endurance runners have elevated contraction velocity in both slow- and fast-twitch myofibers. These characteristics of the fast-twitch muscle fibers have not been previously reported in competitive endurance athletes and may contribute to the high level of running performance in these athletes.
Harber
Matthew
M
Human Performance Laboratory, Ball State University, Muncie, IN 47306, USA. mharber@bsu.edu
Trappe
Scott
S
D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology* / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D018995:Myosin Heavy Chains / Q000378:metabolism; D024461:Myosin Type I / Q000378:metabolism; D024462:Myosin Type II / Q000378:metabolism; D010807:Physical Endurance / Q000502:physiology*; D012420:Running / Q000502:physiology*
D024461:Myosin Type I; D024462:Myosin Type II; D018995:Myosin Heavy Chains