Single muscle fiber contractile properties of young competitive distance runners

Abstract

Harber M, Trappe S. Single muscle fiber contractile properties of young competitive distance runners. J Appl Physiol 105: 629 -636, 2008. First published June 5, 2008 doi:10.1152/japplphysiol.00995.2007.-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 (m), peak force (P o; mN), unloaded contraction velocity (Vo; fiber lengths/s), and power. Maximum oxygen uptake was higher (P Ͻ 0.05) in Run (71 Ϯ 1 vs. 47 Ϯ 2 ml ⅐ kg Ϫ1 ⅐ min Ϫ1 ). Diameter of MHC I and MHC IIa fibers from Run subjects was ϳ20% greater (P Ͻ 0.05) than Rec. Peak force of the MHC IIa fibers was 31% higher (P Ͻ 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 Ͻ 0.05) in MHC I (ϩ70%) and MHC IIa (ϩ18%) fibers from Run subjects. In vitro peak absolute power (N ⅐ s Ϫ1 ) of both fiber types was greater (P Ͻ 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. myosin heavy chain; exercise; endurance SCIENTISTS HAVE LONG BEEN intrigued by the physiological attributes that allow elite athletes to achieve high levels of physical performance. Initial studies focused on describing the cardiovascular variables of champion athletes (1,9,23,35).

Making Olympic lizards: the effects of specialised exercise training on performance

“…The role of the other correspondingly different variables is less clear. The hypertrophic effects of aerobic training have been equivocal and somewhat controversial (Harber et al, 2012;Lundberg et al, 2013), but several studies have shown increased muscle mass and increased slow oxidative fibre size after aerobic exercise training in mammals, including humans (Schwartz et al, 1991;Schluter and Fitts, 1994;Trappe et al, 2006;Harber and Trappe, 2008;Harber et al, 2009Harber et al, , 2012Konopka et al, 2010;Lovell et al, 2010). However, although FCSA certainly contributes to force production, it is less clear how a larger FCSA might increase endurance.…”

“…Maximal locomotor capacities seem intuitively essential during a high-speed chase between predator and prey, for example, and some studies have detected selection on maximal locomotor capacities in nature (reviewed in Irschick et al, 2008), but it is unclear how common such scenarios actually are for free-living individuals , how often animals actually use maximal capacities (Irschick and Losos, 1999; and whether frequent use in these or other contexts alters muscle physiology to increase performance in subsequent situations that may impact fitness. In humans, both endurance running and sprint training can result in dramatic changes to skeletal muscle organisation, from gene expression (Wang et al, 2004;Wilson, 2013) to contractile properties, hypertrophy and power output (Trappe et al, 2006;Harber and Trappe, 2008;Lundberg et al, 2013). There are several studies on the effects of exercise in non-mammalian tetrapods, demonstrating that exercise training can enhance endurance capacity in amphibians (Cummings, 1979;Miller and Camilliere, 1981), crocodilians (Owerkowicz and Baudinette, 2008;Eme et al, 2009) and birds (Gaunt et al, 1990), but such studies have been conducted on only a few very distantly related species.…”

Muscle protein synthesis and gene expression during recovery from aerobic exercise in the fasted and fed states

“…Aerobically trained skeletal muscle is characterized by a high oxidative capacity and in some cases muscle fiber hypertrophy (12,13,19,21). While the mechanisms of exerciseinduced mitochondrial biogenesis have been comprehensively investigated, the alterations in muscle protein metabolism during recovery from aerobic type exercise have been less characterized.…”

Aerobic exercise training improves whole muscle and single myofiber size and function in older women

“…We recently reported that slow and fast myofibers from collegiate runners have a higher contraction velocity and generate greater peak power compared to recreationally active runners (19). Additionally, 13 wk of aerobic training increased normalized force, contraction velocity, and peak power production at the cellular level, independent of changes in muscle fiber size (47).…”

“…Historically, it is known that aerobically trained athletes display larger muscle fibers compared to controls (9,10,18,19); however, limited data are available to describe the influence of aerobic training on myofiber size in older adults. A cross-sectional analysis of older runners (63 yr) reported larger type I (slow) myofibers than younger subjects (8).…”