title: Adaptive conditioning of skeletal muscle in a large animal model (Sus domesticus).
abstract: Recognition of the adaptive capacity of mammalian skeletal muscle has opened the way to a number of clinical applications. For most of these, the fast, fatigue-susceptible fibres need to be transformed stably to fast, fatigue-resistant fibres that express the 2A myosin heavy chain isoform. The thresholds for activity-induced change are size-dependent, so although the requisite patterns of electrical stimulation are known for the rabbit, in humans these same patterns would produce type 1 fibre characteristics, with an undesirable loss of contractile speed and power. We have used histochemistry, immunohistochemistry and electrophoretic separations to evaluate a possible conditioning regime in a large animal model. Stimulation of the porcine latissimus dorsi muscle with a phasic 30-Hz pattern for up to 41 days converted all type 2X and 2A/2X fibres to 2A with only a small increase in the type 1 population, from 17% to 22%. Stimulation for longer periods increased the proportion of type 1 fibres to 52%. Based on this model, stimulation regimes designed to achieve a stable 2A phenotype in humans should deliver fewer stimulating impulses, possibly by a factor of 2, than the pattern assessed here. Any such pattern needs to be tested for at least 8 weeks.
authors.affiliation: Department of Human Anatomy and Cell Biology, University of Liverpool, UK.
authors.forename: Hazel
authors.initials: H
authors.lastname: Sutherland
authors.forename: Stanley
authors.initials: S
authors.lastname: Salmons
authors.forename: Ian R
authors.initials: IR
authors.lastname: Ramnarine
authors.forename: Massimo
authors.initials: M
authors.lastname: Capoccia
authors.forename: Adrian A
authors.initials: AA
authors.lastname: Walsh
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Jarvis
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D004558:Electric Stimulation; D005260:Female; D023421:Models, Animal; D018763:Muscle Fatigue / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology / Q000502:physiology; D018482:Muscle, Skeletal / Q000166:cytology / Q000294:innervation / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000502:physiology*; D013552:Swine
chemical_list: D018995:Myosin Heavy Chains