title: Contractile properties of motor units and expression of myosin heavy chain isoforms in rat fast-type muscle after volitional weight-lifting training.
abstract: Dynamic resistance training increases the force and speed of muscle contraction, but little is known about modifications to the contractile properties of the main physiological types of motor units (MUs) that contribute to these muscle adaptations. Although the contractile profile of MU muscle fibers is tightly coupled to myosin heavy chain (MyHC) protein expression, it is not well understood if MyHC transition is a prerequisite for modifications to the contractile characteristics of MUs. In this study, we examined MU contractile properties, the mRNA expression of MyHC, parvalbumin, and sarcoendoplasmic reticulum Ca2+pump isoforms, as well as the MyHC protein content after 5 wk of volitional progressive weight-lifting training in the medial gastrocnemius muscle in rats. The training had no effect on MyHC profiling or Ca2+-handling protein gene expression. Maximum force increased in slow (by 49%) and fast (by 21%) MUs. Within fast MUs, the maximum force increased in most fatigue-resistant and intermediate but not most fatigable MUs. Twitch contraction time was shortened in slow and fast fatigue-resistant MUs. Twitch half-relaxation was shortened in fast most fatigue-resistant and intermediate MUs. The force-frequency curve shifted rightward in fast fatigue-resistant MUs. Fast fatigable MUs fatigued less within the initial 15 s while fast fatigue-resistant units increased the ability to potentiate the force within the first minute of the standard fatigue test. In conclusion, at the early stage of resistance training, modifications to the contractile characteristics of MUs appear in the absence of MyHC transition and the upregulation of Ca2+-handling genes.
authors.affiliation: Department of Neurobiology, Poznan University of Physical Education, Poznań, Poland; Department of Motor Rehabilitation, Poznan University of Physical Education, Poznań, Poland; lochynski@awf.poznan.pl.
authors.forename: Dawid
authors.initials: D
authors.lastname: Łochyński
authors.affiliation: Department of Neurobiology, Poznan University of Physical Education, Poznań, Poland; Department of Physiology, Biochemistry, and Hygiene, Poznan University of Physical Education, Poznań, Poland.
authors.forename: Dominik
authors.initials: D
authors.lastname: Kaczmarek
authors.affiliation: Department of Neurobiology, Poznan University of Physical Education, Poznań, Poland.
authors.forename: Włodzimierz
authors.initials: W
authors.lastname: Mrówczyński
authors.affiliation: Chair of Biophysics, Poznan University of Medical Sciences, Poznań, Poland.
authors.forename: Wojciech
authors.initials: W
authors.lastname: Warchoł
authors.affiliation: Department of Muscle Physiology, Faculty of Rehabilitation, University School of Physical Education, Krakow, Poland.
authors.forename: Joanna
authors.initials: J
authors.lastname: Majerczak
authors.affiliation: Department of Cell Biology and Imaging, Institute of Zoology, Jagiellonian University, Krakow, Poland; and.
authors.forename: Janusz
authors.initials: J
authors.lastname: Karasiński
authors.affiliation: Department of Molecular Neuropharmacology, Institute of Pharmacology, Polish Academy of Sciences, Krakow, Poland.
authors.forename: Michał
authors.initials: M
authors.lastname: Korostyński
authors.affiliation: Department of Muscle Physiology, Faculty of Rehabilitation, University School of Physical Education, Krakow, Poland.
authors.forename: Jerzy A
authors.initials: JA
authors.lastname: Zoladz
authors.affiliation: Department of Neurobiology, Poznan University of Physical Education, Poznań, Poland.
authors.forename: Jan
authors.initials: J
authors.lastname: Celichowski
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D020013:Calcium Signaling / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology; D018995:Myosin Heavy Chains / Q000378:metabolism*; D010805:Physical Conditioning, Animal / Q000379:methods*; D051381:Rats; D017208:Rats, Wistar; D055070:Resistance Training / Q000379:methods*; D014836:Volition / Q000502:physiology
chemical_list: D018995:Myosin Heavy Chains
keywords: fatigue; rate coding; resistance training; skeletal muscle