Events of the excitation-contraction-relaxation (E-C-R) cycle in fast- and slow-twitch mammalian muscle fibres relevant to muscle fatigue.
The excitation-contraction-relaxation cycle (E-C-R) in the mammalian twitch muscle comprises the following major events: (1) initiation and propagation of an action potential along the sarcolemma and transverse (T)-tubular system; (2) detection of the T-system depolarization signal and signal transmission from the T-tubule to the sarcoplasmic reticulum (SR) membrane; (3) Ca2+ release from the SR; (4) transient rise of myoplasmic [Ca2+]; (5) transient activation of the Ca2+-regulatory system and of the contractile apparatus; (6) Ca2+ reuptake by the SR Ca2+ pump and Ca2+ binding to myoplasmic sites. There are many steps in the E-C-R cycle which can be seen as potential sites for muscle fatigue and this review explores how structural and functional differences between the fast- and slow-twitch fibres with respect to the E-C-R cycle events can explain to a great extent differences in their fatiguability profiles.
Stephenson
D G
DG
School of Zoology, La Trobe University, Bundoora, Victoria, Australia.
Lamb
G D
GD
Stephenson
G M
GM
D000818:Animals; D006801:Humans; D008322:Mammals; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology*