The cross-bridge cycle and skeletal muscle fatigue. J Appl Physiol (1985) 2008 Feb;104(2):551-8
Date
12/29/2007Pubmed ID
18162480DOI
10.1152/japplphysiol.01200.2007Scopus ID
2-s2.0-38949101451 (requires institutional sign-in at Scopus site) 290 CitationsAbstract
The functional correlates of fatigue observed in both animals and humans during exercise include a decline in peak force (P0), maximal velocity, and peak power. Establishing the extent to which these deleterious functional changes result from direct effects on the myofilaments is facilitated through understanding the molecular mechanisms of the cross-bridge cycle. With actin-myosin binding, the cross-bridge transitions from a weakly bound low-force state to a strongly bound high-force state. Low pH reduces the number of high-force cross bridges in fast fibers, and the force per cross bridge in both fast and slow fibers. The former is thought to involve a direct inhibition of the forward rate constant for transition to the strong cross-bridge state. In contrast, inorganic phosphate (Pi) is thought to reduce P0 by accelerating the reversal of this step. Both H+ and Pi decrease myofibrillar Ca2+ sensitivity. This effect is particularly important as the amplitude of the Ca2+ transient falls with fatigue. The inhibitory effects of low pH and high Pi on P0 are reduced as temperature increases from 10 to 30 degrees C. However, the H+-induced depression of peak power in the slow fiber type, and Pi inhibition of myofibrillar Ca2+ sensitivity in slow and fast fibers, are greater at high compared with low temperature. Thus the depressive effects of H+ and Pi at in vivo temperatures cannot easily be predicted from data collected below 25 degrees C. In vitro, reactive oxygen species reduce myofibrillar Ca2+ sensitivity; however, the importance of this mechanism during in vivo exercise is unknown.
Author List
Fitts RHAuthor
Robert Fitts PhD Professor in the Biological Sciences department at Marquette UniversityMESH terms used to index this publication - Major topics in bold
Adenosine TriphosphateCalcium
Exercise
Humans
Hydrogen-Ion Concentration
Hydrolysis
Muscle Contraction
Muscle Fatigue
Muscle Strength
Muscle, Skeletal
Myofibrils
Myosins
Phosphates
Reactive Oxygen Species
Temperature
