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Fatigue of rat hindlimb motor units: Biochemical– physiological associations
Author(s) -
Callister Robert J.,
Sesodia Sanjay,
Enoka Roger M.,
Nemeth Patti M.,
Reinking Robert M.,
Stuart Douglas G.
Publication year - 2004
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.20158
Subject(s) - hindlimb , motor unit , oxidative phosphorylation , lactate dehydrogenase , anaerobic exercise , extensor digitorum muscle , glycolysis , medicine , endocrinology , soleus muscle , succinate dehydrogenase , chemistry , malate dehydrogenase , intracellular , muscle fatigue , biology , oxidative enzyme , enzyme , skeletal muscle , anatomy , biochemistry , electromyography , neuroscience , physiology
Associations between fatigability and biochemical properties within motor unit (MU) types were explored in two hindlimb muscles of the adult rat. Type FF MUs in extensor digitorum longus and type S units in soleus were subjected either to a moderate (type FF) or severe (type S) 6‐min, fatigue‐inducing stimulation protocol. For both MU types, the range of values for their fatigability was considerably greater than the ranges in the activity levels of three enzymes in the units' constituent muscle fibers (MFs). These enzymes represented major energy‐yielding pathways: adenylokinase, for high‐energy phosphate metabolism; lactate dehydrogenase, for anaerobic glycolysis; and malate dehydrogenase, for oxidative metabolism. There were also relatively weak associations between the fatigue indices of the MUs and the activity levels of the three enzymes. Thus, this work supports previous conclusions that the force decline exhibited by MUs during electrically evoked contractions depends on both MF biochemistry and other intracellular mechanisms. Electromyographic measurements suggested that these other mechanisms are distal to the intramuscular branches of the axon in type FF units, and distal to excitation–contraction coupling in type S units. Muscle Nerve, 2004