Fatigue of muscles weakened by death of motoneurons.
Weakness is a characteristic of muscles influenced by the postpolio syndrome (PPS), amyotrophic lateral sclerosis (ALS), and spinal cord injury (SCI). The strength deficits relate to changes in muscle use and to the chronic denervation that can follow the spinal motoneuron death common to these disorders. PPS, ALS, and SCI also involve variable amounts of supraspinal neuron death, the effects of which on muscle weakness remains unclear. Nevertheless, weakness of muscle itself defines the functional consequences of these disorders. A weaker muscle requires an individual to work that muscle at higher than usual intensities relative to its maximal capacity, inducing progressive fatigue and an increased sense of effort. Little evidence is available to suggest that the fatigue commonly experienced by individuals with these disorders relates to an increase in the intrinsic fatigability of the muscle fibers. The only exception is when SCI induces chronic muscle paralysis. To reduce long-term functional deficits in these disorders, studies must identify the signaling pathways that influence neuron survival and determine the factors that encourage and limit sprouting of motor axons. This may ensure that a greater proportion of the fibers in each muscle remain innervated and available for use.
Thomas
Christine K
CK
The Miami Project to Cure Paralysis, Lois Pope LIFE Center, 1095 NW 14th Terrace (R-48), Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL 33136, USA. cthomas@miami.edu
Zijdewind
Inge
I
D000690:Amyotrophic Lateral Sclerosis / Q000503:physiopathology*; D016923:Cell Death; D006801:Humans; D009046:Motor Neurons / Q000473:pathology*; D018763:Muscle Fatigue; D009132:Muscles / Q000294:innervation / Q000503:physiopathology; D016262:Postpoliomyelitis Syndrome / Q000503:physiopathology*; D013119:Spinal Cord Injuries / Q000503:physiopathology*