Effect of exercise on the motor unit

Abstract

The motoneuron part of this review deals with the changes in recruitment and firing rates of the motor unit types upon changes from a physically inactive life to endurance or strength training. The muscle fibers react to prolonged exercise by adaptation to a higher level of performance. A matter of discussion is the prerequisites for a transformation between the basic muscle fiber types, slow twitch and fast twitch, during voluntary (transsynaptic) activity, which is demonstrated after artificial nerve stimulation. The review includes current knowledge of muscle fiber transformation as an adaptive response to increased usage either by electrical stimulation or by transsynaptic neuronal activity. The metabolic adaptation related to increased endurance is reviewed with special reference to effects on muscle fibers. The increase in strength as a result of high resistance training is mainly the result of increased muscle cross-section. Whether this is solely the result of an increase in size of individual fibers or an increased fiber number is a controversial matter.

Synergy of insulin‐like growth factor‐1 and exercise in amyotrophic lateral sclerosis

“…Indeed, it has been shown that an increase in muscle strength results in more effective recruitment of motor units as well as increased cross-sectional area of the muscle. 24,25 In addition, exercise induces an increase of muscle capillary density with decreased mitochondrial density and lipid storage. Exercise has also been shown to induce neural changes, including, increased activation, increased motor synchronization, and cross-transference of strength between limbs.…”

Neuromuscular electrical stimulation in neurorehabilitation

“…225,227 The specific effect of NMES-facilitated exercise on the motor unit has been reviewed. 91 Numerous skeletal-muscle biochemical and physiological adaptations are induced by chronic low-frequency electrical stimulation in an animal model. 189 Fast to slow twitch alterations of muscle fibers are associated with alterations of calcium dynamics and myofibrillar proteins; white to red fiber transformations are associated with changes in mitochondrial enzymes, myoglobin, and the induction of angiogenesis.…”

Effects of fetal spinal cord tissue transplants and cycling exercise on the soleus muscle in spinalized rats

“…Therefore, in the present study, an exercise program involving hind limb movement similar to a bicycling motion was utilized to determine the potential influence on muscle size and MyHC expression following SCI. 15,34,45,47 …”