ABSTRACT
The objective of this study was to test the hypothesis that muscle disuse can result in abnormal neuromuscular transmission. Six healthy volunteers (2 females, mean age = 33 years) participated in the study. Cast immobilization of one leg, for a period of 4 weeks, was used as a model of disuse; the contralateral leg was used as a control. Three testing sessions, consisting of stimulation single fiber electromyography of the soleus muscle bilaterally, were done before, immediately after, and 4 weeks after cast removal. The main outcome measure was neuromuscular jitter, measured as the mean of the consecutive differences (MCD) of single muscle fiber potentials. A mean MCD was calculated for each muscle, and the data from all subjects was pooled to calculate a sample mean MCD. The control side showed good reproducibility of results between testing sessions. The experimental side showed a significant increase of the sample mean MCD after casting when compared to: preimmobilization values (P < 0.001), and to the control side (P < 0.001). After 4 weeks of recovery, the sample mean MCD returned to preimmobilization values. This study presents evidence that muscle disuse, without any neuromuscular disease, can result in a reversible dysfunction of neuromuscular transmission.
Subject(s)
Motor Endplate/physiology , Muscles/physiology , Neuromuscular Junction/physiology , Adult , Electromyography , Female , Humans , Immobilization , Male , Middle AgedABSTRACT
Prolonged skeletal muscle disuse, during space flights and on Earth, produces distinct adaptive changes in the neuromuscular system of human subjects. There is a significant decline in muscle mass and strength, exercise capacity, fatigue resistance, integrated EMG (IEMG) output and time-dependent alterations in the behavior of Hoffman (H) and deep tendon reflexes. The objective of this study was to examine the changes in excitability of segmental motoneuronal network and its influence upon gastrocnemius-soleus (G-S) function in healthy male and female subjects, who underwent either 6 degrees head-down bedrest (HDB) or unilateral cast-immobilization (CIM) for a period of 30 days.
Subject(s)
Bed Rest , Electromyography , Head-Down Tilt , Immobilization , Isometric Contraction/physiology , Muscle, Skeletal/physiology , Adult , Female , H-Reflex , Humans , Male , Middle Aged , Motor Neurons/physiology , Muscle Fatigue/physiologyABSTRACT
Prospective electrodiagnostic studies were performed in 26 subjects with definite multiple sclerosis (MS), ranging from mildly to severely affected, to evaluate possible lower motor neuron involvement. Ten of these subjects also underwent single fiber electromyography (SFEMG) examination. Nerve conduction studies (NCS) were normal with no evidence of peripheral or entrapment neuropathies. Abnormal late responses with increased amplitude and chronodispersion of F-waves were found in 9 subjects. Abnormal recruitment patterns with decreased numbers of motor unit action potentials (MUAPs) of normal amplitude, phasicity, and firing rate were found in 9 subjects. Five of them also presented spontaneous electromyographic (EMG) activity in several muscles with no specific myotomal or peripheral nerve distribution. SFEMG showed increased jitter with no blocking in 4 of the 10 subjects studied. Thus, EMG abnormalities were present in many MS patients with no concurrent peripheral or entrapment neuropathies. Electromyographers must be aware of these abnormalities when performing routine EMG examinations in these patients.
