Time course of changes in EMG activity of fast muscles after partial denervation

Abstract

After partial denervation, the remaining motor units (MUs) of adult fast extensor digitorum longus muscle (EDL) expand their peripheral field. The time course of this event was studied using tension measurement and recordings of electromyographic (EMG) activity. The results show that after section of the L4 spinal nerve, when only 5.3 +/- 0.63 of the 40 MUs normally supplying EDL muscle remain, the force of individual motor units starts to increase between the 1st and 2nd week after the operation and continues to do so for a further week. The drastic reduction of the number of motoneurones supplying the fast EDL leads to an increase in activity of the remaining MUs. In the 1st week after partial denervation, there was a sharp increase in the EMG activity of remaining motor units. During the next 12 days, this increase became less marked, but EMG activity remained nevertheless significantly higher than that of the unoperated EDL muscle. Many MUs became tonically active during posture. The EMG activity pattern during locomotion was also altered, so that the burst duration was positively correlated with the step cycle duration. Moreover, shortly after partial denervation, the interlimb coordination was disturbed but returned to its original symmetrical use 1-2 weeks later.

A specific force deficit exists in skeletal muscle after partial denervation

“…In many previous studies, partial denervation of skeletal muscle has been accomplished by sectioning the L4 ventral lumbar root or spinal nerve, either alone or in combination with those from L5. 30,32,36 Inducing partial denervation in such a manner creates an excellent model for spinal cord injury but cannot represent peripheral nerve injury nearly as well. As L4 contributes to every motor nerve in the leg, its ablation impacts all lower extremity muscles, not just the one analyzed in a particular study.…”

Treatment with Riluzole Restores Normal Control of Soleus and Extensor Digitorum Longus Muscles during Locomotion in Adult Rats after Sciatic Nerve Crush at Birth

“…[23, 24]. Similarly, studies on rats with 13–17 MUs in Sol muscles after partial denervation inflicted at 5 days of age [25, 26, 27] showed the activity of this muscle was shorter by 3 to 36% compared to the control muscle. The observed decrease in the activity duration was consistent with the decrease in the regression slope.…”

“…However, the locomotor EMG activity of Sol and EDL muscles with SNC inflicted early after birth has been assessed in two studies by Navarrete and Vrbová [23] and Vejsada and colleagues [24]. Furthermore, data from quantitative analysis of muscle activity performed by Sławińska and colleagues [25, 26, 27] has been obtained for muscles with partial denervation. In none of these studies was the activity of both control muscles and muscles with nerve injury recorded simultaneously for the Sol and EDL muscles.…”

Identification of the effects of peripheral nerves injury on the muscle control - A review

“…The analysis of EMG muscle activity during unrestrained locomotion was used more frequently in the previous studies [e.g. 11,16,17,20,8]. However, the quantitative analysis was limited to the homologous muscle pairs, whereas the characteristics of the antagonistic muscle activities including their recruitment and coordination were assessed qualitatively only as was showed in given above publications and the recent one [14].…”

“…However, the quantitative analysis was limited to the homologous muscle pairs, whereas the characteristics of the antagonistic muscle activities including their recruitment and coordination were assessed qualitatively only as was showed in given above publications and the recent one [14]. The main symptom of impairment were changes in the activity duration as well as in the relationship between the durations of muscle activity and step cycle [16,17,20,8,14]. Generally in rats with sciatic nerve crushed the activity of extensor muscles was shorter whereas the activity of flexors was distinctly longer compared to those of non- A severe deficit of muscle control observed in a few studies before [17,20,8] and recently [14,6] was an excessively long activity of flexor muscles resulting in the coactivation with the activity of extensors.…”