Neuromuscular Control in Spasticity
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Little is known about the effects of spasticity on the excitation and recruitment of individual motor units to control muscle strength. However, it is precisely this information that would lead to a better understanding and thus to a targeted therapy of affected patients. The problem is that most patients with spasticity also suffer from paralysis of the affected muscle. It is therefore difficult to determine which change in neuromuscular activation is due to spasticity and which is due to paralysis.
To identify the effect of spasticity on neuromuscular control, we compared the excitation and recruitment of motor units of patients with spasticity with those of patients with spinal muscular atrophy (SMA). Patients with SMA suffer from paralysis but do not have spasticity. To non-invasively detect the activation of individual motor units, the HSR-EMG method developed at the RPE was used.
Characteristic changes occur in the HSR-EMG signal that distinguish pathological neuromuscular control from physiological control. These characteristic differences can be described by seven parameters. But only three of these seven parameters differ between patients with spasticity and SMA. Spasticity is thus characterized by a lower firing rate, a greater and more regular interval between individual activations and lower HSR-EMG signal energy.