Motor units in incomplete spinal cord injury: electrical activity, contractile properties and the effects of biofeedback

Journal ofNeurology, Neurosurgery, and Psychiatry, 1990 · DOI: · Published: January 1, 1990

Simple Explanation

This study examined the electrical and contractile properties of hand muscles in quadriplegic subjects before and after EMG biofeedback. The study found spontaneously active motor units and units that could only be slowly and weakly activated, suggesting an overlap of surviving motor neurons. Biofeedback training increased the surface EMG but did not significantly change the twitch tension of single motor units or the percentage of spontaneously active units.

Study Duration

Not specified

Participants

Six adult, quadriplegic subjects (three male and three female; time since injury one to seven years; level of injury C4-C6)

Evidence Level

Not specified

Key Findings

1
Spontaneously active motor units and units that could only be slowly and weakly activated were observed, suggesting an overlap of surviving motor neurons.
2
The average twitch tension of single motor units in hand muscles of quadriplegic subjects was not significantly different from that in control subjects.
3
Surface EMG may be increased during biofeedback by using higher firing rates in motor units that can already be activated, rather than by recruiting previously unavailable motor units.

Research Summary

The electrical and contractile properties of motor units in hand muscles of quadriplegic subjects were studied before and after EMG biofeedback. The study found different classes of motor units, including spontaneously active units and those that were slowly activated. Biofeedback increased surface EMG, possibly by increasing the firing rate of already active motor units, without significantly changing twitch tension or recruiting new motor units.

Practical Implications

Therapeutic potential of biofeedback

Biofeedback can improve surface EMG signals, suggesting a potential therapeutic avenue for enhancing motor function in individuals with incomplete spinal cord injuries.

Understanding motor unit recovery

Identifying different classes of motor units after spinal cord injury helps to understand the mechanisms of neural recovery and adaptation.

Refining rehabilitation strategies

Understanding how biofeedback affects motor unit activity can help refine rehabilitation strategies to optimize motor function recovery after spinal cord injury.

Study Limitations

1
Small sample size
2
Specific population of incomplete spinal cord injuries
3
Technical difficulties in measuring firing rates during brief, maximum voluntary contractions

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