EMG analysis of voluntary elbow movements in subjects with spasticity

Surface electromyography (EMG) signals were measured from the biceps brachii (BIC), the brachioradialis (BRD) and the triceps brachii (TRI) of seven young adults with pure spastic quadriplegia and eight normal individuals. The signals were analyzed in both the time domain and the frequency domain. The subjects sat in an adjustable chair and were asked to perform two voluntary tasks involving the elbow joint. For task A, the subjects moved the hand from the proximal target plate to the distal target plate and then back to the proximal one along the table plane. For task B, the subject followed the sound of a metronome (0.5 Hz), perform 5 elbow flexion/extension cycles in the vertical plane. Certain quantitative parameters were identified as statistically significant in describing quantitatively the condition of spasticity. Compared to the normal subjects, the spastic subjects showed significantly higher EMG activities for both the elbow flexors and extensor. The stretch/shortening (S/S) ratios for BRD and TRI were significantly different from those of the normal subjects. The power spectra analysis showed higher mean power frequency (MPF). MPF of BIC and TRI were uncorrelated for normal subjects, but correlated for the spastic subjects. It is speculated that low motor unit discharge rate and fiber type abnormalities may account for these differences.