Enhancement of isometric ankle dorsiflexion by auto-myoelectrically controlled functional electrical stimulation on subjects with upper motor neuron lesions.

The objective of this study was to test myoelectrically controlled functional electrical stimulation of the same muscle (AutoMCS) on patients with either stroke or spinal cord injury. The paretic anterior tibialis (TA) muscle was stimulated with an amplitude controlled continuously by the volitional myoelectric signal from the same muscle. Surface electrodes were used and volitional myoelectric signals were extracted by analog/digital signal processing techniques. Isometric dorsiflexion torque of the foot was displayed on a screen and the subjects were asked to track a sinusoidal curve. Subjects with dropped foot, as a result of a stroke (CVA, n = 9) or spinal cord lesion (SCI, n = 4), performed tests without and then with AutoMCS applied to the muscle. Subjects were their own control and tracking tests without and with AutoMCS. Changes in torque range, tracking delay, and tracking control accuracy have been evaluated. A significant (p < 0.05) increase of dorsiflexion torque by AutoMCS was found. An immediate carryover effect was seen in one stroke subject. The analysis of the tracking control showed only little loss of controllability with the system. We conclude that for selected subjects this method can instantly increase the muscle force of the anterior tibialis without significantly compromising tracking control or tracking delay.