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Experiments clearly demonstrate that with the help of auditory and visual cues man can single out motor units and control their isolated contractions. Experiments on the training of this control, interpreted as the training of descending pathways to single anterior horn cells, provide a new glimpse of the fineness of conscious motor controls. After training, subjects can recall into activity different single motor units by an effort of will while inhibiting the activity of neighbors. Some learn such exquisite control that they soon can produce rhythms of contraction in one unit, imitating drum rolls, etc. The quality of control over individual anterior horn cells may determine rates of learning.

Forty-four patients with hemiplegia following stroke and 10 nondisabled subjects were studied to examine the contributions inadequate motor unit recruitment and co-contraction attributable to impaired antagonist inhibition play in the movement disorder of the hemiplegic arm. Electromyographic data were recorded from agonist and antagonist muscles while subjects attempted six specified tasks. Data from subjects who could complete the tasks were compared with those who could not complete the tasks. Differences between the two groups were found in the electromyographic data obtained from the agonist muscles. Electromyographic values were consistently and significantly lower in patients who were unable to complete the tasks than in patients who were able to complete the tasks. In the antagonist muscles, a significant difference was noted only once; in this case, the EMG values were again lower in the group of patients who were unable to complete the task. Inadequate recruitment of agonists, not increased activity in the antagonists, was a consistent finding in patients who were unable to carry out the movement tasks. This study theoretically supports aiming treatment efforts at improving motoneuron recruitment rather than reducing activity in antagonists while retraining arm function.

In 29 normal persons with complete dental arches, the muscular activity of the temporalis, masseter, medical pterygoid, anterior belly of the digastric, mylohyoid and geniohyoid muscles was studied electromyographically with bipolar fine wire electrodes during various mandibular movements--both resisted and unresisted. Action potentials were recorded on FM magnetic tape and each experiment was also videotaped. Temporalis muscle was active during centric closing of the jaw with either contact of the teeth, or against resistance; during free lateral movements to the ipsilateral side, either against resistance or occlusal contact; during incisor gum chewing, molar gum chewing on ipsilateral or contralateral sides, during normal mastication; and during forceful centric occlusion. Activity occurred in the masseter and medial pterygoid muscles during the following movements; closing the jaw slowly either without occlusal contact or with occlusal contact and against resistance; free lateral movement to contralateral side, either against resistance or with occlusal contact; protraction of the jaw either without occlusal contact or with occlusal contact; swallowing either saliva or water; incisor gum chewing with either the ipsilateral or contralateral molars; normal mastication; and during forceful centric occlusion. Activity occurred in the digastric, mylohyoid and geniohyoid muscles during the following movements; opening of the jaw either slowly or maximally against resistance; closing the jaw against resistance; free lateral movement to ipsilateral and contralateral sides, either against resistance or with occlusal contact; protraction against resistance of the jaw either without or with occlusal contact; swallowing saliva and water; and protraction of the tongue. They work in antagonism (reciprocally) during gum chewing and normal mastication.

Electromyography with fine-wire electrodes and special equipment for synchronized motion pictures were used to study six muscles of the leg and foot during walking in five different ways in ten "normal" and ten flatfooted subjects. Detailed analyses and comparisons of the two groups are described and discussed.Tibialis Anterior has two peaks of activity at heel-strike and toe-off of the stance phase; is inactive during mid-swing and middle of the stance phase; is active at fullfoot in flatfooted subjects, and generally more active during toe-out and toe-in walking. Tibialis posterior is inactive through the swing phase. In flatfooted persons it becomes activated at heel-strike and more active at full-foot during level walking. The toe-out position reduces its activity. Flexor hallucis longus is most active in mid-stance; during toe-out walking, activity increases in both phases, generally being more active in "normal" persons. Peroneus longus is most active at mid-stance and heel-off and generally more active in flatfooted persons. Abductor hallucis and Flexor digitorum breuis are generally more active in flatfooted persons. A n important regular pattern of inversion and eversion during the walking cycle is described. Contingent arch support by muscles rather than continuous support is the rule, muscles being recruited to compensate for lax ligaments and special stresses during the walking cycle.

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