John V. Basmajian

The Role of Muscles in Arch Support of the Foot: An Electromyographic Study

Simultaneous electromyography of six muscles in the leg and foot in twenty subjects reveals that only heavy loading elicits muscle activity. Loads of 100 to 200 pounds on one foot are borne easily by passive structures (ligaments and bones) that support the arches. With 400 pounds, the muscles do come into play, but even then many remain inactive. The first line of defense of the arches is ligamentous. The muscles form a dynamic reserve, called upon reflexly by excessive loads, including the take-off phase in walking.

Factors preventing downward dislocation of the adducted shoulder joint. An electromyographic and morphological study.

An electromyographic study of various muscles in the region of the shoulder joint in twenty-two healthy men combined with a study of dissections shows that, contrary to expectations, downward dislocation of the shoulder joint is not prevented by the vertically running muscles, for example, the deltoid, biceps, and triceps. Normally it is prevented by a locking mechanism dependent on three factors: (1) the slope of the glenoid fossa, leading to (2) the tightening of the superior part of the capsule (including the coracohumeral ligament), and (3) the activity of the supraspinatus muscle (and, to a lesser extent, the posterior fibers of the deltoid).

Functions of human thenar and hypothenar muscles; an electromyographic study of twenty-five hands.

Simultaneous electromyographic records were made from three thenar and the three hypothenar muscles of twenty-five mormal subjects, to determine the function of these muscles in various postures and grips of the hand. Extremely fine, indwelling wire electrodes were used. It was found that not all thenar muscles were active in all thumb positions, but that all hypothenar muscles were active in three basic postures of the little finger. Two somewhat different patterns activity occurred when the thumb was first softly and then firmly opposed to each of the fingers in a sequence that began at the index and ended at the little finger. The flexor pollicis brevis was dominant in firm grip, particularly in grip between the thumb and two radial fingers, but a large degree of abduction of the thumb might possibly have been a limiting factor in the activity of this muscle. The two opponents muscles seemed to act as a unit in opposition of the thumb to both the ring and little fingers. Certain activity observed in some of the six muscles and inexplicable on a morphological basis probably served to provided stability.

Electromyography: Its Structural and Neural Basis

Publisher Summary This chapter focuses on the structural and the neural basis of electromyography (EMG). The “motor unit” is both the structural and the neural basis of EMG. In normal skeletal muscles, the fibers probably never contract as individuals. Instead, small groups of them contract at almost the same moment. There now exists more than adequate proof that all the members of this group are supplied by the branches of the axon of one spinal motor neuron or anterior horn cell. The spinal motor neuron, its axon, and all the muscle fibers it supplies are called a motor unit and this complex must be considered as the functional unit of normal neuromuscular activity. The chapter discusses the structure of motor units, basic muscle function revealed by EMG, EMG technique, relation of EMG to force or tension, and fetal EMG.

Electrocardiogram in Rabbit Fetuses

Electrocardiograms were recorded by needle electrodes in 137 of 166 rabbit fetuses at 10½ to 31 days. Invariably, electrocardiograms were obtainable from the 12th day on, which in the rabbit is an early stage of development. The earliest electrocardiogram was obtained at 10 days, 22 hours, corresponding to about five weeks in human development. Sinus rhythm was evident from the start. The wave form consists of a pair of complexes 50 to 200 msec apart. The first complex is quite variable but appears to be atrial in origin; the second is surprisingly constant and appears to be ventricular.

Training of Individual Spinal Nerve Cells and its Application to Myoelectric Devices for Handicapped Patients

Abstract Artificial auditory and visual feedbacks added to the innate proprioceptive afferent impulses allow the training of single motor nerve cells in the spinal cord. This is effected in a matter of minutes or hours by displaying to human subjects the electromyographic response to their voluntary efforts and by showing them how to concentrate on the firing of individual motor units in skeletal muscles. Later, with adequate training, the artificial feedbacks may be removed without loss of the training. Optimal training requires a skilled supervisor, careful attention to each subjects innate responses and the need for rest, positive conditioning and the avoidance of negative influences such as distraction. These, of course, are environmental conditions that must be met in any training situation. Almost every subject can be trained to maintain in isolation the activity of several separate single units. Most persons can alter the frequency of discharges wilfully and can produce various rhythms deliberately. This last finding led to the application of such training to the use of multiple sets of single motor units to drive sets of electric motors. Thus, trained subjects can operate up to 4 or 5 different electric motors in a prosthesis by triggering them through separate well-controlled motor units picked up by separate intramuscular electrodes from surviving muscles. The application of this knowledge is now well advanced and promises to provide a much greater spectrum of multi-channel myoelectric prostheses. Quite as important is the application of the findings to the development of multichannel myoelectric orthotic splints in neurologically handicapped patients.