Mechanics of human isolated voluntary muscle.

Four German amputees and two recently operated American amputees were available for the present study. These subjects, severally, had had cineplastic muscle tunnels placed through the flexors and extensors of the forearm, the biceps brachii, the triceps and a portion of the pectoralis major. Since these muscles had been freed from their bony insertions and deprived of their compensating skeletal lever arms, they were admirably suited for the study of muscle action. By insertion of pegs through the tunnels, affixed to stirrups, tensions developed by the muscles under various conditions were directly measurable. Furthermore, the activity of the muscles was produced by voluntary effort, and thus fhe pattern of neurostimulation was normal. A new type of dynamometer was constructed to measure tensions, consisting of calibrated aluminum rings to which were affixed SR-4 type A-l electrical strain gauges. The distortion of the rings was less than 0.001 inch for a force of 10 pounds. The gauges were connected in a conventional Wheat&one bridge arrangement so that all gauges were additive and the bridge self-contained on the ring. This type of connection reduced to a minimum the effects of temperature drift and external connection variations. The galvanometers used for recording bridge unbalances were Heiland type A, and fhe recording instrument was the Heiland type SE-301 R-12 oscillograph. To control the possibility that the subject on approaching his maximal effort might unconsciously draw the extremity away from the dynamometer, an additional ring (compression ring) with affixed strain gauges was so placed as to record the reacting compression force from the distal end of the stump. Should no compression force be registered, it, indicated that the subject was pulling away from the apparatus and fhat spuriously high tensions were being registered. The experimental studies were divided in.to two groups: isometric muscle tension and isotonic (load-excursion) contractions.