Electromyographic Kinesiology of the Hand

Electromyography and electrogoniometry were used to study movements of the normal long finger in the reported experiments. Two twenty-eight-micra wire electrodes were placed in each of the muscles driving the long finger. Electromyograms were recorded on one channel of a mirror-galvanometer oscillograph. Joint-displacement curves (electrogoniograms) for the proximal interphalangeal and metacarpophalangeal joints were recorded simultaneously through specially constructed electrogoniometers. Electromyograms and electrogoniograms were compared to discover the time relationships between muscle contraction, as evidenced by electromyographic activity, and finger motion, as shown by the joint-displacement curves. Each of the six muscles moving the long finger was tested in ten subjects, in seven test exercises. Because of the vagaries previously encountered in the behavior of the flexor digitorum superficialis, this muscle was tested with each subject's wrist joint in three different positions: extension, neutral, and flexion. The findings of this study help to elucidate the roles of the extrinsic and intrinsic muscles in controlling the finger. It was found that the interosseus-lumbricalis mechanism cannot be considered a functional unit; it includes two separate kinesiological entities—the interossei and lumbricalis. The interossei participate in interphalangeal extension only when the metacarpophalangeal joint is flexing or held flexed; the lumbricalis always takes part in interphalangeal extension. Neither the interossei nor the lumbricalis is active during closing of the full hand. This implies that the lumbricalis and flexor digitorum profundus are not synergists during hand closure. The extensor digitorum communis is active whenever the metacarpophalangeal joint is extending or is held extended. It also participates in many flexion movements of the metacarpophalangeal joint, apparently acting as a brake. The flexor digitorum profundus is the most consistently active flexor of the finger. It is sometimes joined by the flexor digitorum superficialis when the wrist is flexed. The flexor digitorum superficialis has its maximum action when the hand is being closed or held closed without flexion of the distal interphalangeal joint.