ELECTROMYOGRAPHIC AND JOINT-MECHANICAL STUDIES IN QUADRUPEDAL LOCOMOTION : I. WALK

Abstract

A dog was used to record the electromyograpltic activity of fifty skeletal muscles, 16-mm motion pictures and a cyclogram. From these data, activity of each muscle, musclecoordination, movement of joints, and differences between the fore and hind limb werediscussed. The results obtained are summarized as follows.(l) Many muscles of the shoulder girdle and shoulder joint were active in the stancephase, as antigravity muscles.(2) The M. triceps brachii was inactive in the aft-stance phase in which the elbowjoint was extending, whereas the M. biceps brachii increased its activity.(3) All the muscles moving the carpal and metacarpo-phalangeal joint were activein decelerating the toe and stabilizing the joint bilaterally to support the weight againstthe impact of striking the ground.(4) I-he flexors of tlte foot muscles were active mainly in the stance pl?ase. (5) Many muscles of the fore limb were especially active in the mid- and aft-stanceplaase, whereas those of tlte hind limb produced activity just before and after strikingtlte ground. There was a marked difference in movement between the fore and the hindlimb. The fore limb landed on the ground whiclr was most apart from the vertical linedrawn from the center of gravity of the body. On the other hand, the hind limb landedat a site of the ground which was nearest to this vertical line. Hence, the fore limb hadnot to make a structure as a weight-bearing bracer in the fore-stace phase, whereas thehind limb had to make this structure as soon as it struck the grountd. This is becausethe hind limb had to support the weight of the body at once and its muscles showedstrong activity just before and after the stance plxase.(6) The electromyographic activity pattern of tlae fore-limb muscles, wlaich aresituated nearer the center of gravity of the body, was very mucla complicated, unlikethat of the hind-limb muscles. This finding suggested tl?at tlae fore limb might play amore important role as a balancer than as a propeller.