Co-operated Muscular Action in Postural Adjustment and Motion in Dog, from the View Point of Electromyographic Kinesiology and Joint Mechanics

Electromyograms of fifty kinds of the skeletal muscles in dog, walking at a speed of 60m per minute and/or trotting at 90m per minute on a treadmill, have been recorded. Successive changes of joint angles are measured on photographs taken simultaneously by a camera for 16 mm roll film. The muscle activity having immediate connection with joint angulation in each period of gait, when a certain of the feet supports the body weight, takes off from and strikes on the ground and floats through the air, is discussed. The results obtained are as follows:<br>1) Constant or tonic contraction of the muscles around the axial skelet, made up of the skull and vertebral column, is basic stability of the trunk during stance and movement. Transient change of activity can however, be found in some among the stabilizers around the trunk. For example, M. spleniusstrengthenes its contraction at the moment of take-off of the fore limb and M. semispinalisincreases its activity during the period of strike and/or support. Even the muscles expected to have no direct relation to gait, such as the intercostal and abdominal muscles, participated in movment by producing successive discharges during the period of weight-support in trot.<br>2) In spite of apparent differences between the walk, a slow four-beat gait, and the trot, a diagonal two-beat gait, it is difficult to find something specific to the respective gait, concerning with EMG's patterns and joint actions, except qualitative predominency of the trot in the magnitude of activity and range size of extention in the joints.<br>3) During the period of stance which is composed of strike, weight-support and takeoff, the shoulder joints are stabilized by simultaneous action of M. supraspinatus, M. infras-pinatus and M. deltoideusetc. bilaterally, the elbow joint by M. triceps brachii(and M. anconeus) unilaterally, the carpal joint by the extensors and flexors around the fore arm bilaterally and the digital joints by elevating action of the flexors of manus unilaterally. In the period of swing, during which a foot takes off from the ground and floats through the air, a fairly smaller number of the muscles, i. e. M. deltoideus, M. branchialis and M. biceps brachii etc. present vigorous increases in activity.<br>4) Period of stance in the hind limb is mainly achieved by the bulky extensors of joints, such as the gluteus muscles on the hip joint, the quadriceps femoris on the knee joint and the gastrocnemius on the hock-joint. It is of course that their activities are assisted with the hamstrings muscles as temporary balancers and the flexors of the pes as supporterss of the digital joints. The sartorius and the anterior tibial muscle play a main role during-the period of swing, while the extensors of the digit present strenuous activity and function to determine the placement of foot at a moment of strike on the ground.<br>5) Although M. serratus, M. trapezius and M. rhomboideus act primarily as the stabilizers of the shoulder girdle in strike, they assist both flexion and extension in movement.<br>6) Being opposite to the fact that the deep portion of the pectoral muscles contracts in stance mainly, the superficial portion of them contacts in movement. But the effect of both portions is similar in adducting the fore limbs.<br>7) Increase of the joint angles in stance, the period of weight-support and decrease of them in swing, the period of propulsion of the limb are presented in a fashion of rhythmical, flowing repetition in both walk and trot. However, a temporary decrease is found in suchjoints as the shoulder, elbow, knee and digital joint at perpendicular support of the body weight, which is a position midway between strike and takeoff. At this moment the stabilizing muscles of respective joint are forced to strengthen their contractive activity remarkably.