Comparison of Cervical Musculoskeletal Kinematics in Two Different Postures of Primate During Voluntary Head Tracking

We have examined the effect on neck-muscle activation of altering whole body posture. A Rhesus monkey (Macaca mulatto) was trained to produce sinusoidal (0.25 Hz) head tracking movements in the sagittal plane when seated with trunk and head vertical or while standing in the quadrupedal position. Video-fluoroscopic images of cervical vertebral motion, and electromyographic (EMG) responses were recorded simultaneously. Results demonstrated that vertebral motion varied with body posture, occurring synchronously between all joints in the upright position and primarily at skull-C^sub i^ when in the quadrupedal position. Muscle EMG activation was significantly greater (p