Sagittal plane analysis of head, neck, and trunk kinematics and electromyographic activity during locomotion.

STUDY DESIGN: Descriptive study examining kinematic and electromyographic (EMG) patterns of the upper body during walking. OBJECTIVE: To examine trunk, neck, and head movements to determine a mechanism for upper body stabilization during walking. BACKGROUND: Dynamic balance of the upper body during walking provides a stable base for function of sensory systems. Prior investigations of upper body motion during walking were limited to examination of isolated segments, or examination of the upper body as a single unit. In our study, the upper body is examined as 3 segments: the trunk, neck, and head. METHODS AND MEASURES: Sagittal plane walking patterns were examined in 8 unimpaired young adults. Markers placed on the trunk, neck, and head segments were recorded on videotape. Angles were calculated with respect to an external horizontal reference to determine segment position relative to space. EMG measures were obtained from erector spinae, rectus abdominus, semispinalis capitis, and sternocleidomastoid muscles. RESULTS: Results showed dynamic stability was accomplished through maintenance of a posture where the trunk was flexed, the neck was extended and the head was flexed. The trunk segment demonstrated greatest stability with the neck being the least stable of the 3 segments. Movements of upper body segments showed a tendency for the head and neck to move opposite to the trunk. EMG data demonstrated erector spinae muscle activity occurring near heel contact of each limb followed by trunk extension. The remaining muscles exhibited variable patterns of activity. CONCLUSIONS: These data indicate that movements of the upper body help to maintain a posture that promotes stability of these segments during walking. The trunk was the most stable of the three segments thereby, providing a stable platform for head and neck movement. Erector spinae muscle activity contributed to upper body movements by extending the trunk to maintain balance at heel contact. These results provide a basis for studying changes in dynamic stability that occur with age.