An integrated EMG/biomechanical model of upper body balance and posture during human gait

The full-scale biomechanical and electromyography (EMG) analyses of the balance during human gait are required to understand the neural control of locomotion. This chapter discusses an inverted pendulum model of upper body balance in both the plane of progression and the frontal plane and a medial/lateral balance model of the total body. EMG evidence is also presented to reinforce the conclusions from the moment of force analyses. The kinematics and kinetics for up to ten natural walking trials on each of four subjects and EMG records from walking trials on eleven subjects are investigated. The results exhibit that the hip extensors/flexors have an overpowering role in maintaining dynamic balance of the head, arms, and trunk (HAT) in the plane of progression. Because of the lack of suitable neurological and biomechanical delays among the small head acceleration, presumably exciting vestibular afferents, and the hip moment patterns, the vestibular system appears not to be involved as a feedback sensor in the balance control during gait; in the frontal plane, the hip abductors are dominant in countering the large medial-lateral (M/L) imbalance of HAT during single support but are assisted by the medial acceleration of the hip joint; (3) the total body M/L balance is achieved by the M/L placement of the foot with some opposition and some assistance by the M/L acceleration of the subtalar joint; and (4) EMG profiles of the pelvic and trunk muscles indicate an active role of these muscles at each spinal level in the stabilization of the more superior segments against inertial and gravitational forces.