Patterns of muscle activation accompanying transitions in stance during rapid leg flexion

The organization of electromyographic, ground reaction force, and total body kinematic responses accompanying dynamic transitions from bipedal to unipedal stance during rapid leg flexion movements was examined in healthy human subjects. An impulse-momentum model of motion of the centre of body mass (CM) was used to predict the patterns of muscle activation among bilateral hip abductor-adductor muscles with respect to the primary task muscle. The results indicated an intralimb and interlimb coupling of hip muscle activations which preceded and accompanied the leg flexion response and were compatible with contributing to increasing and subsequently reducing momentum of the CM in the frontal plane. Overall, the findings suggested that the coordinative interaction of postural and intended movement components may be a reflection of the mechanical constraints inherent to stance alteration function.