Kinetic analysis of dynamic transitions in stance support accompanying voluntary leg flexion movements in hemiparetic adults.

The purpose of this study was to examine the extent to which adult hemiparesis due to cerebrovascular accident may alter the dynamic transitions from bipedal to single limb stance that accompany rapid voluntary single leg flexion movements while standing. Eight postacute hemiparetic adults performed rapid single-leg-flexion movements with the paretic (PL) and nonparetic (NL) limbs while standing on two separate force platforms that recorded the individual and resultant lateral horizontal (FY) ground reaction force (GRF) components acting on the body in the frontal plane. The results showed that for NL movements, the ipsilateral FY force-time integral contributed a significantly greater proportion to the resultant FY than that recorded beneath the upcoming stance PL, whereas PL movements showed a reverse trend indicating differences in the spatial distribution of GRFs. For some subjects, delays in the initial FY onset times between limbs and reversals in the normal direction of initial force application beneath the PL were observed. Such changes in the spatial and temporal aspects of GRF production may affect dynamic lateral weight transfer function regardless of the direction of total body motion. Implications for clinical practice pertaining to interventions that emphasize speed as well as magnitude of paretic muscle torque production, and factors related to the selection of movement activities for the retraining of dynamic weight transfer function are discussed.