One- or two-legged standing: what is the more suitable protocol to assess the postural effects of the rigid ankle orthosis?

To highlight the capacity of one- and two-legged standing protocols when assessing postural behavior induced by a rigid ankle orthosis, 14 healthy individuals stood upright barefoot and wore either an elastic stocking on the preferred leg or a rigid orthosis with or without additional taping in one- or two-legged (TL) conditions. Traditional center-of pressure (CP) measures were evaluated for the total two-feet resultant CP and under the feet (plantar CP). Focusing on the plantar CP displacements under the leg fitted with the various orthoses demonstrated particular postural behaviors for traditional parameters with main effects along the mediolateral axis. Only the TL protocol showed the limiting effects of the rigid shells on the inversion-eversion movements in healthy individuals.

Contribution of each lower limb to upright standing in stroke patients.

BACKGROUND AND PURPOSE: To analyze the postural behavior of standing stroke patients: (1) To differentiate between postural impairment attributable to the neurological condition (deficits attributable to the cerebral lesion) and postural impairment attributable to new mechanical constraints caused by body weight asymmetry; (2) To assess the involvement of each limb in the postural impairment; (3) To better understand which clinical deficits underlie the postural impairment. METHODS: The posturographic characteristics of each limb in 41 stroke patients (first hemispheric stroke: 16 left, 25 right cerebral lesions) required to stand in their preferred posture were compared to those in 40 matched healthy individuals required to stand asymmetrically. RESULTS: Compared to normal individuals in a similar asymmetrical posture, stroke patients were more unstable. The weight bearing asymmetry and the lateral postural instability were mainly related to spatial neglect. The paretic limb was unable to bring into play a normal longitudinal pattern of the center of pressure, which reflects an impaired stabilization control. Overall postural instability occurred when the strong limb was unable to compensate for the postural impairment of the paretic limb. CONCLUSIONS: The weight bearing asymmetry of standing stroke patients is not the primary cause of their postural imbalance, which is rather the consequence of impaired control of postural stabilization involving both limbs. Weight bearing asymmetry may not be the principle target of rehabilitation programs aiming at restoring standing balance after stroke. Instead it is suggested that more account should be taken of the compensatory role of the strong limb.

Posturography in patients with stroke: estimating the percentage of body weight on each foot from a single force platform.

BACKGROUND AND PURPOSE: Posturography in patients with stroke is widely based on the use of a single force platform and the weightbearing asymmetry quantified from the lateral shift of the center of pressure toward the sound leg. Because the percentage of body weight on each side is a more concrete variable, the present study analyzed the possibility of inferring percentage of body weight from center of pressure. METHODS: Forty-five hemiparetic subjects were asked to stand on a dual platform in a standardized position 3 months after a hemispheric stroke. First, the relationship between the %BW on each foot and the lateral shift of center of pressure was established. Second, the model was tested with a healthy subject standing on a single force platform. RESULTS: The percentage of body weight may be simply modeled from the center of pressure shift, a center of pressure displacement of 10 mm corresponding to a 5% increase in body weight on this side (r=0.97, P<0.001). This linear model is reliable, accurate, and may be generalized to other stand widths. CONCLUSIONS: This finding should be useful for constructors and users of single force platforms, especially those involved in posturographic assessments of asymmetric conditions such as hemiparesis.

Effects of a prior stretching of the plantarflexor muscles on the capacity to control upright stance maintenance in healthy adults.

To assess whether prior stretching of a muscle can induce improved postural control, 15 healthy adults stood still upright with their eyes closed before and after a series of bilateral stretches of the triceps surae muscles. The analysis focused on the center of pressure (CP) and the vertical projection of the center of gravity (CGv) trajectories and their difference (CP - CGv). The prolonged stretching induced a forward shift of the mean position of the CGv. The frequency analysis showed a constancy of the amplitudes of both basic movements whereas an increased mean power frequency was seen for the CP - CGv movements. A fractional Brownian motion modeling of the trajectories indicates shortest time intervals and lower covered distances by the CGv before a change in its control occurs along the antero-posterior axis. This reorganization is thought to be a result of improved body movement detection, which allows postural control over the longest time intervals to be triggered more rapidly.