Background and Purpose-It is unknown whether hemiparetic individuals are aware of their weight-bearing asymmetry during sit-to-stand tasks. This study compared the error between hemiparetic and healthy individuals' perception of weight-bearing and their actual weight-bearing distribution during the sit-to-stand task and analyzed the association between the knee extensor muscle strength and the weight-bearing distribution and perception. Methods-Nineteen unilateral hemiparetic subjects and 15 healthy individuals participated in the study. They performed the sit-to-stand transfer on force platforms under different foot placements (spontaneous and symmetrical) and had to rate their perceived weight-bearing distribution at the lower limbs on a visual analog scale. The strength of the knee extensors was assessed with a Biodex dynamometer. Results-The hemiparetic individuals presented greater weight-bearing asymmetry and errors of perception than the healthy individuals. Although no significant association was found between strength and weight-bearing perception, moderate associations were found between strength and weight-bearing distribution for both the spontaneous (rϭ0.75, PϽ0.01) and symmetrical (rϭ0.71, PϽ0.01) foot position conditions. Conclusions-This study revealed that individuals with hemiparesis after a stroke do not perceive themselves as asymmetrical when executing the sit-to-stand transfer and that the knee extensor strength is a factor linked to their weight-bearing asymmetry, not to their perception. (Stroke. 2010;41:1704-1708.)

Joint contractures are the second major impairment affecting the locomotor system of children with Duchenne muscular dystrophy (DMD). While the negative influence of joint contractures has been documented, the passive moments produced by joint contractures could benefit the gait of patients with muscle weakness. We describe a biomechanical model that quantifies the mechanical contribution of ankle and hip flexion contractures to the gait of DMD children. Kinematic and kinetic parameters were measured under the same experimental conditions during the gait and passive resistance assessment of two subjects: one healthy child as a control, and one child with DMD. The child with DMD had a plantar flexion contracture and a greater ankle stiffness coefficient than the control child. During gait, the contribution of the ankle passive moment to the net moment was more important for the child with DMD than for the control child. At the hip, passive joint moments and passive moment contribution were more important for the control child but this was not related to the presence of hip flexion contracture. These preliminary results suggest the model might be used to evaluate contractures effect on a larger cohort of subjects.

This paper describes the design, technical characteristics and first results of an adjustable instrumented chair with a sitting surface that records the forces under each thigh. The seat includes a force platform assembly suitable for measuring the magnitude, position and direction of the force applied to each thigh while sitting or rising from the chair. The natural frequency of the chair fixed to the floor was found to be 14.0 +/- 2 Hz with an estimated damping of xi = 0.20. Static tests showed that the maximal errors were 2% of the full-scale output (726 N vertically, 164 N horizontally) for both vertical and horizontal forces. The root mean square error of the center of pressure location was estimated as 5 mm. Preliminary data on the net joint moment at the hips of one healthy subject computed with and without consideration for the forces under the thighs revealed significant amplitude differences. In conclusion, the results indicate that the characteristics of the instrumented chair are acceptable and the chair can be used to assess the biomechanics of sitting and sit-to-stand and stand-to-sit tasks in various subject populations.

The objectives were to assess whether individuals who are poststroke can rate their perceived knee effort distribution during sit-to-stand tasks in various foot positions, to quantify their errors of perception and to compare these to their errors in weight-bearing perception. Weight-bearing distribution was assessed in hemiparetic participants (N = 19) using a force platform. Electromyographic (EMG) data normalized to maximal EMG values were used to quantify knee effort distribution. The difference between participants' real weight bearing and knee effort and the perceived values rated on a visual analog scale defined their errors of weight-bearing and effort perception. The perception of effort and weight bearing, and the errors therein, were compared among the four foot positions. Participants perceived only the changes induced by the different foot positions on their weightbearing distribution, not on their knee effort distribution, and they made greater perception errors with the knee effort distribution than with the weight-bearing distribution.