Postural stability in stroke patients: Vectorial expression of asymmetry, sway activity and relative sequence of reactive forces

Abstract

Bilateral force measurements on the supporting limbs in postural sway while standing still were made to evaluate post-cerebral-vascular accident (CVA) patients during rehabilitation. Normal subjects of the same age group were tested as controls. From the force tracings obtained, three oscillation frequencies were identified, with orders of magnitudes of 7, 1 and 0.1 Hz, respectively, of which the middle frequency, i.e. that corresponding to 1 Hz, was selected for subsequent processing and analysis. These included the determination of relative sequence of the force vectors on both feet and evaluation of timings and amplitudes of the waveforms. Weight-bearing imbalance was defined in the vertical direction to express the difference between the average forces supported by each of the legs. In the horizontal plane, two parameters were defined: sway total activity (SA), to represent the vector summation of the absolute values of the horizontal force components acting on both legs; and asymmetry (ASYM) to express the difference in activities between the two legs. The results presented disclose the reactive force patterns acting on each of the legs of post-CVA hemiplegic individuals, in comparison with normal individuals. Although these forces were shown to act synchronously on both legs, they appeared to be asymmetrical in nature, with a typical vectorial pattern for every individual, which generally differed from that of normal subjects. Sway activity was found to be significantly higher in hemiplegics compared with the normal controls.

Reliability and comparison of weight-bearing ability during standing tasks for individuals with chronic stroke

“…When given this choice it appears that subjects do not bear the weight that they are capable of. This trend has been observed in acute, [1][2][3][4]6 subacute, 5 and now chronic stroke survivors, although the degree of asymmetry during bilateral tasks appear to be greater in the acute stroke population. In addition, our observation is consistent with the findings that individuals with stroke can distribute their weight more symmetrically when requested to rise from a chair with their body weight distributed evenly on both feet 8 and provides further support for the undertaking of interventions to improve symmetry during functional tasks.…”

“…In fact, it has been reported that the majority of individuals (79 to 87%) with stroke bear less weight on the paretic limb (25 to 43% of body weight) during the static task of quiet standing. [1][2][3][4][5][6] Possible causes of this reduced ability following a stroke include pain, spasticity, impaired balance, sensory loss, neglect, muscle weakness, and perceptual deficits.…”

Contribution of Muscle Strength and Integration of Afferent Input to Postural Instability in Persons with Stroke

“…condition one) in postural sway when comparing persons with stroke with controls, as sway is increased after stroke even without manipulating the sensory environment. 18 Muscle strength (i.e. isokinetic, concentric joint torque) of the paretic and non-paretic ankle, knee, and hip flexors and extensors of the persons with stroke was assessed using a KinCom Isokinetic Dynamometer (Chattanooga Group Inc).…”

Does the backrest shape of the wheelchair influence the asymmetric posture of patients with hemiparesis? A single institution pilot study

“…Many patients with post-stroke hemiparesis have balance deficits and natural decreases in muscle strength and age-related endurance [3,4]. Specifically, stroke patients usually place more weight unilaterally [5,6] and find balancing when standing/ sitting difficult [7,8]. Moreover, increased postural sway worsens these balance difficulties [9].…”