The transfer of weight onto a limb is essential for functional mobility, and is a requirement for rising from a chair, transfers, walking, turning and stair climbing. Reduced ability to weight-bear on the paretic limb is recognized as a common impairment following a cerebrovascular accident. 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.1–6
Possible causes of this reduced ability following a stroke include pain, spasticity, impaired balance, sensory loss, neglect, muscle weakness, and perceptual deficits.
Reduced ability to weight-bear on the paretic limb is not limited to static standing tasks. Weight-bearing during dynamic tasks such as rising from a chair7–9
or voluntarily weight-shifting to one limb while standing10–13
is also compromised following a stroke. Asymmetrical weight-bearing has been reported when rising from a chair, with the paretic limb accepting between 25 to 38% of body weight.7–9,14
In addition, it has been reported that individuals with stroke can only shift approximately 55% of their body weight onto the paretic limb while standing in the forward direction in a step stance posture and 65% in the lateral direction with feet parallel.13
In contrast, healthy elderly individuals have demonstrated the ability to voluntarily shift 95% of their body weight onto a single limb in both the forward and lateral directions.13
Weight-bearing ability correlates with functional performance in individuals with stroke. The degree of weight-bearing asymmetry during quiet standing has been correlated to motor function, level of self-care independence as well as length of hospital stay following stroke.4,15
The ability to transfer body weight laterally or forward onto the paretic limb while standing has been shown to be indicative of walking performance.13,14,16
Cheng et al.14
suggested that the asymmetrical body weight distribution during a rise from a chair might be a contributing factor to the cause of falls in individuals with stroke. In addition, increased weight-bearing abilities have been shown to improve the ability to rise from a chair and bilateral symmetry.6,17
Although a major focus of rehabilitation is to increase the tolerance and ability to bear weight on the paretic limb during various functional tasks,18,19
there has been no study that has examined the test-retest reliability of weight-bearing ability across sessions in individuals with stroke. Goldie et al.13
reported high within session reliability (consecutive trials) for forward and lateral weight-shifting while standing for individuals with stroke, however, the day-to-day variability is not known. Reliability is the degree to which measurements are free from error20
and is a pre-requisite prior to use as an outcome measure. More specifically, the test-retest reliability is important to evaluate for rehabilitation since outcome measures are generally evaluated over time to assess the effectiveness of treatment interventions. It is imperative that clinicians know how much of a measurement change can be attributed to random variation and how much is due to true change. Therefore, the first purpose of this study was to determine whether the weight-bearing ability during functional tasks measured across two separate days as quantified by the vertical ground reaction force is reliable for the paretic and non-paretic limbs in individuals with stroke.
Weight-bearing activities are often assessed or practiced in various standing postures (e.g., step stance versus feet parallel), into different directions (lateral, forward, backward) and under static and dynamic conditions. There is little information as to how the particular task, direction or posture affects the magnitude of weight-bearing or how the weight-bearing performance among different tasks relates to one another. Thus, the second purpose of this study was to a) compare the magnitude of weight-bearing ability among five functional standing tasks (quiet standing, rising from a chair, weight-shifting in a forward, lateral and backward direction), and b) measure the relationship (i.e., correlation) of the weight-bearing ability among the five tasks.
There is also growing evidence that motor function is not normal on the non-paretic side in individuals with stroke, as evident by the presence of muscle weakness21–22
and altered motor coordination23
on this side. Goldie et al.13
reported that individuals with stroke could not weight-shift in a lateral or forward direction onto their non-paretic limb as well as healthy elderly subjects. Thus, the non-paretic, in addition to the paretic limb was evaluated in this study.