Concurrent validity and discriminative ability of force plate measures of balance during the sub-acute stage of stroke recovery

Background: Many objective measures of balance control, including force plate measures of standing balance, lack sufficient validation for use in the stroke population. Research questions: Do force plate measures of quiet standing balance during the sub-acute stage of stroke recovery have concurrent validity (i.e., correlate with functional balance measures) and discriminative ability (i.e., differentiate fallers from non-fallers and/or those with low-moderate versus high risk of falling)? Methods: Participants completed one trial of quiet standing with eyes open, lasting for 30 seconds. History of falls was identified retrospectively, based on falls during the acute-care stay. Risk of falling was determined at admission to inpatient rehabilitation using the STRATIFY scale. Mean speeds of centre of pressure along the anterior-posterior and medial-lateral axes, weight-bearing asymmetry, and symmetry index were calculated. Concurrent validity of these measures were quantified against the Berg Balance Scale; their abilities in differentiating fallers from non-fallers, and individuals with low-moderate versus high risk of falling were evaluated using the area under the receiver operating curve (AUC). Results: Among the measures studied, mean speeds of centre of pressure along the anterior-posterior and medial- lateral axes demonstrated moderate concurrent validity (rho=-0.490, and-0.440, respectively; p-values <= 0.002), while the other two measures did not show sufficient concurrent validity. Weight-bearing asymmetry showed some ability in differentiating fallers from non-fallers (AUC=0.67); however, other measures demonstrated negligible to no discriminative ability. Significance: Our findings suggest that speeds of centre of pressure have moderate concurrent validity to quantify balance during the sub-acute stage of stroke; they can be used to better inform rehabilitation practice about the balance ability following a stroke. Weight-bearing asymmetry has some ability to discriminate people with and without a history of falls; however, research is required to identify its ability to discriminate future fallers and non-fallers.