The quick version:

We recently completed a study evaluating the use of the Wii Balance Board to measure how asymmetrical people move before and after total joint replacement. The purpose of the study was to examine the reliability and the validity of this low-cost device as a clinical tool. We compared the Balance Board to the our expensive Motion Analysis equipment. What did we find? SPOILER ALERT: The Wii Balance Board did surprisingly well, although there were some limitations to its use. This article, “Validity of the Nintendo Wii Balance Board to assess weight bearing asymmetry during sit-to-stand and return-to-sit task” was published in the journal Gait and Posture. It is available through the PubMed here: If you are unable to access the article, please let me know!

The Detail:

Background and rationale: Movement asymmetry is common in patients with unilateral lower extremity pathology. In particular, weight bearing force asymmetry can be dramatically different between limbs, even in there is no difference in joint angles. In figure 1, you can see that in our sample of patients before and after joint replacement, there is little difference in joint angles, but dramatic differences in weight bearing force between the affected and unaffected limbs. This suggested to us that we need a way to measure force asymmetry in the clinic because visual inspection wasn’t going to tell us the full story.

Movement Asymmetry Sit to Stand

Study Methods: Thirty-five individuals before, or within 1 year of total joint arthroplasty performed a sit-to-stand and return-to-sit task in two conditions. First, subjects performed the task with both feet placed on a single WBB. Second, the task was repeated with each foot placed on an individual laboratory force plate. This protocol with and without the Balance Board can be seen in the figure below. Peak vertical ground reaction force (VGRF) under each foot and the inter-limb symmetry ratio were calculated. Validity was examined using Intraclass Correlation Coefficients (ICC), regression analysis, 95% limits of agreement and Bland-Altman plots.

sit to stand with and without Balance Board


The Results: We found that there was a very high relationship between the laboratory force plates and the Wii Balance Board. The reliability between trials was similar for the force plates and the Wii Balance Board. Below is a graph of the regression. On the X-axis is the data from the Wii Balance Board. It is either in Newtons (for force) or percentage for the symmetry index (which was calculated as the operated limb divided by the non-operated limb). The Y-axis are the same data from the force plates. You can see a very tight regression, but the slope is not 1. What does this mean? Well it means that when subjects used the Balance Board, they tended to be more symmetrical.

Regressions movement symmetry

Conclusions: The Wii Balance Board can be used to measure movement asymmetry in the clinic. However, clinicians should be aware that the raw symmetry values will be higher on the Balance Board than on the force plates. This is most likely attributed to the fact that the subject’s foot position was constrained on the Balance Board. They had to place their feet in a more symmetrical fashion on the Balance Board, but this was not required on the force plates. If anyone is interested in obtaining the program we used to get the force data from the Balance Board, just email me!


— Written by Joseph Zeni, Jr. PT, PhD

The article discussed in this post was written by Sumayeh Abujaber, PhD; Gregory Gillispie, BS; Adam Marmon, PhD, and Joseph Zeni Jr.PT, PhD. The authors acknowledged Federico Pozzi, PT, MA, for his assistance in data collection and the staff in Delaware Rehabilitation Institute for recruiting subjects. The Research Core was supported by NIH grant P30 GM103333-03. This study was supported by the National Institutes of Health (K12 HD055931, 5R01AR48212-07, and P20RR016458-10), the University of Delaware Research Foundation, and a scholarship from the University of Jordan to Dr. Abujaber.