Standing on one leg is an essential task in activities of daily living (ADLs), from walking to stair climbing, shower transfer and lower body dressing (while standing). Besides that, it is necessary in many occupational and sports activities, making it an important stance to be included within a balance assessment session. One-leg stance duration is one the oldest balance tests using a simple stopwatch .
In PhysioSensing Balance software there is a similar test named Unilateral Stance, which allows the assessment of the patient’s postural control with left and right foot raised, alternately, enhancing the standard one leg test with objective quantification of sway.
How is it done?
This protocol measures balance in four conditions:
- Stand on the left leg with eyes open.
- Stand on the left leg with eyes closed.
- Stand on the right leg with eyes open.
- Stand on the right leg with eyes closed.
Figure 1 – Interface of Unilateral Stance protocol, for left and right foot, respectively.
The patient must try to maintain the position for 10 seconds with hands on hips. Each condition has three trials. During each test legs should not touch each other.
After performing all the conditions of the protocol, the values of the sway velocity for each condition appear. The sway velocity is the displacement of the center of pressure during the trial divided by the time (°/s). This concept can be observed in Figure 2, which illustrates the variation of COP (sway displacement) during each acquisition (100 acquisitions per second), allowing the calculation of the COP sway velocity in degrees per second.
Figure 2 – The body sway can be translated into center of pressure values in the mediolateral and anteroposterior directions (statokinesigram), and the software posteriorly analyzes the COP displacement (ΔDn) during the trial to calculate the mean COP sway velocity (°/s).
The software also evaluates the sway velocity difference (in percentage) between the left and right side with the eyes opened and closed. The bar points to the side with better performance. These values are presented along with the normative data for the patient age (Figure 3). In addition, the center of pressure trace for each condition can be observed (Figure 4).
Figure 3 – Example of the results section graphs.
Figure 4 – Example of the COP trace during the US protocol for the first two conditions. All this information can be quickly exported to a PDF report, and also view the progress between evaluations. This allows a more objective and quantitative look at the patient’s performance during one leg standing tasks, enhancing the observational testing of single leg stance.
This protocol measures the functional ability while standing on one leg, in which several factors can influence a patient’s performance on this stance. Results outside the normative values or a fall in one leg is a sensitive indicator of motor impairment, but it does not provide information about the nature of it. Possible causes include musculoskeletal problems (such as leg weakness), neuromuscular problems (e.g., Parkinson’s disease) or sensory impairments (e.g., somatosensory deficit). These patients generally have difficulty in activities that require one-leg standing. Healthy individuals have higher sway and difficulty when standing on one leg. Sway and postural instability increase with eyes closed, as the patient needs to compensate for the visual sense absence.
Bouche, K. et al.  used this protocol to investigate static balance control differences between asymptomatic and symptomatic lumbar discectomy patients and healthy individuals. They found that postural sway during unilateral stance is influenced by age, pain presence and side with former disc herniation. Also, Fjeldstad et al. demonstrated that postural stability is compromised in multiple sclerosis (MS) patients, despite minimal clinical disability, with significant differences between the MS group and healthy controls in unilateral stance (right leg) with eyes open and closed.
In addition, there are several studies about the correlation of fall risk and single-leg stance, as detailed in the systematic review by Kozinc, Z. et al. , in which several COP parameters (including sway velocity) were analysed. Other study  used the US protocol to help predict susceptibility to ankle sprain injury of high school basketball players, where subjects who had had higher preseason sway composite scores (poor balance) had almost seven times more ankle sprains.
It is also important to point out that balance assessment using the Unilateral Stance protocol allows objective measurement, that is reproducible, practical, and reliable, allowing comparison and progress monitoring after rehabilitation.
You may also like read about 12 Protocols for Balance Assessment with force/pressure plate.
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 K. Bouche, V. Stevens, D. Cambier, J. Caemaert, and L. Danneels, “Comparison of postural control in unilateral stance between healthy controls and lumbar discectomy patients with and without pain,” Eur Spine J, vol. 15, no. 4, pp. 423–432, Apr. 2006, doi: 10.1007/s00586-005-1013-4.
 C. Fjeldstad, G. Pardo, D. Bemben, and M. Bemben, “Decreased postural balance in multiple sclerosis patients with low disability,” Int J Rehabil Res, vol. 34, no. 1, pp. 53–58, Mar. 2011, doi: 10.1097/MRR.0b013e32833d6ccb.
 Ž. Kozinc, S. Löfler, C. Hofer, U. Carraro, and N. Šarabon, “Diagnostic Balance Tests for Assessing Risk of Falls and Distinguishing Older Adult Fallers and Non-Fallers: A Systematic Review with Meta-Analysis,” Diagnostics (Basel), vol. 10, no. 9, p. E667, Sep. 2020, doi: 10.3390/diagnostics10090667.
 T. A. McGuine, J. J. Greene, T. Best, and G. Leverson, “Balance As a Predictor of Ankle Injuries in High School Basketball Players:,” Clinical Journal of Sport Medicine, vol. 10, no. 4, pp. 239–244, Oct. 2000, doi: 10.1097/00042752-200010000-00003.