Four-way-leaning test shows larger limits of stability than a circular-leaning test

Abstract

Introduction: Limits of stability (LOS) have extensive clinical and rehabilitational value yet no standard consensus on measuring LOS exists. LOS measured using a leaning or a circling protocol is commonly used in research and clinical settings, however differences in protocols and reliability problems exist.

Objective: This study measured LOS using a four-way-leaning test and a circular-leaning test to test which showed larger LOS measurements. Furthermore, number of adaptation trials needed for consistent results was assessed.

Method: Limits of stability were measured using a force plate (Metitur Good Balance System^®) sampling at 50Hz. Thirty healthy subjects completed 30 trials assessing LOS alternating between four-way-leaning test and circular-leaning test.

Results: A main effect of methods (ANOVA:F(1,28)=45.86, P<0.01) with the four-way-leaning test showing larger values than the circular-leaning test (NK, P<0.01). An interaction between method×directions was found (ANOVA:F(3, 84)=24.87, P<0.01). The four-way-leaning test showed larger LOS in anterior (NK, P<0.05), right (NK, P<0.01) and left direction (NK, P<0.01). Analysis of LOS for the four-way-leaning test showed a difference between trials (ANOVA:F(14,392)=7.81, P<0.01). Differences were found between trial 1 and 7 (NK, P<0.03), trial 6 and 8 (NK, P<0.02) and trial 7 and 15 (NK, P<0.02). Four-way-leaning test showed high correlation (ICC>0.87) between first and second trial for all directions.

Conclusion: Four-way-leaning test yields larger LOS in anterior, right and left direction making it more reliable when measuring LOS. A learning effect was found up to the 8th trial, which suggests using 8 adaptation trials before reliable LOS is measured.

Keywords: Adaptation trials; Center of pressure; Limits of stability; Method comparison; Postural control.