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Dynamic Postural Stability Deficits in Subjects with Self-Reported Ankle Instability


Medicine & Science in Sports & Exercise: March 2007 - Volume 39 - Issue 3 - pp 397-402
doi: 10.1249/mss.0b013e31802d3460
CLINICAL SCIENCES: Clinical Investigations

Purpose: A limited understanding of how functional ankle instability (FAI) affects dynamic postural stability exists because of a lack of reliable and valid measures. Therefore, the purpose of this investigation was to determine whether a new reliable index for dynamic postural stability could differentiate between those with stable ankles and those with FAI.

Methods: Data were collected on 108 subjects (54 subjects with stable ankles (STABLE group); 54 subjects with functionally unstable ankles (FAI group)). Subjects performed a single-leg-hop stabilization maneuver in which they stood 70 cm from the center of a force plate, jumped off both legs, touched a designated marker placed at a height equivalent to 50% of their maximum vertical leap, and landed on a single leg. The dynamic postural stability index and directional stability indices (medial/lateral, anterior/posterior, and vertical) were calculated. The raw and normalized (to energy dissipated) indices were compared between groups.

Results: Significant differences were noted for the anterior/posterior stability index (FAI = 0.36 ± 0.09, STABLE = 0.30 ± 0.06). Similar results were seen for the vertical stability index (FAI = 0.73 ± 0.17, STABLE = 0.61 ± 0.13), the normalized dynamic postural stability index (FAI = 0.85 ± 0.17, STABLE = 0.73 ± 0.12), the normalized vertical stability index (FAI = 0.007 ± 0.004, STABLE = 0.005 ± 0.001), and the dynamic postural stability index (FAI = 0.008 ± 0.003, STABLE = 0.006 ± 0.001).

Conclusions: These results indicate that the dynamic postural stability index is a sensitive measure of dynamic postural stability and is capable of detecting differences between individuals with stable ankles and individuals with functionally unstable ankles.

1Center for Exercise Science; and 2Department of Physical Therapy, University of Florida, Gainesville, FL

Address for correspondence: Erik A. Wikstrom, M.S., A.T.C., University of Florida, Department of Applied Physiology and Kinesiology, PO Box 118205 Gainesville, FL 32611-8205; E-mail:

Submitted for publication June 2006.

Accepted for publication October 2006.

©2007The American College of Sports Medicine