BACKGROUND: Limited research exists on the effects of both high and low frequency whole body vibration (WBV) on individuals with subacute lateral ankle sprains. HYPOTHESIS/PURPOSE: To examine the difference in the effects of high and low frequency WBV on limits of stability (LOS) in adults with a subacute ankle sprain. It was hypothesized that WBV would improve effects on outcome variables for LOS as a component of dynamic balance. STUDY DESIGN: Quasi-experimental, pretest-posttest design. METHODS: Fifteen participants ages 19 to 27 years (mean age 22 +/- 2.36) with either a grade I or grade II lateral ankle sprain received WBV in bilateral stance under three randomized conditions (high frequency 25 Hz, low frequency 6 Hz, and control, which consisted of bilateral stance with machine off) for six minutes over three sessions (one time per week). The LOS test, consisting of 5 variables, were assessed using the NeuroCom Balance Manager-SMART EquiTest (Natus Medical Incorporated, Pleasanton, CA) at baseline and after the intervention period. The participants completed a practice LOS test and then had a six-minute standing rest break. After the rest break, they completed the pre-LOS (baseline) test. Intervention was administered using the Galileo R Med L Chip Research (Novotec Medical GmbH, Pforzheim, Germany) for six minutes for the appropriate condition of either high or low frequency WBV or control. Data analysis was performed using 2-way (2x3) repeated measures ANOVAs with additional post hoc testing as needed. RESULTS: Significant interactions were found for reaction time (RT), movement velocity (MVL), and maximal excursion (MXE) composite scores with a decrease in RT of 0.117 seconds (p = 0.022) between control and high frequency conditions during the post LOS. For composite MVL, an increase of 0.547 degrees/second (p = 0.002) between pre- and post-high frequency WBV occurred. For composite MXE, an increase of 2.13% p = 0.031 (when comparing pre- and post-high frequency WBV. CONCLUSION: Findings suggest that a single session of high frequency WBV in individuals with a subacute lateral ankle sprain may result in improvement in several components of postural stability. WBV is a quick intervention that could be implemented in physical therapy clinics, athletic training rooms, and workout facilities to improve an individual's LOS as a component of dynamic balance one to eight weeks post lateral ankle sprain. LEVEL OF EVIDENCE: 2b.

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