Biomechanical Response to External Biofeedback During Functional Tasks in Individuals With Chronic Ankle Instability

Abstract

Context: Altered biomechanics displayed by individuals with chronic ankle instability (CAI) is a possible cause of recurring injuries and posttraumatic osteoarthritis. Current interventions are unable to modify aberrant biomechanics, leading to research efforts to determine if real-time external biofeedback can result in changes.

Objective: To determine the real-time effects of visual and auditory biofeedback on functional-task biomechanics in individuals with CAI.

Design: Crossover study.

Setting: Laboratory.

Patients or other participants: Nineteen physically active adults with CAI (7 men, 12 women; age = 23.95 ± 5.52 years, height = 168.87 ± 6.94 cm, mass = 74.74 ± 15.41 kg).

Intervention(s): Participants randomly performed single-limb static balance, step downs, lateral hops, and forward lunges during a baseline and 2 biofeedback conditions. Visual biofeedback was given through a crossline laser secured to the dorsum of the foot. Auditory biofeedback was given through a pressure sensor placed under the lateral foot and connected to a buzzer that elicited a noise when pressure exceeded the set threshold. Cues provided during the biofeedback conditions were used to promote proper biomechanics during each task.

Main outcome measure(s): We measured the location of center-of-pressure (COP) data points during balance with eyes open and eyes closed for each condition. Plantar pressure in the lateral column of the foot during functional tasks was extracted. Secondary outcomes of interest were COP area and velocity, time to boundary during static balance, and additional plantar-pressure measures.

Results: Both biofeedback conditions reduced COP in the anterolateral quadrant while increasing COP in the posteromedial quadrant of the foot during eyes-open balance. Visual biofeedback increased lateral heel pressure and the lateral heel and midfoot pressure-time integral during hops. The auditory condition produced similar changes during the eyes-closed trials. Auditory biofeedback increased heel pressure during step downs and decreased the lateral forefoot pressure-time integral during lunges.

Conclusions: Real-time improvements in balance strategies were observed during both external biofeedback conditions. Visual and auditory biofeedback appeared to effectively moderate different functional-task biomechanics.

Keywords: ankle sprains; balance; external focus of attention.

Figure 1

A, The crossline laser (Calpac Lasers) powered by 2 AA batteries. B, Participant setup with both visual- and auditory-biofeedback devices. C, For the auditory device, a pressure sensor was placed inside laboratory shoes (model M680V3; New Balance Inc). The sensor was connected to a potentiometer (Tekscan, Inc) powered by a 9-V battery and attached to a buzzer.

Figure 2

Percentage of pressure data points in each quadrant during the eyes-open static balance trial in the baseline and visual- and auditory-biofeedback conditions. ^a Indicates difference from baseline (P ≤ .05). Abbreviations: AL, anterolateral; AM, anteromedial; PL, posterolateral; PM, posteromedial.