Response to Tendon Vibration Questions the Underlying Rationale of Proprioceptive Training

Abstract

Context: Proprioceptive training on compliant surfaces is used to rehabilitate and prevent ankle sprains. The ability to improve proprioceptive function via such training has been questioned. Achilles tendon vibration is used in motor-control research as a form of proprioceptive stimulus. Using measures of postural steadiness with nonlinear measures to elucidate control mechanisms, tendon vibration can be applied to investigate the underlying rationale of proprioceptive training.

Objective: To test whether the effect of vibration on young adults' postural control depended on the support surface.

Design: Descriptive laboratory study.

Setting: Research laboratory.

Patients or other participants: Thirty healthy adults and 10 adults with chronic ankle instability (CAI; age range = 18-40 years).

Intervention(s): With eyes open, participants stood in bilateral stance on a rigid plate (floor), memory foam, and a Both Sides Up (BOSU) ball covering a force platform. We applied bilateral Achilles tendon vibration for the middle 20 seconds in a series of 60-second trials and analyzed participants' responses from previbration to vibration (pre-vib) and from vibration to postvibration (vib-post).

Main outcome measure(s): We calculated anterior-posterior excursion of the center of pressure and complexity index derived from the area under multiscale entropy curves.

Results: The excursion response to vibration differed by surface, as indicated by a significant interaction of P < .001 for the healthy group at both time points and for the CAI group vib-post. Although both groups demonstrated increased excursion from pre-vib and from vib-post, a decrease was observed on the BOSU. The complexity response to vibration differed by surface for the healthy group (pre-vib, P < .001). The pattern for the CAI group was similar but not significant. Complexity changes vib-post were the same on all surfaces for both groups.

Conclusions: Participants reacted less to ankle vibration when standing on the BOSU as compared with the floor, suggesting that proprioceptive training may not be occurring. Different balance-training paradigms to target proprioception, including tendon vibration, should be explored.

Keywords: BOSU; ankle sprain; balance; chronic ankle instability; foam; postural control.

Figures

Figure 1.

Three plots produced by our custom LabVIEW analysis program (National Instruments, Austin, TX) from a single trial of 1 participant. Data reflect anterior-posterior sway amplitude (mm; vertical axis) in response to vibration over time in seconds when the participant was standing on the A, floor, B, foam, or C, Both Sides Up Balance Trainer (BOSU; Hedstrom Fitness, Ashland, OH). Dashed longitudinal lines indicate onset (first vertical line) and termination (second vertical line) of the vibration stimulus. Note the peak in displacement immediately after the termination of vibration when the participant was standing on floor or foam. Also note an overall decrease in displacement postvibration on the BOSU.

Figure 2.

Maximal anterior-posterior excursion (mm; vertical axis) as a function of time in seconds previbration (PRE) and during (VIB) and after vibration (POST) across surfaces for A, healthy young adults and B, adults with chronic ankle instability (CAI). Error bars represent standard error of the mean. The HEALTHY group responded with an increase in excursion from PRE to VIB and from VIB to POST while standing on the floor, an increase of less magnitude while standing on the foam, and a decrease while standing on the Both Sides Up Balance Trainer (BOSU; Hedstrom Fitness, Ashland, OH). The CAI group demonstrated an increase in excursion from PRE to VIB and from VIB to POST while standing on the floor, a decrease in excursion PRE to VIB while standing on the foam, and a minimal response to vibration from PRE to VIB while standing on the BOSU with a decrease in excursion POST.

Figure 3.

Sample entropy in the anterior-posterior direction as a function of scale factor and 3 time periods (previbration, vibration, and postvibration) across surfaces for A, healthy young adults and C, adults with chronic ankle instability (CAI). Error bars represent standard error of the mean. Note higher complexity on the Both Sides Up Balance Trainer (BOSU; Hedstrom Fitness, Ashland, OH) with no difference between the floor and foam (overlapping lines) previbration. Increased complexity with vibration is greater on the BOSU and foam compared with the floor. Decreased complexity postvibration is similar on all 3 surfaces. The light gray line represents the results when the data points were randomly shuffled. Shuffled values were about twice as high and are therefore presented on a secondary axis (right vertical axis). The area under the sample entropy curve is expressed as the complexity index. The complexity index in the anterior-posterior plane (vertical axis) is presented as a function of time (previbration, vibration, and postvibration) across surfaces for the B, healthy, and D, CAI groups. Error bars represent standard error of the mean and indicate that the variation was larger in the CAI group.