The increase in sagittal range of motion on walking in the MBT sandal in our study could be attributed to the rounded sole design of the sole of the MBT footwear. This sole design may lead to increased dorsiflexion of the ankle and subtalar joint complex at initial contact followed by an increase in plantarflexion during the propulsive phase due to the rounded anterior edge of the sole. Movement of the ankle and subtalar joint movement during stance phase would be encouraged by the rounded sole creating inertia. This could perhaps increase range of motion through the ankle and subtalar joint complex in the sagittal plane compared to walking barefoot on a flat surface and would possibly explain the results found in this study.
Furthermore, the design of the MBT shoe creates an uneven surface for the foot by using low density materials as part of the sole construction. Therefore, an increase not only in the sagittal plane movement but also frontal plane movement of the ankle and subtalar joint could be expected, and may explain our findings of a statistically significant increase in the range of motion in the frontal plane in the MBT sandal compared to walking barefoot. In this study, only the total range of frontal plane motion was measured, rather than the amount of inversion and eversion. According to Nigg et al , the rotational inversion loading was higher in an MBT shoe compared to a standard training shoe, suggesting that the increased range of frontal plane movement found in this current study may primarily be in the direction of inversion.
The results of the study demonstrated that although there was a small increase in the range of motion in the transverse plane, this difference was not statistically significant. According to Nester et al , although the ankle is often considered to have little capacity to move in the transverse plane, it is capable of considerable movement in the transverse plane (greater than 15 degrees). In our study, transverse plane range of motion varied between 7 and 57 degrees. In terms of differences between individuals, our data indicated that some subjects demonstrated a decrease in the range of motion when walking in the MBT sandal. This could have resulted from the subjects having insufficient time to get used to the shoes. Equally, some subjects reported feeling highly unstable in the shoes, which may have caused their ankle and subtalar joints to function with a higher range of motion compared to walking barefoot.
There are conflicting views on the indications for MBT footwear in the medical community and guidelines for clinicians need to be implemented so that the footwear can be appropriately prescribed. The observed increase in the range of motion at the ankle and subtalar joint complex in the MBT sandal could potentially be beneficial in certain patient groups, particularly in those where the decreased range of motion in these joints are putting strain on other parts of the musculoskeletal kinetic chain. For example, according to Monaghan et al , the therapeutic goal for chronic ankle instability is to re-train muscles to improve control during gait, and an MBT sandal may be an appropriate tool for this. However, if walking in an MBT sandal demands greater subtalar and ankle joint range of motion than is available, soft tissue damage may occur. Further research in specific patient groups needs to be conducted to aid appropriate prescription of the MBT sandal.