The effect of unstable sandals on single-leg standing

Purpose: Unstable footwear lacks peer-review published research to support concepts and claims. The present study was therefore undertaken to quantify and compare the effect of commercially available unstable sandals on single-leg balance in a healthy female population. Methods: Fifteen participants stood on their right-leg in one control sandal (Earth) and four sandals that are marketed as unstable footwear (FitFlop, Masai Barefoot Technology, Reebok Easy-Tone and Skechers Tone-Ups). Centre of pressure trajectory, lower limb kinematics and lower limb muscle activation was recorded as participants undertook three 30 second trials in each sandal. Results: The unstable sandals altered parameters related to stability in participants. Namely Masai Barefoot Technology increased centre of pressure range in the anterior-posterior direction and concurrently increased sagittal ankle motion. Reebok EasyTone had a similar effect in the coronal plane at the ankle. Muscle activation increased in the unstable sandals, with significant differences apparent in the medial gastrocnemius, soleus and rectus femoris, predominantly in Masai Barefoot Technology. Findings were attributed to the large rocker sole on the Masai Barefoot Technology sandal and more subtle outsole designs in the other sandals. Conclusions: Overall minimal differences from the control sandal were evident and it is expected that dynamic tasks may elicit greater differences in stability. The instability imposed by the sandals is design-specific and consideration should be given to this when the footwear is recommended to specific individuals