Effects of a new unstable sandal construction on measures of postural control and muscle activity in women

BACKGROUND: It is well established that unstable shoe constructions with rounded soles have the potential to induce acute and long-term effects on muscle activity during standing and walking. However, it is unresolved whether functional footwear with regularly shaped soles may have similar effects. OBJECTIVE: Thus, the objective of this study was to compare measures of postural control and muscle activity during quiet standing and locomotion for women using a new sandal construction with an unstable element integrated into the sole of the shoe (Biodyn sandal), a conventional stable control sandal, and a barefoot condition. METHODS: Twenty-two healthy women between the ages of 30 and 50 years participated in this study. During standing, sway area was analysed in monopedal and bipedal stance by means of a computerised balance platform. During walking, temporal and spatial stride-to-stride variability was determined using a pressure-sensitive treadmill. Surface electromyography data of lower leg muscles was simultaneously collected during stance and walk tests. RESULTS: With the Biodyn sandal, significantly larger sway area during bipedal stance (p <.05) and greater step width variability during walking (p <.01) were observed compared to the barefoot condition. During standing and walking, higher activity of muscles encompassing the ankle joint was found for the Biodyn sandal compared to the control sandal (all p <=.05). CONCLUSIONS: The Biodyn sandal produced postural instability during standing and walking which was associated with higher lower extremity muscle activations. These findings suggest that standing and walking in the Biodyn sandal could have implications for both challenging the postural control system during activities of daily living, as well as strengthening and conditioning lower extremity muscles.