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Balance control and muscle activity in various unstable shoes compared to barefoot during one-leg standing

The purpose of this study was to compare muscle activity and balance control of young healthy subjects during one-leg standing using various unstable shoes, a stable reference running shoe and barefoot condition. Twenty athletic female subjects participated in this study. The protocol consisted of quiet one-leg standing measured in six randomized conditions: four different unstable shoes, reference shoe and barefoot. The data were measured using the Pedar-X® insole system and a surface electromyography (EMG) system. Activity of eight muscles of the right leg was measured and integrated EMG (IEMG) and root mean square (RMS) values were calculated. For the balance control analysis, centre of pressure (CoP) total, medial–lateral and anterior–posterior excursions were calculated. A descriptive analysis and also one-way repeated-measures ANOVA (α = 0.05) and post-hoc tests were performed. The results indicate larger CoP total excursion as well as CoP medial–lateral excursion in barefoot compared to all shoe conditions (p < 0.05), whereas no differences were observed within the shoe conditions. Higher muscle activity (IEMG) was identified for the lateral gastrocnemius, vastus medialis and rectus femoris during barefoot standing with no difference between shoe conditions. No differences in RMS values could be observed for all analysed conditions. In conclusion, this study could not find any relevant differences between the shoe conditions for any of the analysed variables. Surprisingly, the barefoot condition showed the greatest instability (CoP excursions) and the highest muscle activity compared to all shoes analysed in the study. Further studies with unstable shoes are needed to investigate their instability effects.