Unstable footwear designs have been widely studied and implemented over the last decade as training devices to strengthen muscles and train  human neuromuscular control during casual daily activities. It is well known that the use of unstable footwear designs alters gait kinematics and kinetics, activation patterns of the lower-limb musculature, and loading patterns of the foot. However, previous studies include contflicting findings regarding the exact effect of unstable footwear on gait patterns and balance control strategies. This study was therefore, designed to reveal unanswered questions regarding the influence of unstable footwear on gait patterns and the neuromuscular control system, using familiar gait-lab analysis methods, combined with, advanced methods in Electroencephalographic (EEG) data recordings and signal analysis.

Three experiments were conducted utilizing a foot-worn biomechanical device, calibrated to both stable and unstable footwear configurations. In the first experiment, the effect of unstable vs. stable footwear configurations on gait kinematics and kinetics was investigated. Comparison revealed a significant decrease in variability of frontal-plane foot center of pressure (COP), transverse-plane ankle moment, and frontal-plane shoulder angle while walking in the unstable configuration. while transverse-plane spine angle variability increased. This may reflect a compensatory mechanism to maintain both stability and adaptability, specific to the unstable shoe construction investigated in  the present study. In the second experiment, we investigated the effect of unstable footwear on COP and Electromyography (EMG) during and after 20 minutes. Comparison between both configurations revealed an increase in muscle activity, decrease in COP variability and a medial shift in its location with unstable vs. stable footwear configurations. Results after training were affected in the same direction as with the training with a negative association in time, suggesting that once the participants adapted a new pattern during the training, they did not retrieve to their prior gait patterns immediately, when measured with the stable shoe. Instead, changes in gait patterns had after effects that remained for approximately 30 minutes after the training. This pattern brings to light the existence of a deeper neuro-muscular connection, that is continuously affecting the movement as was observed in the third experiment, at which we have investigated the cortical-muscular coherence (CMC) between EEG and EMG signals from the Tibialis-anterior muscle (TA) during gait on a treadmill with stable and unstable footwear designs. Our findings revealed that CMC values were significant during loading response, early and late swing with both shoe configurations, however and additional CMC appeared with the unstable shoe configuration, prior to heel-strike of the contralateral limb which probably emphasizes the importance of corticospinal control for maintaining stability. 

In conclusion, the findings of the proposed research identify a specific and unique biomechanical and neurophysiological mechanisms that are important for understanding cortical control of human gait and propose new insights for future investigations of motor control strategies with unstable footwear designs that could have substantial implications in the design and use of unstable training devices.