An unstable shoe was developed as a walking device to strengthen the lower extremity muscles and reduce joint loading. A large number of studies have reported higher electromyographic (EMG) activity throughout the gait cycle in most of the lower limb muscles, and significant kinematic changes in the lower extremity. However, no studies have examined the effects of wearing unstable shoes on spine kinematics and trunk muscle activity during gait. To compare trunk muscle activity and lumbar spine range of motion (ROM) during gait using an unstable shoe and a conventional stable control shoe. Participants underwent gait analysis while simultaneously collecting surface EMG data of erector spinae (ES) and rectus abdominis (RA) and lumbar spine sagittal plane ROM while treadmill walking wearing regular shoes and unstable shoes. The resultsts exhibited that the unstable shoes resulted in significantly higher ES and RA EMG muscle activity levels in all gait phases compared to control shoes (p<0.001). In addition, the unstable shoe condition displayed a significantly higher mean (mean difference: 3.1º; 95% CI 2.2º to 4º) and maximum (mean difference: 4.5º; 95% CI 2.6º to 6.5º) lumbar spine extension values (p<.001).
This study found that unstable shoes result in greater trunk muscle activity (ES, RA) and lumbar lordosis during gait compared to control shoes.