Effects of unstable shoes on trunk muscle activity in patients with chronic low back pain

Unstable shoes were developed as a walking device to strengthen the lower extremity muscles and reduce joint loading. Many studies have reported increased muscle activity throughout the gait cycle in most of the lower limb muscles in healthy adults using these shoes. However, no previous studies have explored the effects of wearing unstable shoes on trunk muscle activity in patients with chronic low back pain (CLBP). Therefore, the aim of the present study was to compare the activity of selected trunk muscles in patients with CLBP during a gait test while walking wearing unstable shoes or conventional flat shoes (control).

Thirty-five CLBP patients (51.1 ± 12.4 y; 26 ± 3.8 kg/m2; 9.3 ± 5.2 Roland Morris Disability Questionnaire score) were recruited from the Orthopedic Surgery Service at the Hospital to participate in this cross-sectional study. All the participants underwent gait analysis by simultaneously collecting surface electromyography (EMG) data from erector spinae (ES), rectus abdominis (RA), obliquus internus (OI), and obliquus externus (OE) muscles, while walking on a treadmill with flat control shoes or experimental unstable shoes.

The results showed significantly higher %EMG activity in the ES (mean difference: 1.8%; 95% CI: 1.3-2.2), RA (mean difference: 1.5%; 95% CI: 0.3-2.7), and OI (mean difference: 1.5%; 95% CI: 0.2-2.8) in the unstable versus the flat-shoe condition, with a large effect size for the ES (Cohen's d = 1.27).

Based on these findings, the use of unstable shoes may be implicated in promoting spine stability, particularly in improving neuromuscular control of the trunk muscles in CLBP treatment.