Immediate effects of unstable shoe on myoelectric activity level of selected trunk muscles during load lifting

Unstable shoes usually are used in work environments to reduce work-related disorders. The purpose of this study was to investigate the immediate effects of using unstable shoes on the activity of trunk muscles during load lifting. Material and Methods: This semi-experimental study included 15 able-bodied men. Activation of rectus abdominis, external oblique, internal oblique, multifidus, erector spinae, latissimus dorsi, quadratus lumborum, and gluteus medius muscles in the dominant side of the body was recorded during load lifting in barefoot condition and with typical shoes, and unstable shoes on. We used analysis of variance with repeated measure test for data analysis (α=0.05).

The results of this study showed significant decrease in the mean normalized muscle activation of the rectus abdominis, internal oblique, and quadratus lumborum during load lifting and also decreased normalized peak muscle activation of the rectus abdominis, quadratus lumborum, and erector spinae as well as an increase in the normalized peak muscle activation of multifidus with unstable shoes on (P<0.05). Morover, with unstable shoes on, we found significant increases in the mean frequency values of external oblique, internal oblique, multifidus, and erector spinae muscles, compared to barefoot condition and with typical shoes on (P<0.05). Also, use of unstable shoes compared to the two other conditions decreased co-contraction level of the rectus abdominis/ erector spinae, rectus abdominis/ multifidus, internal oblique/ erector spinae, and external oblique/ multifidus muscles (P<0.05).

Considering decreased activation and co-contraction levels of the selected trunk muscles use of unstable shoes may have some beneficial effects such as reduction of stress on the lumbar vertebrae and prevention of various injuries to the lumbar region such as low back pain. However, more investigations are needed in order to provide more precise results.