Effects of footrest heights on muscle fatigue, kinematics, and kinetics during prolonged standing work

Background: Among the tools for relieving lower back pain, footrests are commonly recommended. Few studies have investigated the effects of footrest and the proper application of footrest height. Objective: The purpose of this study was to compare the effects of the normalized footrest height on muscle fatigue, kinematics, kinetics, and pain intensity. Methods: In total, 13 males who had a history of non-specific lower back pain during prolonged standing were recruited. The experimental conditions were 2-hour prolonged standing with no footrest and with footrests of 5%, 10%, and 15% of body height. Muscle fatigue was investigated through measurements of the median frequency ratio and the muscle activity ratio (post/pre) in lumbar erector spinae. The lumbo-pelvic angles, and the external moment in the lumbar region were investigated. A visual analog scale was used to investigate the intensity of the pain. Results: The footrests at 10% and 15% of the body height caused a lower change in the median frequency ratio and the muscle activity ratio than the other conditions. The footrest at 10% of the body height placed the lowest external moment on the lumbar region among all the conditions. The pain intensity was significantly lower in with footrest conditions than with no footrest condition. Conclusions: The results suggests that a footrest height of 10% of the body height can be recommended as a normalized height for prolonged standing work in subjects with a history of non-specific lower back pain during prolonged standing.