Comparison of force output and muscle EMG during use when using a sit/stand stool versus standing

Abstract

Sit/stand stools are often recommended for workers that exhibit lower leg strain or report pain in the legs and feet. This study was conducted to determine if workers are able to produce the same level of hand and arm force while using a sit/stand stool as while standing. Sixteen right-handed, male college students participated in this study. The forearm flexor and extensor muscle activity was monitored using surface electromyography (EMG) during static maximal exertions as well as the force output via a screwdriver attached to a load cell. Force output and the ratio of the EMG activity to force ratio was calculated for the dependent variables. The independent variables were orientation of the screwdriver (horizontal plane vs. vertical plane), body position (leaning against a sit/stand stool vs. standing), muscle (forearm flexors vs. forearm extensors) and trial (three exertions of each combination of body position and screwdriver position); the subject variable was used as the error term in the ANOVA calculations and all combinations were sequenced in a Latin Square design. The results indicated that only the screwdriver position had a significant effect upon the generated maximal force. For the EMG to force ratio where muscle was used as an independent variable, only the interaction between the muscle group and screwdriver position was significant. The use of the sit/stand stool had no significant effect on either maximal force output or on the EMG/force ratio indicating that the use of a sit/stand stool to alleviate leg stress does not effect the work output of the upper limb for tasks similar to the ones described in this study.