Optimum position and orientation of handrail for sit-to-stand movement

Abstract

The sit-to-stand (STS) movement is performed throughout the day, and providing handrails is one method of making the STS movement easy. However, designers may have determined the installation position of handrails using intuition and trial and error. The aim of this study is to determine the optimum position and orientation of handrails by minimizing the quantified physical load of the STS movement. Twelve university students participated, and eight electromyograms (EMGs), namely, of the brachioradialis, flexor carpi ulnaris, extensor carpi radialis longus, latissimus dorsi, right and left rectus femoris, and right and left tibialis anterior, were recorded. Observations with handrails at various tilt angles and forward distances from the edge of the seat were analyzed for the optimization. The total physical load (TPL) function was formulated as the weighted sum of the EMGs. The weight coefficients were determined by maximizing the correlation coefficient between the measured subjective scores and the TPL function values. The result shows that the handrail installation position significantly affects all of the EMGs except those of the right and left rectus femoris. The weight coefficients of the TPL function are positive for the upper limb muscles, whereas they are zero for the lower limb muscles. The handrail position for multiple users was formulated to minimize the TPL function, and hence the optimum position was determined.

Keywords

• ergonomics
• optimal design
• electromyography
• handrail
• sit-to-stand movement