A method for measuring vertical forces applied to the upper limb during sit-to-stand

The aim of this study was to develop a basic measurement system to estimate the vertical loading of the upper limb during the sit-to-stand activity, with a view to increasing the understanding of the loading of the wrist in daily living activities. A chair was adapted and instrumented with strain gauges and position sensors so that the force applied through the upper limbs to the arms of the chair could be calculated. Four aspects of the chair's geometry could be varied. A force plate was positioned on the floor between the legs of the chair to record the corresponding foot loading. Twenty normal subjects (22-56 years, mean 32.7 years) participated in a pilot study in which loading through the upper and lower limbs was recorded for a range of chair geometries. The vertical force transmitted through each upper limb was typically 20-30 per cent of bodyweight. The vertical upper limb load averaged across all subjects showed a small reduction when either the seat height or the height of the chair arms was increased.