A simple and practical method for evaluating overall measurement error of joint moments obtained by a force plate and a position sensing device.

Joint moments are now widely used in the field of gait analysis and sports biomechanics. They are usually calculated from the data obtained by a force plate and a position sensing device. Although separate assessment of the measurement error of a force plate and a position sensing device is possible, it can give only the worst case estimate of the joint moments. A simple and practical method is presented here which can give an estimate of the overall error of the combined system. The basic principle of this method is that if a lumped load is applied to a point where the joint center is supposed to be located and the moment is calculated about this point, then the moment should be zero. Thus, the deviation of the calculated moment from zero will give an estimate of the overall error. Examples of experimental data of a joint moment measuring system are given to validate this method. Various factors which contribute to the overall error are discussed and a method of reducing it by software compensation is presented.