Analysis and decomposition of signals obtained by thigh-fixed uni-axial accelerometry during normal walking

The use of piezo-resistive uni-axial accelerometer signals in gait analysis is complicated by the fact that the measured signal is composed of differe nt types of acceleration. The aim of the study is to obtain insight into th e signal from a tangential accelerometer attached to the thigh during walki ng. Six subjects walk with three different speeds. Simultaneous measurement s are performed with accelerometers, footswitches and an opto-electronic sy stem. The components of the accelerometer signal are calculated from the op to-electronic system. A clear relationship is found between the measured an d calculated accelerometer signals (range RMS: 0.76-3.69 m s(-2), range rms : 0.22-0.61). The most pronounced feature is a high positive acceleration p eak (> 10m.s(-2)) at the end of the cycle. The gravitational acceleration d uring one cycle is characterised by a sinusoidal shape, whereas the inertia l acceleration contains higher-frequency components (up to 20 Hz). During t he major part of the gait cycle, the gravitational and inertial acceleratio n make opposing contributions to the signal. As a result, the gravitational acceleration influences the amplitudes of the measured acceleration signal , the shape and peaks of which are mainly determined by the inertial accele ration. Because the gravitational and inertial accelerations differ in freq uency components, the application for gait analysis remains feasible.