Tremor measurement: a new algorithm to deal with accelerometric data in 3D

Electromyography can be used to accurately quantify the amplitude, frequency and pattern of muscular activation during tremor. Accelerometric devices in contrast, are easier to apply, but they cannot detect the pattern of muscular activation. Usually, tremor that can be measured with a 3-axis-accelerometer, is not distributed isotropically in 3D space but is aligned along a principal component. We describe a simple way to detect the main axis of the tremor in 3D measurements of tremor by using a principal component varimax transformation of the 3D data with an interactive software based on MATLAB. The magnitude of the principal tremor component is then displayed over time. Its frequency and amplitude can be analysed with established algorithms (Fourier transform). This method is appropriate for quick measurements of tremor in patient populations in which a differential diagnosis is not important. We applied this method in a large group of miners who worked with with possible environmental hazards and report our preliminary findings.