Goniometry

Goniometers are used to determine angular changes in the body joints during movements. Simple goniometers usually consist of two flexible plastic or light metal rails that are fixed to adjacent body segments connected by a joint (e.g. at the knee joint: thigh versus lower leg) using rubber bands or adhesive strips. The goniometer rails are connected to each other via smooth-running potentiometers so that angle changes in the body joint can be recorded via the potentiometer in the form of electrical voltage changes. As this form of angle measurement causes errors due to the fact that the axis of the potentiometer misses the (often wandering) joint axis and can also interfere with the movement sequence, other measurement techniques are used in more modern goniometers. We currently use goniometers from the English company Biometrics (formerly Penny & Giles) for our investigations.

This involves measuring changes in angle between the axes of the end blocks by means of a core wire with several strain gauges arranged between two small end blocks, which are fixed to adjacent body segments (see photo). If the angle between the two end blocks changes, the change in strain along the length of the wire is converted into changes in tension via an electronic measuring system, thereby determining the angle between the end blocks.