Determination of rotational kinematics of the lower leg during sprint running using accelerometers

Motion analysis systems measure and calculate the position of markers fixed to the body but generally restrict measurement to the laboratory environment. In contrast, inertial measurement devices are small, lightweight and self-contained and data collection is not restricted to a laboratory. Most research using inertial measurement in human locomotion studies has focused on walking. This paper describes a wireless accelerometer-based method for measuring shank angular velocity during sprint running. The system consists of body-mounted electronics with a wireless connection to a PC programmed with the necessary equations to interpret the acceleration data. The hardware incorporates two sets of accelerometers measuring acceleration in each of the three axes. The two 3D accelerometers are fixed to a frame so that their axes are aligned and they are separated by a prescribed distance. By calculating the difference in acceleration between the two 3D sensors, the gravitational component and linear acceleration components are cancelled leaving the rotational acceleration components. An onboard microcontroller digitises the accelerometer signals and the data is transmitted wirelessly to a PC to calculate the angular velocity with minimal latency. Tests were conducted on several subjects running at a constant velocity for several different speeds. The angular rate output from the accelerometer-based system was compared to data obtained from an optical motion analysis system. Validation test results indicate an accurate result was obtained. The design's suitability for acquiring data during elite athlete sprint training is examined and other applications considered. Error reduction strategies will also be discussed.