Abstract

BOTHA, J.; DOBSON, R.T.  and  DRIVER-JOWITT, J.P.. Development of a Device to Measure Human Response to Dorsiflexural Perturbation. R&D j. (Matieland, Online) [online]. 2007, vol.23, pp.28-34. ISSN 2309-8988.

The ability to balance is of fundamental importance to the safety of human beings. Damage to the brain and spinal cord through illness, injury or old age can result in balance problems, leading to the tendency to fall A device named the dorsiflexometer has been designed for the purpose of recording and analysing a patient's response to a perturbation leading to dorsiflexion, in order to aid in the diagnosis of balance impairment, particularly impairment caused by the conditions already described. The device consists of two tilting force platforms which measure the position and magnitude of the component of the resultant force normal to the platforms before, during and after dorsiflexural perturbation. The dorsiflexometer was constructed, calibrated and a number of balance tests were conducted using young healthy adults between the ages of 20 and 25. Three parameters which may be of use in diagnosis of balance impairments were identified: the radius of a circle enclosing all the recorded positions of the normal component of the resultant force applied to each force platform, a sway index, defined in the article, and the Lyapunov exponent, which is an indicator of whether or not a process is chaotic in nature, as calculated for the movement of the point of application of the resultant force. A computer program was written to analyse the raw data and plot the change in position of the normal component of the resultant force applied to the force platform. The Lyapunov exponents indicated that a human's postural control processes are chaotic in nature. This implies that standard statistical methods may not be an appropriate tool to analyse such results.

Keywords : Force platform; radius parameter; sway index; Lyapunov exponent; postural control; balancing ability.