Introduction

A measurement system based on a triaxial accelerometer and a portable data logger has been developed and four performance parameters have resulted from experimental testing [3]. These are sensitive to balance-related changes introduced in the gait pattern. They are: correlation between the signals of all the possible pairs of steps in a walking sequence (aI), area under the power spectrum curve having first subtracted the regular part of the signal (aII), variation in stride duration (aIII), and conservation of mechanical energy (aIV) [4]. Parameter aI detects step signals that deviate from the normal morphology by being either too regular or too irregular; aII is related to the neuromuscular effort to maintain balance; aIII detects cadence irregularities and aIV detects inefficiencies in gait which are sometimes related to imbalance. Quantitative balance measurements can be useful in monitoring illness, or the effectiveness of therapy. They can also be a research tool in biomechanics, human factors or behaviour studies. The evaluation of balance can be made under different cognitive conditions, by introducing dual tasks to help discern between apparently normal and truly normal balance [1].

Methods

A triaxial accelerometer was placed on the subject’s back at the approximate height of the centre of mass. The sensor was attached to the body with a motorcyclist belt and levelled with respect to gravity. Data were recorded on a data logger worn around the neck. Nine normal subjects between 23 and 27 years of age volunteered. Besides walking with their usual gait, they were asked to walk with two balance challenging patterns: along a thin line -- reducing the base of support -- and walking with locked knees -- introducing a mechanical inefficiency and a greater difficulty to recover after a physical disturbance. All walks were also performed under dual task conditions for which the subjects were asked to subtract the number four, six or seven successively starting at 600 or 700. Twelve sets of data were gathered from each subject corresponding to two 35 m walking sequences under each of the six test conditions.

Results

Statistical tests showed the performance parameters can distinguish in a unique way between the different gait patterns tested. Statistical results pertaining to dual tasking are mostly not significant, as would be expected of normal individuals [2].

Discussion

Used together, the performance parameters can be useful in the evaluation of walking balance. The system is portable making long term measurements and measurements outside of the laboratory possible. Each subject acts as his or her own control. The instrumentation is inexpensive. The present test is easy to administer and easy to interpret.

References

1. Geurts, A.C.H.; Mulder, T.W.; Nienhuis, B.; Rijken, R.A.J. (1991). Dual-task assessment of reorganization of postural control in persons with lower limb amputation. Archives of Physical Medicine and Rehabilitation, 72, 1059-1064.
2. Sánchez-Pineda, A. (1997). Evaluación de la Estabilidad en Marcha para Aplicaciones Clínicas Mediante Acelerómetros en Sujetos Normales. Biomedical Engineering Degree Thesis, Universidad Iberoamericana, Mexico.
3. Waarsing, J.H. (1996). Quantifying the Stability of Gait using a Triaxial Accelerometer. Masters Thesis in Electrical Engineering, University of Twente, Enschede, The Netherlands.
4. Winter, D.A. (1979). A new definition of mechanical work done in human movement. Journal of Applied Physiology, 46, 79-83.