Teach-in '99 : Toe Clearance
by Chris Kirtley, The Hong Kong Polytechnic University

During swing phase, the foot is lifted then swings through, making an arc centred at the knee. One important consequence of this is that during mid-swing the height of the foot is at a minimum, as shown in this animation (made using Vicon BodyBuilder modelling software). The height of the right toe from the floor is less than 20 mm at its minimum. In fact, David Winter has reported it as being, on average, 13 mm for young adults and only 11 mm for the elderly*.

At this point in the gait cycle, the toe is at great risk of striking a small obstacle, which may cause a stumble and fall. Reduced clearance may be therefore one important cause of falls in older people, which are associated with a large number of fractured femurs and other serious morbidity. Considering the potentially disastrous consequences of a fall, one wonders why the body has evolved such a dangerously small clearance. This is especially surprising when one considers that in stone-age times, the terrain over which our ancestors walked must have been very rough, with many obstacles to trip over.

*Winter, DA (1991) The biomechanics & motor control of human gait: normal, elderly & pathological (2nd. ed.), Univ. of Waterloo Press,
Waterloo, Ont.., p. 9.


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