Unconscious Bias in Walking

Abstract

MR. LARDEN'S letter in your issue of the 17th inst. (p. 262) regarding “circling to the left in a mist,” and the replies of Messrs. G. H. Darwin and Hawksley, have opened an interesting question, and one which seems to be but imperfectly understood. The true explanation of this vexed question has for some years appeared to me to be that to which it is attributed by Mr. Hawksley, namely, inequality in the length of the legs. A few years ago I made some investigations on the length of the lower limbs in man, the results of which were published in the Journal of Anatomy and Physiology, vol. xiii. p. 502 (1879). I found that of seventy well-authenticated skeletons which I examined, the lower limbs were equal in length in only seven instances, or in 10 per cent.; in twenty-five instances, or 35.8 per cent., the right limb was longer than the left, while in thirty-eight instances, or 54.3 per cent., the left limb was longer than the right. The left leg I found not only to be more frequently longer than the right, but the difference in length between the two limbs is greater on an average when the left is the longer. Inequality in length is not confined to any particular age, sex, or race, but seems to be universal in all respects. My observations corroborated those of several American surgeons made on the living subject. The result of one limb being longer than the other will naturally be that a person will unconsciously take a longer step with the longer limb, and consequently will circle to the right or to the left according as the left or right leg is the longer, unless the tendency to deviation is corrected by the eye. The left leg being more frequently the longer, circling should, if this theory of its being due to inequality of the limbs be correct, take place more frequently to the right than to the left. This is precisely what we find to obtain, and in this respect Messrs. Larden, Darwin, and Hawksley's observations agree with some I made myself on this question. The diameter of the circle formed by those circling to the right should, if my observations on the skeletons be correct, be less than that made by those circling to the left, since the difference in length between the two limbs is greater when the left is the longer.