Pathological gaits: inefficiency is not a rule.

Theenergy expenditure per unit distance, or cost of gait, depends on the efficiency of the locomotory mechanism, which is a function of speed. We compared the cost of gait at corresponding speeds between pathologic (hemiplegic, above-knee amputee, paraplegic) and normal subjects respectively, using a polynomial regression on data available from the literature. In all pathologies the cost-speed function showed a minimum at a speed which may be defined as optimum, as in normal gait. Within the speed range possible for the patients, the cost-speed functions were significantly different from the normal one in the above-knee amputee and in the paraplegic, but not in the hemiplegic. In the amputee, the minimum cost was increased by 38% with respect to that of the normal at a corresponding speed. In contrast, the minimum cost was increased by only 11 % in the paraplegic, despite the much more severe impairment.