Energetic optimization during over-ground walking in people with and without Down syndrome.

Individuals with Down syndrome (DS) show reduced gait stability that may increase the metabolic rate (MR) during over-ground walking and alter their energetic cost per unit distance (EC(transport)) to speed relationship. If so, the preferred walking speed (PWS) of people with DS may coincide with their speed at minimal EC(transport), reflecting energetic optimization. This study therefore examined whether MR and EC(transport) during over-ground walking differ between individuals with and without DS and whether PWS minimizes their EC(transport). Expired gases were collected from 18 individuals with DS and 18 without during six over-ground walking trials, each lasting 6 min, at PWS and at 0.51, 0.76, 1.01, 1.26, and 1.51 m/s. Gross- and net-MR, and gross- and net-EC(transport) were expressed in dimensionless form. Energetically optimal walking speeds and minimal gross- and net-EC(transport) were determined from the gross- and net-EC(transport) to speed curves for each participant. Individuals with DS showed higher gross-MR, net-MR, gross-EC(transport), and net-EC(transport). PWS minimized gross-EC(transport) in participants with DS, but not in those without. PWS did not minimize net-EC(transport) in either group. Therefore, gross-EC(transport) minimization during over-ground walking may determine PWS when impairments alter the gross-EC(transport) to speed relationship.