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 (ECtransport) to speed relationship. If so, the preferred walking speed (PWS) of people with DS may coincide with their speed at minimal ECtransport, reflecting energetic optimization. This study therefore examined whether MR and ECtransport during over-ground walking differ between individuals with and without DS and whether PWS minimizes their ECtransport. 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-ECtransport were expressed in dimensionless form. Energetically optimal walking speeds and minimal gross- and net-ECtransport were determined from the gross- and net-ECtransport to speed curves for each participant. Individuals with DS showed higher gross-MR, net-MR, gross-ECtransport, and net-ECtransport. PWS minimized gross-ECtransport in participants with DS, but not in those without. PWS did not minimize net-ECtransport in either group. Therefore, gross-ECtransport minimization during over-ground walking may determine PWS when impairments alter the gross-ECtransport to speed relationship.