Graduation date: 2008It has been previously suggested that the walking pattern of individuals with Down syndrome is inefficient. This is thought to result from increased instability, particularly in the medio-lateral direction, due to the characteristic joint laxity and muscle hypotonia of individuals with DS. Therefore, this work was an attempt to gain insight into the efficiency of gait in adults with DS by studying their mechanical and metabolic characteristics during treadmill walking. The first study examined the three-dimensional motion of the center of mass (COM) and the spatio-temporal characteristics of adults with and without DS at a variety of walking speeds. Fifteen adults with DS and 15 adults without DS walked on a treadmill at six and seven randomly presented dimensionless speeds (Froude numbers), respectively, during which kinematic data were collected. The range of medio-lateral COM position was greater in participants with DS, but the ranges of vertical COM position and anterior-posterior COM velocity did not differ between the groups. Participants with DS walked with faster steps across all speeds. Their step length was shorter only during slow walking and their step width did not differ from adults without DS. Participants with DS were more variable in medio-lateral and vertical COM position, anterior-posterior COM velocity, and in all spatio-temporal parameters than their controls. The second study examined whether the net VO₂ and the net VO₂ per unit distance across the same walking speeds are different between adults with and without DS. The study also examined the relationship between the energetically optimal walking speed (EOWS) and the preferred walking speed (PWS) in both populations. Respiratory gases were collected from 14 adults with DS and 15 adults without DS as they walked at the same Froude numbers as for the first study. Adults with DS showed a higher net VO₂ and net VO₂ per unit distance, and a slower EOWS compared to adults without DS. The PWS was the same for both groups and did not appear to minimize the net VO₂ per unit distance in adults with DS. It was collectively concluded that the gait of adults with DS possesses several characteristics of inefficiency and has increased energetic requirements. Adults with DS do not prefer to walk at speeds that minimize the metabolic demand.