Exp Brain Res (2008) 186:261–272 DOI 10.1007/s00221-007-1230-7 123 RESEARCH ARTICLE Strategy adoption and locomotor adjustment in obstacle clearance of newly walking toddlers with down syndrome after diVerent treadmill interventions Jianhua Wu · Dale A. Ulrich · Julia Looper · Chad W. Tiernan · Rosa M. Angulo-Barroso Received: 27 October 2006 / Accepted: 21 November 2007 / Published online: 7 December 2007  Springer-Verlag 2007 Abstract This study investigated how newly walking toddlers with Down syndrome (DS), after diVerent tread- mill interventions, adopted clearance strategies and modi- Wed anticipatory locomotor adjustment patterns to negotiate an obstacle in their travel path. Thirty infants with DS (about 10 months of age) were recruited and randomly assigned to either a lower-intensity, generalized (LG) tread- mill training group, or a higher-intensity, individualized (HI) treadmill training group. Thirteen in each group com- pleted a one-year-gait follow-up after the treadmill inter- vention. Initially, both groups chose to either crawl or walk over an obstacle. However, walking over the obstacle became their preferred clearance strategy over the course of the gait follow-up even though the height of the obstacle increased from visit to visit. The HI group used the strategy of walking over the obstacle at a considerably higher per- centage than the LG group within 6 months after the train- ing. When approaching the obstacle, both groups started to show consistent anticipatory locomotor adjustments about 6 months after the training. Both groups decreased velocity, cadence and step length, and increased step width at the last three pre-obstacle steps. It was concluded that the retention of the HI training eVects led the HI group to predominantly walk over an obstacle earlier than the LG group within 6 months after treadmill intervention, and the two groups produced similar anticipatory locomotor adjustments in the last three steps before negotiating the obstacle. Keywords Infant · Down syndrome · Early intervention · Obstacle · Adaptation Introduction Down syndrome (DS) is a genetic disease caused by an extra copy of human chromosome 21. The incidence of DS is about 13.65 out of 10,000 live births in the United States (CDC 2006). It is well established that people with DS have diVerent brain structure and function compared to their peers with typical development (TD). From autopsy studies (Becker et al. 1986; Scott et al. 1983; Wisniewski 1990), magnetic resonance imaging studies (Aylward et al. 1997; Kesslak et al. 1994; Pinter et al. 2001), and mouse models of DS (Baxter et al. 2000; Roper et al. 2006), DS has been related to decreased brain weight and size, disproportion- ately smaller cerebellar volumes, decreased cortical sulca- tion, a reduced number and density of neurons, and reduced synaptic formation. In addition to cognitive deWciencies more related to the central nervous system, children with DS also show sensorimotor impairments such as slower somatosensory conduction velocity (Brandt and Rosen 1995), and deWciencies of the visual system such as poorer performance of visual acuity and contrast sensitivity (Courage et al. 1997; Courage et al. 1994). Many of the aforementioned deWciencies in DS may cause signiWcant delays in the achievement of both gross and Wne motor skills in this population (Henderson 1986). For example, the achievement of independent walking is, on average, one year later in infants with DS compared to their peers with TD (Henderson 1986; Ulrich et al. 2001). J. Wu · D. A. Ulrich · J. Looper · C. W. Tiernan · R. M. Angulo-Barroso (&) Motor Development Laboratory, Center for Motor Behavior and Pediatric Disabilities, Division of Kinesiology, University of Michigan, 401 Washtenaw Avenue, Ann Arbor, MI 48109, USA e-mail: rangulo@umich.edu J. Wu e-mail: wjhwu@umich.edu