GAIT DEFICIENCIES IN INDIVIDUALS WITH DOWN SYNDROME: A MOTOR CONTROL PERSPECTIVE WITH IMPLICATIONS FOR PEDAGOGICAL INTERVENTION

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1 International Journal of Arts & Sciences, CD-ROM. ISSN: :: 6(3):57 65 (2013) GAIT DEFICIENCIES IN INDIVIDUALS WITH DOWN SYNDROME: A MOTOR CONTROL PERSPECTIVE WITH IMPLICATIONS FOR PEDAGOGICAL INTERVENTION Michael Horvat University of Georgia Ronald Croce University of New Hampshire Manuela-Cristina Barna University of Georgia To examine differences in control of gait between adults with Down syndrome (n = 12) and adults without disabilities (n = 12) two investigations were undertaken evaluating spatial and temporal gait parameters under varying and more complex task conditions. In the first experiment we compared gait parameters during a preferred walking speed and a fast walking speed. In the second experiment, we investigated participants abilities to adjust spatial and temporal gait parameters under conditions that required increased information processing, via a dual-task paradigm. We hypothesized these investigations would demonstrate that increased task complexity and increased competition for information processing would impede ambulatory performances in adults with Down syndrome. Based on data analyses, significant group differences were found across both spatial and temporal gait parameters (adults with Down syndrome had significantly poorer gait performances than adults without disabilities) in both experiments (p < 0.05). Moreover, in the first experiment adults with Down syndrome displayed more erratic and skewed gait performances during fast walking. In the second experiment there was a significant decrease in gait performance as competition for information processing increased, which was found more in adults with Down syndrome. Results indicated that although adults with Down syndrome displayed a typical walking pattern, it tended to be less efficient and less adaptable to changing environmental contexts than that found in their non-disabled peers. Furthermore, it appears that adults with Down syndrome lack the faculty to control gait patterns and that these inefficiencies most likely reflect a lack of early movement experiences, a lack of early-intervention, motor training programs, and/or deficiencies in utilizing sensory feedback. Potential pedagogical methodologies, such as using variable practice conditions and appropriate augmented feedback, are discussed as possible tools for remediation. Keywords: Dual-Task paradigm, Down syndrome, Motor control, Gait deficiencies. 57

2 58 Michael Horvat et al. Introduction Control of various spatial and temporal parameters is required to initiate, execute, and terminate movements (Horvat, et al., 2010). Synchronously, individuals respond to changes in the environment using sensory information to modify, or self-correct, their movements. This is evident when environmental conditions change, such as irregular terrain or needing to avoid obstacles, which require significant adaptations of movement. Consequently, efficient and controlled movement is dependent on the ability to adapt movement patterns and maintain stability throughout a sequence of controlled events while integrating sensory information to monitor performance (Horvat, et al., 2010). In adults with Down syndrome these control mechanisms are often askew, leading to atypical movement patterns. Because of motor control difficulties in these individuals, gait initiation, execution, and termination are often compromised. The inability to generate appropriate amounts of force, along with insufficient allocations of sensory information, may contribute to these problems (Rigoldi, et al., 2011). Although these problems do exist, when presented with appropriate education and motor training programs, adults with Down syndrome can improve their motor performances and often respond to training in similar -- albeit to a lesser extent -- way as their non-disabled peers (Croce & Rock, 1990). Based on a lack of empirically based studies comparing gait control strategies between individuals with and without Down syndrome, the following experiments were undertaken. These experiments compared gait patterns of young adults with and without Down syndrome on the GAITRITE electronic walkway under varying levels of task complexity. It was hypothesized that temporal and spatial information on common gait parameters would vary significantly as tasks changed and became more complex. Experiment 1 In the first experiment, Horvat et al. (2012a) compared spatial and temporal gait movement parameters on responses to a self-selected or preferred speed as if they were walking down a hallway (PREF). Participants were also instructed to walk at a fast walk as if they were in a hurry to get somewhere or if they were crossing the street (FW). Participants Twelve young adults with Down syndrome and 12 young adults without disabilities (18-28 years) were matched according to age and sex. Due to significant group differences in height and leg length, gait parameters were normalized for height and leg length according to the recommendations from the GAITRITE protocol (CIR Systems Inc. Clinton, NJ). Participants were recruited through local community agencies and public school. A medical professional performed diagnosis of Down syndrome with a mild intellectual disability. Methods The GAIRITE electronic walkway was used to assess spatial and temporal gait parameters at preferred and fast walking speeds. The GAIRITE electronic walkway is a mat (6.96 m of linear ambulatory space) with sensory pads (16,128 sensors arranged in a grid like pattern) that record

3 Gait Deficiencies in Individuals with Down Syndrome spatial and temporal components of gait. The system was designed to assess gait parameters and variations in function during specific protocols (CIR Systems Inc. Clifton, NJ). The validity of the system was established for individuals with Down syndrome in an earlier study (Gretz, et al. 1998). Gait parameters tested were based on an earlier protocol and were divided into spatial and temporal components (Wu, et al., 2007). Spatial components included stride length (distance between heel strikes of the same foot), step length, (distance between heel strikes of opposite feet), stride width (vertical distance from midpoint of one foot to the line formed by the midpoints of two footprints), step width (lateral distance between feet), base of support (perpendicular distance from heel point of one footfall to the line of progression of the opposite foot), and toe-in/toe-out (angle between line of progression and heel point to the forward part of the footfall). Normal toe-in and toe-out ratio was reported in degrees of deviation from the heel strike to the toe along the line of progression. Magnitudes were recorded as positive for toe-out and negative for toe-in while a score of zero was equated to parallel heel-to-toe movement along the line of progression. Temporal components included velocity (distance divided by ambulation time), single leg support time (time between last contact of current footfall to first contact of next footfall of the same foot), double leg support time (time between first contact of current footfall and first contact of next footfall), stance time (time between first and last contact of two consecutive footfalls on the same foot), step time (time from first contact of one foot to the first contact of opposite foot), and swing time (time between the last contact of the current footfall to the first contact on next step of the same foot). Participants were instructed to walk at the two chosen velocities, PREF and FW, and were allowed to practice each walk. Order of testing was counterbalanced over subjects through a sampling without replacement procedure. Results of three trials for each walk were averaged for the data analyses. Results Except for temporal variable velocity (which used a one-way ANOVA), statistical analyses included MANOVAs, descriptive summaries, and percent differences. Separate one-way ANOVAs were performed on the temporal variable velocity because this variable represented a total time to accomplish. Criterion for significance was set at p < Based on data analyses, there were: (1) significant group differences between adults with and without Down syndrome for step length, step width, stride length, and velocity under PREF condition; and, (2) significant task differences between PREF and FW for step length, step width, and stride length. Percentage differences also indicated that adults with Down syndrome had low mean scores for all spatial and temporal variables in relation to adults without disabilities (see Experiment 1, Tables 1 & 2). Overall data indicated that adults with Down syndrome were deficient in spatial and temporal components of gait. It was concluded that the ability of adults with Down syndrome to control gait movements was reflective of a lack of earlier movement experiences, a lack of earlyintervention, motor training programs, and/or deficiencies in utilizing sensory feedback (Horvat, et al., 2010).

4 60 Michael Horvat et al. Experiment 2 In experiment 1 we demonstrated that variations in spatial and temporal gait parameters existed between young adults with Down syndrome and age-matched adults without disabilities (Horvat,

5 Gait Deficiencies in Individuals with Down Syndrome et al., 2012a). This preliminary investigation provided the basis for our premise that individuals with Down syndrome have impaired motor control processes relative to gait and that the overall motor program for gait was not as robust as that found in individuals without disabilities. The consequence of this lack of robustness was reflected in their difficulties performing a faster than normal gait explicit to particular temporal and spatial components. This earlier work provided the rationale to investigate their abilities to adjust spatial and temporal gait parameters under conditions that required increased information processing from competing stimuli. Although the impact of increased information processing, via a dual task paradigm, on basic motor skill execution has been investigated extensively in the non-disabled population (e.g., Ebersbach, et al., 1995), as well as in other populations with disabilities (e.g., Parkinson Disease [O Shea et al., 2002]), it has not been thoroughly addressed in individuals with intellectual disabilities and Down syndrome. We theorized that our investigation would demonstrate that increased competition for information processing would impede ambulatory performances in this population. In the second experiment, Horvat, et al. (2012b) compared spatial and temporal gait movement parameters on responses to five tasks, each involving greater information processing and attention. Participants Twelve young adults with Down syndrome and 12 adults without disabilities (18-28 years) were matched according to age and sex. Due to significant group differences in height and leg length, gait parameters were normalized for height and leg length according to the recommendations from the GAITRITE protocol (CIR Systems Inc. Clinton, NJ). Process for participant recruited and professional diagnosis of Down syndrome with a mild intellectual disability were similar to that of experiment 1. Methods Similar to experiment 1, the GAIRITE electronic walkway was used to assess spatial and temporal gait parameters across conditions (tasks) tested. Gait parameters tested were based on an earlier protocol by Wu, et al. (2007) and were divided into spatial and temporal components. Spatial components included: stride length, step length, step width (lateral distance between feet), and stride width. Temporal components included: velocity, single leg support time, double leg support time, and step time (see experiment 1). The control condition (task) against which dual tasks were compared was walking at a selfselected, or preferred, speed (PREF). Dual tasks, in descending complexity, were buttoning a shirt (BS), talking on a cell phone (PH), carrying a tray with five cups (TC), and carrying a plate in one hand and a cup in the other hand (PC). A panel of three experts determined complexity levels of dual tasks. Participants had the shirt on prior to initiating the walk. Shirts each had seven buttons with men s buttons on the left side of the shirt and women s buttons on the right side of the shirt. Tray and cups consisted of carrying a 21 X14 serving tray with five empty plastic 8 oz. drinking cups with no lids spread over the tray. Carrying a plate and cup consisted of a 7 plastic dessert plate in one hand and an empty plastic mug, which holds four cups of liquid with handle and lid in the other hand. During the cell phone task the participant answered the phone and began conversing with the investigator prior to initiating the walking pattern. A script of predetermined questions was used for each participant during the walking task.

6 62 Michael Horvat et al. Results Temporal and spatial values were compared separately using a 2 (group [Down syndrome, without disabilities) x 5 (conditions [PREF, PC, TC, PH, SH]) repeated measures ANOVA for each of the variables analyzed. Criterion for significance was set at p < Based on data analyses, there were significant group differences (adults with Down syndrome had inferior performance) for all spatial variables and decreased gait performance as task complexity increased (i.e., increasing levels of information processing required). For temporal variables, group differences were found only for velocity and single-leg support, but not for step time and double-leg support; however, subjects in both groups showed decreased gait performance as task complexity increased (see Experiment 2, Tables 1 & 2). Discussion Results from these experiments indicated significant differences in various temporal and spatial gait parameters in adults with Down syndrome when compared to that found in adults without

7 Gait Deficiencies in Individuals with Down Syndrome disabilities. Overall, data indicated that although adults with Down syndrome displayed a typical walking pattern, it tended to be less efficient and less adaptable to changing environmental contexts than that found in their non-disabled peers. This was found in particular during tasks requiring greater levels of information processing (experiment 2), and indicated potential deficiencies in developing what Schmidt and others would phrase as an inadequate generalized motor program (GMP) for gait (Schmidt & Lee, 2011). According to Schmidt and Lee (2011), a motor program is an abstract representation of movement that centrally organizes and controls the many degrees of freedom (the number of independent parameters that are involved in performing an action). Signals transmitted through motor and sensory pathways allow the central nervous system (CNS) to anticipate, plan, and guide movements. The more engrained the motor program is within the CNS, the more flexibility and automicity one sees when movement is performed under varying environmental conditions and contexts. The GMP concept gives a solution to both storage and novelty problems of storing an immense number of individual motor memories (engrams) for all possible movements an individual performs. By modifying various movement parameters, such as force and timing of the movement, one could have a single motor program that could be customized for similar patterns or situations. In gait, for example, one could walk slowly or fast, trot, gallop, or run slowly or fast. The timing parameter during a preferred walk is slower than during a fast walk, yet the overall stepping pattern (e.g., stride length and width) is similar. In experiment 1 when the task required movements to be modified by increasing the pace, more variations in gait appeared in adults with Down syndrome (in FW condition large differences between groups were found in velocity, step length, step width, toe in/toe out, etc.), indicating adjustments to a different walking cadence from what is usually preferred (PREF condition) lead to gait inconsistencies. Latash (2000) and Smith, et al. (2010, 2011) also reported similar inconsistencies in this population and postulated that they were either less willing or unable to adjust their movements and apply an adaptive strategy to accommodate variability during movement. Problems in controlling gait became even more pervasive in experiment 2 where participants had to walk while performing additional tasks requiring increasing levels of information processing. This further indicated that in this population the GMP for gait was either less automated or was not practiced under sufficient environmental contexts. Another possible explanation for these deficiencies could be that adults with Down syndrome have a limited capacity in developing a strong GMP for ambulation and instead develop singular ambulation motor programs that make them less adaptable under varying ambulatory constraints or situations (Smith, et al., 2011). Given these gait inefficiencies, it is suggested that educational and training interventions should be structured so as to maximize automicity of the movement pattern and facilitate adaptation to changing environments and conditions. But what are the most efficacious methods to maximize gait acquisition and adaptation in this population? Feedback, along with practice, is considered to be one of the most potent variables affecting motor skill acquisition (Schmidt & Lee, 2011). When one performs a task, two types of performance-related information are available to the learner. The first type is intrinsic feedback. During motor performance, individuals are able to acquire substantial information about their motor performance through numerous sensory channels that are sensitive to movement. The second type is extrinsic feedback often referred to as augmented feedback. One of the most important categories of extrinsic or augmented feedback is knowledge of results (KR). This type of feedback refers to adding to or enhancing task-intrinsic feedback with an

8 64 Michael Horvat et al. external source. The external source may be a therapist, a teacher or a device such as a biofeedback system. Essentially, KR is verbal, terminal (sometime post-response) feedback regarding movement proficiency. Based on results from a multitude of empirical research, as feedback frequency decreases, performance is poorer during skill acquisition but, contrastingly, skill retention and transfer increases. This differential effect of KR frequency on acquisition performance versus retention and transfer has been espoused as the guidance hypothesis of KR and suggests that too much KR tends to subjugate internal information processing activities, thereby blocking intrinsic sources of information feedback important for error detection and analysis (Croce, et al., 1996). Another key teaching methodology to increase skill acquisition is varied practice (Schmidt & Lee, 2011). Varied practice (also known as variable practice or mixed practice) refers to the use of training schedules that include frequent changes of tasks so that the performer is constantly confronting novel representations of the to-be-learned information. Varied practice focuses on distributing practice in time, organizing activities to be practiced (blocked vs. random), and interspersing information or content to highlight distinctions that facilitate learning. For example, a varied practice approach to learning an appropriate gait might involve a sequence of ten slow walks, followed by ten fast walks, followed by ten intermediate speed walks, with the entire cycle repeating ten times. This could be further augmented by having the individual walk under differing contexts (e.g., different surfaces such as grass, tile, and carpet). This contrasts with traditional approaches in which the learner is encouraged to focus on mastering a particular aspect or subset of the relevant information before moving on to new problems (e.g., focusing on slow walking before attempting fast walking). With varied practice, the learner is exposed to multiple versions of the problem even early in training. In research with individuals with intellectual disabilities, variable practice conditions (e.g., Edwards, et al., 1986) and appropriate applications of augmented feedback (e.g., Croce & Rock, 1990) have been shown to facilitate learning, increase retention, maximize skill transfer, and make the learned skill more flexible and adaptable to situations outside the individual s comfort zone. Hence, incorporating sound teaching methodologies can enhance postural and gait control mechanisms in this population. References 1. Croce, R., Horvat, M., & Roswal, G. (1996). Augmented feedback for enhanced skill acquisition in individuals with traumatic brain injury. Perceptual and Motor Skills, 82, Croce, R., Horvat, M., & Roswal, G. (1995). Coincident timing by non-disabled, mentally retarded and traumatic brain-injured individuals under varying target exposure conditions. Perceptual and Motor Skills, 80, Croce, R., & Rock, S. (1990). The effects of four modes of reinforcement on fine-motor skill acquisition of mentally retarded adults. In R. French and B. Lavay (Eds.) Behavior management techniques for physical educators and recreators (pp ). Kearn, Nebraska: Educational Systems Associates. 4. Ebersbach, G., Dimitrijevic, M., & Powe, W. (1995). Influence of concurrent tasks on gait: A dual-task approach. Perceptual and Motor Skills, 81, Edwards, J., Elliott, D., & Lee, T. (1986). Contextual interference effects during skill acquisition and transfer in Down s syndrome adolescents. Adapted Physical Activity Quarterly, 3, Gretz, H.R., Doering, L.L., Quinn, J., Raftopoulos, M. Nelson, A.J., Zwick, D.E. (1998) Functional ambulation performance testing of adults with Down syndrome. Neurorehabilitation, 11,

9 Gait Deficiencies in Individuals with Down Syndrome Horvat, M., & Croce, R. (1991) Physical rehabilitation of individuals with intellectual disabilities, physical fitness and information processing. Critical Review of Physical Rehabilitation Medicine, 7; Horvat, M., Croce, R., Zagrodnik, J., Brooks, B., & Carter, K. (2012a). Spatial and temporal variability of movement parameters in individuals with Down syndrome. Perceptual and Motor Skills, 114, Horvat, M., Croce, R., Zagrodnik, J., Brooks, B., & Carter, K. (2012b). Dual tasking and gait variability in individuals with Down syndrome. Unpublished manuscript, University of New Hampshire. 10. Horvat, M., Croce, R., & Zagrodnik, J. (2010). Utilization of Sensory Information in Intellectual Disabilities. Journal of Developmental and Physical Disabilities, 22, Latash, M.L. (2000). Motor coordination in Down syndrome: The role of adaptive changes. In Weeks, D.J., Chu, R., Elliot, D. (Eds). Perceptual motor behavior in Down syndrome (pp ). Champaign IL: Human Kinetics. 12. O Shea, S., Morris, M., & Iansek, R. (2002). Dual task interference during gait in people with Parkinson disease: Effects of motor versus cognitive secondary tasks. Physical Therapy, 82, Rigoldi, C., Galli, M., & Albertini, G. (2011). Gait development during lifespan in subjects with Down syndrome. Research in Developmental Disabilities, 32(11), Schmidt, R.A. & Lee, T.D (2011). Motor control and learning: A behavioral emphasis (5 th edition). Champaign, IL: Human Kinetics. 15. Smith, B.A., Stergiou, N. & Ulrich, B. (2011). Patterns of gait variability across the lifespan in persons with and without Down syndrome. Journal of Neurological Physical Therapy, 35(4), Smith, B.A., Ashton-Miller, J.A., &Ulrich, B.D. (2010). Gait adaptations in response to perturbations in adults with Down syndrome. Gait and Posture, 32 (2), Wu, J., Looper, J., Ulrich, B.D., Ulrich D.A., & Angulo-Barrso, R.M. (2007). Exploring Effects of Different Treadmill Interventions on Walking Onset and Gait Patterns in Infants with Down syndrome. Developmental Medicine and Child Neurology, 49,