Autism Spectrum Disorder (ASD) is a complex neurodevelopmental disorder which has seen an increasing prevalence rate in recent decades. Currently, the diagnostic criteria for the disorder evaluate a multitude of social communication and interactions, in a variety of contexts, and restricted or repetitive behavioral patterns (stereotyped movement, resistance to changes in routines, restricted interests, and hyper- or hypo-reactivity to sensory stimulus). Furthermore, ASD severity is based upon the marked severity of the above described impairment and they must also fall within one of three potential categories:​ 1) symptoms being present in early development, although potentially not manifested fully;​ 2) the symptoms causing clinical impairment in areas of functional necessity (i.e. social, occupation);​ and/or 3) symptoms are not “better explained” by an intellectual disability. However, there is currently a large contingent of movement-related researchers examining the claims made by Leo Kanner when he initially termed walking patterns in children with ASD as “clumsy” and “uncoordinated” following a qualitative analysis. Aside from examining walking patterns in children, young adults, and adults with ASD, research has also focused on a variety of other movements such as reaching and grasping, postural control and balance, and even hopping which have mostly found that individuals with ASD exhibit differences in movements relative to peers with typical development (TD), regardless of the age examined. Furthermore, it has become increasingly popular among researchers that motor impairments may be a core feature of ASD.

Although there has recently been increased attention from motor-related science examinations in individuals with ASD, there currently is still a paucity of progressive evidence examining and quantifying motor impairments. Therefore, the purposes of this multiple-project dissertation were to:​ 1) examine hip, knee, and ankle joint position and vertical and anterior/posterior ground reaction force symmetry in children with ASD during over-ground walking;​ 2) quantify changes in lower extremity gait symmetry mechanics in children with ASD during over-ground walking while carrying a backpack (BP) filled with 15% of the participants’ body mass (BM) and while wearing a weight vest (WV) filled with 15% BM, evenly distributed over the trunk;​ and 3) to determine the effects of WV and BP carriage on lower extremity coordination in comparison to baseline, unloaded walking in children with ASD.

To answer the research question posed in the first purpose, ten children, aged 5-12 years, with clinical diagnoses of ASD, completed 20 walking trials at a self-selected pace while simultaneous three-dimensional kinematic (movement pattern) and kinetic (force parameters) data were collected. For this purpose, it was revealed that children with ASD exhibit asymmetrical lower extremity joint motion throughout the hip, knee, and ankle joints, when comparing the right and left joints, throughout the entire gait cycle. Additional asymmetries were found in anterior/posterior ground reaction forces (AP_GRF), while asymmetries existed in vertical ground reaction forces (vGRF), they were minimal in number. Most importantly, there was not a consistent pattern of where asymmetries occurred in the gait cycle throughout the participants, and all participants exhibited highly individualist asymmetries in and among the limbs and joints. With gait asymmetry being an indicator of gait health, the findings of the current purpose suggest that children with ASD exhibit gait patterns which may be classified as pathological, rather than healthy.

For purpose two, eight male children, aged 5-17 years, with clinical diagnoses of ASD completed 45 total walking trials in three experimental conditions:​ 1) walking over-ground without any added mass, BP, or WV;​ 2) walking over-ground while wearing a modified WV filled with 15% BM evenly distributed throughout the vest;​ and 3) walking over-ground while wearing a backpack loaded with 15% BM. Conditions 2 and 3 were completed in a counterbalanced order, ensuring baseline data was not influenced by Conditions 2 and/or 3. In purpose one, gait velocity was not measured or controlled for due to the heterogeneity previously observed, however, for purposes two and three, gait velocity was controlled for in post processing, utilizing trials which fell between ± one standard deviation of their baseline average gait velocity. It was found that asymmetries still existed in the lower extremity joints with both the WV and BP conditions, for each child, and when collapsed across the group, with similar numbers of asymmetries to baseline. However, participants displayed individualized kinematic symmetry responses to the different load conditions, relative to the baseline condition. For instance, some participants exhibited greater asymmetry in the WV condition, relative to baseline, whereas the BP condition invoked lesser asymmetry.

To further build upon the previous two projects, purpose three utilized a higher-order mathematical concept, continuous relative phase (CRP), to quantify lower extremity coordination in 10 children with ASD, aged 5-17 years, during unloaded and loaded over-ground walking. While it has been alluded to throughout the literature that individuals with ASD exhibit uncoordinated movement, there is a paucity of literature quantifying these claims. Fournier and colleagues completed a synthesis and meta-analysis on 51 papers all having examined motor coordination, in a sense. However, many of these studies qualitative measures were utilized to assess coordination whereas CRP is quantitative and objective method to compute coordination between segments, thus, removing any subjectivity from the analysis and providing quantitative empirical evidence for or against coordination impairments. Data were collected using identical methods as purpose two. When examining the group of children with ASD, it was found that children did not exhibit significantly different coordination patterns between the unloaded and loaded conditions. To determine if there was an accommodation influence, comparisons were made between the first and last 10 strides. From this, it was found that minimal differences occur between and among the various stride blocks.

Due to the individualistic nature of motor presentations of ASD, the third chapter also utilized single-subject analyses aiming to identify how individuals responded to the weighted conditions. When collapsing the individual statistical findings across the group, children with ASD exhibit differences in coordination patterns relative to unloaded walking. However, these differences are limited in terms of magnitude of meaning due to the limited number of large effect sizes (ES;​ ES >​ 1.2). Nevertheless, the findings from this purpose illustrate that children with ASD do exhibit different coordination patterns when walking with a BP or WV filled with 15% BM, although these differences are minor and may not have an influence on the outcome of ambulatory success. Further examination of the single-subject results illustrated that children with ASD exhibit more variable gait patterns in the unloaded condition compared to the two loaded conditions.

In summary, motor impairments in children with ASD are a vital component needing to be analyzed to obtain a more comprehensive understanding of the disorder. Through the first two purposes of this multiple-project dissertation, it has been illustrated that gait asymmetry is a pervasive metric which offers vital insight into motor characteristics within this population. Furthermore, the third purpose of this dissertation provided quantitative evidence that children with ASD, as a group, do not exhibit different coordination patterns, relative to baseline, during loaded walking. Conversely, when examined at an individual level, children with ASD do present with different coordination patterns during weighted walking. Furthermore, the findings of demonstrate that variable coordination patterns are diminished during weighed walking. Even with the findings of the current dissertation, further research is needed relative to coordination patterns during movement, and more so into utilizing treatments or interventions aimed at altering coordination in an effort to understand likely varied response patterns.