Table 1: Participant characteristics for the autism group. Age (years) Height (cm) Weight (kg) 5.25 5.50 5.83 8.42 5.33 5.33 5.67 5.75 8.25 5.91 5.67 9.08 118.5 113.0 116.0 136.5 113.0 124.0 113.0 108.5 135.0 115.5 99.1 160.2 23.1 26.5 25.4 45.4 20.2 30.6 22.7 21.3 51.9 22.0 14.5 48.1 Autism Research and Treatment Diagnoses No known diagnoses No known diagnoses Generalized mild hypotonia Gross motor delay No known diagnoses Generalized mild hypotonia Generalized mild hypotonia Gross motor delay Joint hypermobility No known diagnoses Mild central hypotonia Gross motor delay No known diagnoses No known diagnoses 2 Subject Male Female Male Male Male Male Male Male Male Male Female Male study (mean age = 5.9 yrs; mean height = 120.06 cm; mean weight = 28.67 kg). All of the children had been previously diagnosed with autism spectrum disorder; however, none of the children were diagnosed with Asperger’s or otherwise nonspeciﬁed disorder. Further participant characteristics are provided in Table 1. Previously published control data [7] was used for data comparisons and consisted of twenty-two (n = 22) children aged 5–9 years (mean age = 6.22 yrs; mean height = 119.42 cm; mean weight = 28.66 kg). The control group was matched to the autism group based on age, weight, and height. Children were not matched based on IQ as it is not necessarily an appropriate criterion for matching on experiments involving motor tasks or children with devel- opmental delay. Ethical approval for this study was obtained from the University of New Brunswick Research Ethics Board. Parental consent and child assent were obtained prior to each child’s participation in the study. 2.2. Instrumentation. An eight camera Vicon MCam motion capture system (Oxford Metrics Group Ltd., Oxford, UK) tracked the three-dimensional trajectories of reﬂective mark- ers (25 mm diameter) placed on the participants’ heel during barefoot walking. Marker trajectories were sampled at a frequency of 60 Hz. Four force plates (Kistler Instruments, Winterthur, Switzerland) were used to measure the three- dimensional forces and moments during gait at a sampling frequency of 600 Hz. The force plates consist of four triaxial transducers at each corner that measure load. The plates were embedded in the laboratory ﬂoor and disguised with ﬂooring to prevent targeting by the subjects. Force plates provide information on the interaction of the foot with the ﬂoor. As the foot contacts the plate, reaction forces are generated in an equal and opposite direction to the applied load. The examination of these ground reaction forces facilitates the identiﬁcation of foot contact and lack of contact with the ground. The timing of these force events can then be used to estimate temporal-spatial parameters of gait. This work was part of a larger study that examined diﬀerences in kinematic and kinetic gait parameters in children with autism versus a control group [7]. As a result, the combined use of camera-based systems and force plates was required versus other methods of obtaining temporal- spatial measures. 2.3. Procedures. Data collection occurred at the motion anal- ysis laboratory at the University of New Brunswick (UNB). A reﬂective marker was placed directly on the posterior aspect of the right and left calcaneus at the Achilles tendon attach- ment [19]. Several “warm-up” trials were conducted to allow the participants to adjust to the markers and the laboratory environment. Children were then encouraged to perform as many gait trials as possible. For reliability, at least 7 trials were recorded for each leg. Trials consisted of walking a distance of 25 ft along an unmarked walkway. The physiotherapist positioned each participant at the start line while the parent of the participant waited at the end of the walkway. The start line was located 12.5 ft from the center of the plates allowing each participant to achieve steady state velocity by the time they reached the plate area (recording area). To promote successful force plate strikes with the foot (i.e., one entire foot on a single plate only), the physiotherapist adjusted the starting position of each participant. Verbal instructions to each participant included “look at your mom/dad” (to prevent the child from noticing and potentially targeting the force plate area) and “just walk” (to prevent running). Each trial was approximately 8 seconds in duration (time required to walk 25 ft), and the test session lasted approximately 45–60 minutes. It was anticipated that the experimental procedures could be challenging for the autism group due to skin sensi- tivities and an unfamiliar laboratory environment. However, the presence of family members and a physiotherapist with extensive experience with children with autism at each data collection session facilitated successful gait measurements and adherence to verbal requests.