Left step One step 60 Toe-oﬀ Right step 40% Swing 80 100 Initial contact 0 Initial contact 60% Stance 20 40 Figure 2: The gait cycle can be divided into the stance phase (weight-bearing) and swing phase (non-weight-bearing). Reprinted with permission: Elsevier Books (2857691435547). 2.4. Data Analysis. Data was exported from the Vicon software to Matlab (The Mathworks, Natick, MA, R13) for processing. Temporal-spatial variables were computed for each participant’s left and right leg gait cycles. A gait cycle is deﬁned as the time between consecutive foot strikes of the same limb. Each gait cycle is comprised of two steps and one stride (Figure 1). The gait cycle can be subdivided into the stance phase and swing phase. The stance phase refers to the weight-bearing portion of the gait cycle for a single limb and typically occurs for the ﬁrst 60% on average (Figure 2). The swing phase refers to the non-weight-bearing portion of the gait cycle for a single limb and typically occurs for the last 40% of the gait cycle (Figure 2). For each left and right limb gait cycle, the following temporal-spatial variables were computed: (1) cadence (steps/min): number of steps taken per minute (cadence = 120/cycle time, where cycle time is the duration of the gait cycle), (2) stride length (m): absolute horizontal distance trav- eled by the heel marker between two consecutive foot strikes of the same limb (Figure 1), Autism Research and Treatment Figure 1: One gait cycle, or stride, is deﬁned as two consecutive heel strikes of the same limb. Each gait cycle is composed of two steps. Reprinted with permission: Elsevier Books (2857691435547). 3 100 Initial contact Initial double support 10% 0 Initial contact 60% Stance 20 40 Terminal double support 10% 60 Toe-oﬀ 40% Swing 80 Figure 3: The gait cycle has two periods of double support, where both feet are weight-bearing. Reprinted with permission: Elsevier Books (2857691435547). (3) swing time (s): duration of time that the limb is not in contact with the ﬂoor (Figure 2), (4) stance time (s): duration of time that the limb is in contact with the ﬂoor (Figure 2), (5) double stance time (s): duration of time that both feet are in contact with the ﬂoor (Figure 3), (6) swing/stance ratio: ratio of swing and stance time. To identify the most suitable trial for analysis, cadence, velocity, and percent of cycle spent in single stance (i.e., single limb support) were computed for the left and right leg of each participant. The single left and right gait cycle that most closely approximated the respective mean of all gait cycles on these three measures was selected for ﬁnal analysis for each participant. For each temporal-spatial measure (TS), six measures of symmetry were computed: TSleft)]|. (1) symmetry ratio, ratio = TSright/TSleft, (2) symmetry index average, SIavg = [(TSright − TSleft)/ 0.5(TSright + TSleft)] × 100%, (3) symmetry index left, SIleft = [(TSright − TSleft)/ TSleft] × 100%, (4) symmetry index right, SIright = [(TSright − TSleft)/ TSright] × 100%, (5) symmetry angle [15], SA = [(45◦ − atan(TSright/ TSleft)) × 100%]/90, (6) gait asymmetry [16], GA = |100 × [ln(TSright/ 2.5. Statistical Analysis. Six symmetry indices were com- puted using 6 diﬀerent temporal spatial measures, for a total of 36 symmetry measures. Signiﬁcant (P < 0.05) diﬀerences in the six mean temporal-spatial parameters (Table 2) between the control and autism groups were tested using a MANOVA. Signiﬁcant (P < 0.05) diﬀerences in the mean symmetry indices (Table 3) between the control and autism groups were also tested using a MANOVA. All statistical tests were performed using SPSS Software (v17.0, IBM, New York, USA).