## 2 Materials and Methods
### Procedures  
Anthropometric measures included the following: height and body mass, as well as measures needed for the Plug-in-Gait (PIG) model (leg length, pelvic width, ankle and knee width, shoulder offset, elbow width, wrist width, and hand thickness). Retroreflective markers were placed directly on the skin using hypoallergenic double-sided tape according to the PIG model, OFM, and Vicon upper limb models [10; 17; 26; 27; 28; 29; 30; 31]. The PIG model was modified by the placement of medial knee and ankle markers. Nine-millimeter (mm)-diameter markers were placed on the feet. Foot markers were placed with the participants in a standing position in their preferred foot position, i.e., neutral, planus, or cavus. Medial and lateral hindfoot and midfoot markers were placed to best represent that position. Fourteen-millimeter markers were used at the other anatomical locations. To control for inter-rater variability within a study and between studies over three years, one trained researcher placed all markers. To ensure the fidelity of consistent and accurate marker placement three procedures were followed: (1) only one researcher for any given study year placed all markers; (2) marker placement was immediately checked by the senior researcher; (3) prior to experimental data collection, pilot gait data were collected and kinematic data were reduced and graphed relative to the laboratory control data set. Novice researchers were required to demonstrate lower extremity joint angle graphics to be within one standard deviation of the laboratory control data set (created by the lab director).  
Prior to squat data collection, a static subject calibration trial was performed and processed to create a unique subject skeletal model. The subjects were instructed to stand in the middle of the calibrated volume in an anatomical position with feet shoulder-width apart, knees slightly bent, and arms slightly abducted for four seconds. In addition, one walking trial was collected and processed, and kinematic data were graphed to assess the accuracy of marker placement on lateral and medial femoral condyles and thigh and tibial segments [32]. If hip internal/external rotation or knee varus/valgus joint angles exceeded the pre-determined normal band of one standard deviation outside the control mean, lateral thigh, medial femoral condyle, and lateral tibial marker placements were corrected, and the static subject calibration was repeated. A second gait trial would be checked for corrected hip and knee joint angles.  
After the accuracy of markers and related hip and knee kinematics were verified, OHDS data were captured. Participants were instructed by an examiner to complete the OHDS according to standard FMS(tm) instructions. These instructions were standardized to the FMS(tm) protocol for generalizability and applicability to assessment tools used in clinical settings. The motion capture procedure occurred as follows.  
Motion capture was initiated when the subjects were standing behind the force plates with hands down holding a dowel. Participants stepped forward onto the force plates with one foot placed in the center of each force plate, feet shoulder-width apart, to pointing generally forward (a standard foot position for all participants was not dictated) as comfortable for the subject without allowing greater than 15\({}^{\circ}\) talocrural rotation. The squat was performed to the subject's self-selected maximum depth with the dowel above their heads before returning to the starting position and stepping back off the force plates (Figure 1). Participants repeated the OHDS three times stepping off the force plate and stopping motion capture between each trial. If directions were not followed correctly, an additional trial was performed.