## 2 Materials and Methods
### Procedures  
Initial screening of potential participants was conducted over the phone to determine their eligibility for participation based on the inclusion and exclusion criteria (Table 1). Potential participants that passed the initial screening attended an in-person screening appointment in alignment with their \"on\" medication times. The MoCA and Berg Balance Scale were administered as screening measures for significant balance impairment, fall risk, and notable cognitive impairment. Once consent was obtained from qualified participants, they then completed the FOG Questionnaire, and data regarding demographic information (Table 2), medical and PD history, fall history, and current medications were collected. A physical screen assessed postural alignment andgait, and anthropometric measurements were taken for knee and ankle widths, leg length, pelvic width, height, and depth for body modeling consistent with the Plug-In Gait (PIG) model ([[http://www.vicon.com](http://www.vicon.com)]([http://www.vicon.com](http://www.vicon.com)) (accessed on 17 April 2023)). Data collection for three-dimensional (3D) motion walking trials with turns was performed in a single session in a quiet biomechanical laboratory setting. Participants wore their preferred athletic-type walking shoes. Men wore tight-fitting shorts and no shirt, and women donned tight-fitting shorts and a sports bra. A single trained (approximately 3 months) examiner placed 40 double-sided tape markers on the body following the full body PIG model with the use of extra tape to secure marker bases to the skin and shoes to prevent markers from falling or being kicked off when turning. Foot markers were placed directly on the participants' shoes. The PIG model was modified by placing markers on the head of the fifth metatarsal. The PIG model marker location modifications also included thigh marker placement on the mid-lateral thigh and tibial markers on the mid-lateral shank. Wands were not used for thigh and tibial markers. See the Appendix A Table A1 for \begin{table}
\begin{tabular}{l l l} \hline \hline
**Methods** & **Reduction** & **PIG** \\ \hline PD Group & PD Group & 1. & Surgery or orthopedic injury within 6 months that may interfere with ambulation (LE joint replacements fractures, injuries) \\
2. & Able to ambulate \(\geq\)14 m without AD & 2. & Significant medical conditions (hypertension, unstable heart disease, uncontrolled DM) \\
3. & Vestibular dysfunction within 6 months (BPPV, vertigo, [PERSON]’s disease, bilateral vestibular loss) \\
4. & Berg Balance Scale (BBS) \(\leq\) 36 & 5. & Montreal Cognitive Assessment (MoCA) \textless{}21 Self-report of \(\geq\)2 \\  & & falls per month & 6. & Diagnosis of another neurological disorder besides PD \\
7. & Deep brain stimulation & 7. & Deep brain stimulation \\ \hline \hline \end{tabular}
\begin{tabular}{l l} \hline \hline CON Group & CON Group \\
1. & Same inclusion criteria as the first three items of the PD group \\  & PD group & 1. & Same exclusion criteria as the first five items of the PD group \\
2. & Same decade of life and gender as a participant in the & 2. & Diagnosis of a neurological disease such as PD, multiple sclerosis, seizure disorder, brain injury, or history of stroke \\  & PD group & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Inclusion and exclusion criteria for Parkinson’s disease and Control participants. references regarding the validity and reliability of the PIG model, a list of markers, marker abbreviations, and placement descriptions. Following marker placement, a static subject calibration trial was completed, which combined participant anthropometric and marker position data to create a unique skeletal model for each participant. Participants stood still in an anatomical position to capture marker positioning for 1-4 s. The ability of the cameras to see all markers was verified. The medial femoral condyle and medial malleolar markers were removed following the completion of the static calibration trial.