## 2 Materials and Methods
### Procedure and Data Collection  
All recruited PD patients underwent 3D motion analysis at Functional Anatomy Laboratory of University of Campania \"[PERSON]\" following a two-part procedure: the first part at T0, before the prolonged treatment with K1 Posture Keeper shirt, and the second at T1, after three months with the orthosis. Each part was further divided into two sessions: in the first, the patients were assessed without the K1 shirt, while in the second one, they were wearing the orthosis. Therefore, the entire procedure consisted of four conditions: T0 without K1, T0 with K1, T1 without K1, and T1 with K1. The healthy group was acquired only at T0 without the orthosis. Each measure was collected in a static condition, with subjects in upright standing position, and a dynamic one, walking barefoot on a 6 m walkway at a self-selected normal-pace speed. Walking trial was performed three times consecutively. Healthy group was acquired only during upright standing, collecting all parameters only in static condition. For each subject, the following preparation steps were applied before the acquisition:  
In the first session, an expert operator (physisatrist, expert in functional anatomy and 3D motion analysis) identified body landmarks, where the reflective markers were placed according to the DB-Total marker set protocol (Figure 2). Figure 2: (**a**) DB-total marker set on frontal plane anterior (**a\({}_{\rm II}\)**) and posterior (**a\({}_{\rm II}\)**) prospective. (**b**) PD patient wearing K1 Posture Keeper. Figure notes: cervical (C), thoracic (T), lumbar (L), sacrum (S), nasion (Ns), frontozygomatic suture (FZs), acromioclavicular joint (ACj), epicondylus humeri (eH), ulnar styloid (Us), anterior superior iliac spine (ASIS), greater trochanter (gT), medial (mEF) and lateral (IEF) epicondylus femoris, fibular head (Fh), medial (mM) and lateral (IM) malleoli, metatarsal heads (MtHs), and heel (He). In the second session, the same operator circled the T7, T12, L3, L5, and S2 markers using a demographic pen and removed them. Subsequently, he placed circular double-sided stickers inside the body landmarks (Figure 3a) and then, the cover of the stickers was removed (Figure 3b). Afterwards, the patient was instructed on how to wear the orthosis and the operator ensured that the shirt adhered to the patient's back, making the sticker signs visible (Figure 3c). Finally, the reflective markers were placed on the orthosis at the body landmarks, identified thanks to visible sticker signs (Figure 3d). At the end of the study, the Quebec User Evaluation of Satisfaction with Assistive Technology (QUEST) questionnaire [45] was administrated to the PD group to assess the benefit perceived in wearing the orthosis and their satisfaction (values range from 1 to 5). The following eleven whole-body parameters defined in previous studies [5; 6] were calculated on the sagittal plane by BTS Smart Clinic Software (1.10): sagittal vertical axes (SVAs), C7-nasion (CNA), cervical tilt (CT), dorsal (DA), lumbar (LA), trunk tilt (TT), heel-S2-nasion (HSN), heel-S2-C7 (HSC), heel-S2-T7 (HST), heel-S2, S2-C7 (SCA), and S2-T7 (STA) angles. Moreover, the occup point was obtained with a specific algorithm implemented by BTS software in order to calculate two other sagittal angles in PD and healthy groups, heel-S2-occipit (HSO) and S2-C7-occipit angles (SCO). All parameters were exported from BTS software and imported into MATLAB ([[https://www.mathworks.com/products/matlab.html](https://www.mathworks.com/products/matlab.html)]([https://www.mathworks.com/products/matlab.html](https://www.mathworks.com/products/matlab.html)), accessed on 15 February 2025) for further processing.