## 2 Materials and Methods
### Procedures  
Participants presented to the Biomechanics Laboratory at the University of Central Lancashire. In runners who experienced bilateral PFP, the limb that exhibited the greater symptoms was included [4]; for the control participants, the dominant limb (defined as the limb that would be used to kick a football) was utilized [20]. Participants in the PFP group completed the Knee Osteoarthritis Outcome Score Patellofemoral subscale (KOOS-PF); this scale is scored from 0 to 100, with 100 representing no disability and 0 representing maximum disability [30].  
Participants ran across the Biomechanics Laboratory, striking an embedded piezoelectric force platform (Kistler Instruments Ltd., Winterthur, Switzerland)--which sampled at 1000 Hz--with their appropriate foot. Participants were required to run in their usual running shoes and at their own typical/self-selected running speed. The stance phase was delineated as the duration over which 20 N or greater of vertical ground reaction force (GRF) was applied to the force platform [31]. Runners completed five successful trials, with a successful trial being defined as one where the foot made full contact with the force platform, and with no evidence of gait modifications due to the experimental conditions. Kinematic and GRF data were synchronously collected. Kinematic data were captured at 250 Hz via an eight-camera motion analysis system (Qualisys Medical AB, Gothenburg,Sweden). Dynamic calibration of the motion capture system was performed before each data collection session.  
Body segments were modelled in 6 degrees of freedom using the calibrated anatomical systems technique [32]. To define the anatomical frames of the thorax, pelvis, thighs, shanks, and feet, retroreflective markers were placed at the 7 th cervical vertebrae (C7), 12 th thoracic vertebrae (T12), and xiphoid process landmarks, and also positioned bilaterally onto the acrom process, iliac crest, anterior superior iliac spine (ASIS), posterior super iliac spine (PSIS), medial and lateral malleoli, medial and lateral femoral epicondyles, greater trochanter, calcaneus, and 1 st and 5 th metataralsals (Figure 1a). Intra-rater reliability for the researcher responsible for positioning of the aforementioned anatomical markers has been shown to be excellent [33]. The centres of the ankle and knee joints were delineated as the midpoints between the malleoli and the femoral epicondyle markers [34; 35]. The hip joint centre was determined using a regression equation that uses the positions of the ASIS markers [36]. Carbon-fibre tracking clusters comprising four non-linear retroreflective markers were positioned onto the thigh and shank segments. In addition, the foot segments were tracked via the calcaneus, first metataralsal, and fifth metataralsal, the pelvic segment was tracked using the PSIS and ASIS markers, and the thorax segment was tracked using the T12, C7, and xiphoid markers. Static calibration trials were carried out, allowing for the anatomical markers to be referenced in relation to the tracking markers/clusters. The \(Z\) (transverse) axis was oriented vertically from the distal segment end to the proximal segment end. The Y (coronal) axis was oriented in the segment from posterior to anterior. Finally, the X (sagittal) axis orientation was determined using the right-hand rule, and was oriented from medial to lateral (Figure 1b).  
Figure 1: (**a**) Experimental marker locations and (**b**) trunk, pelvis, thigh, shank, and foot segments, with segment co-ordinate system axes (R = right and L = left), (TR = trunk, P = pelvis, T = thigh, S = shank, and F = foot), (X = sagittal, Y = coronal, and Z = transverse planes).