## 4 Discussion  
Using a retrospective case-control approach, this study evaluated running biomechanics in patients with and without PFP via a musculoskeletal simulation-based approach, and also investigated potential distinctions in PFP presentation between the sexes. This study represents the first exploration of the biomechanical parameters linked to the aetiology of PFP using musculoskeletal simulation, and may yield important clinical information for efforts towards the cessation of symptom initiation and the improvement of PFP management. Notably, patellofemoral stress indices were statistically greater in the PFP group compared to controls. This supports the notion that, in runners, PFP is mediated by increased joint loading, and is consistent with the findings of [PERSON] and [PERSON] [50], who found enhanced patellofemoral joint stress in those with PFP, using a mixed sample. The subset analyses from this study importantly revealed that enhanced patellofemoral joint stress in PFP runners was driven by female sex, as no differences were evident in males. The female PFP group exhibited more pronounced and coherent differences in patellofemoral joint loading, importantly highlighting potential sex differences in PFP aetiology. This emphasizes the need for different treatment approaches in male and female runners, and management strategies seeking to reduce patellofemoral joint stress are likely to be most efficacious in female runners. Patellofemoral joint loading is primarily caused by forces generated within the quadriceps [51]; therefore, enhanced patellofemoral joint stress in the female PFP group was mediated as a function of the corresponding increases in forces that were observed consistently across all four quadriceps muscles. A significantly more anterior footstrike position was shown in the control group in relation to the PFP group, which when contextualized via the strike index, revealed a rearfoot strike in the PFP group and a midfoot pattern in controls. The subset analyses again showed that this was mediated by female runners, and the chi-squared analyses support this, as significantly more rearfoot strikeers were shown in the overall and female PFP groups. [PERSON] et al. [52] showed that runners who habitually adopt a rearfoot strike pattern are more than twice as likely to experience a chronic running injury. Crucially, this investigation lends further precision to this observation, as in female runners the utilization of a rearfoot strike pattern makes runners significantly more likely to experience PFP. It is likely that the increased quadriceps muscle forces and patellofemoral loading shown overall and in the female PFP group were mediated by the rearfoot strike pattern adopted in relation to control runners. Utilization of a rearfoot strike pattern places increased demands on the knee extensors [53], and patellofemoral stress is greater in rearfoot strikeers [54]. From a clinical perspective, transitioning from a rearfoot strike pattern has been shown to attenuate patellofemoral joint loading and improve pain symptoms in male runners, although no such intervention has been undertaken in females [25]. Therefore, gait-retraining approaches that allow female PFP runners to modify their habitual footstrike pattern may be a particularly important clinical intervention. From a kinematic and temporal perspective, peak knee flexion and step length were lower in the PFP group, while knee flexion was lower in male symptomatic runners compared to females with PFP. Individuals with PFP experience reduced knee flexion [55; 56], which along with the reductions in step length may represent an attempt to minimise pain symptoms by mediating patellofemoral stress [49; 55]. Reduced knee flexion in both the overall PFP and male PFP runners may be indicative of kinesiophobia--a renowned complaint in patients with PFP [10; 56].