Abstract:
Running shoes are important to runners as they can help reduce injury in runners. In this study, we wanted to find the changes of stress in patellofemoral joint in worn out shoes. The study was divided into three projects. The first project pertained to the building and development of a running simulation machine (RSM), which was looked like a cartwheel. The RSM was designed and calibrated to mimic running mechanic of female runners weighted between 55-58 kgs. The RSM was calibrated such that vertical ground reaction forces at impact peaks and active peaks, foot contact time, patterns of weight distribution, and the movement of center of pressure produced by RSM was similar to those produced by actual running. After the first project, the objective of the second project was to study the shock absorption capability (SAC) in worn out running shoes. In this study, nine female runners were recruited to the study. The participants were asked to wear EVA midsole running shoes, which were made deteriorated over 800 (8×100) kms. Vertical ground reaction forces (VGRFs) and SAC were measured from the force plate and F-scan before and after each 100-km. SAC was calculated as the difference between VGRFs measured by force plate and F-scan. One way ANOVA with repeated measures were used to analyse the data. The results showed that new running shoes could absorb 70% of body weight, and SAC of running shoes were statistically different over running distances. SAC decreased as running distances increased. A post hoc analysis suggested that 300-km was a critical running distance after which SAC decreased markedly. At 300 kms, running shoes could absorb only 60% of body weight or around 35% of impact force. The final project found the changes of stress at patellofemoral joint (SPFJ) among worn out shoes. The stress could be found from the model suggested by Roos et al. (2012), and the knee moments were found using inverse dynamic technique. The results showed that as running distances increased, SPFJ also increased, where at 800 km, SPFJ was 20% greater than SPFJ found in new shoes. However, SPFJ found in the study was lower than critical stress causing injury reported by other papers. In this study, the average SPFJ at 800 km (which was the maximum SPFJ) was 10 MPa