## 4 Discussion  
The purpose of this study was to identify biomechanical measures related to GRF associated with ITBS in runners. Our main hypothesis was that a subset of aspects of GRFs would correctly classify participants with ITBS, was confirmed. Patterns of interaction involving PGRFI, AGRFI, AGRFP, and VSIL identified runners with and without ITBS. The model presented good performance, with a total correct classification of 83.3%, and good accuracy, with an area under the ROC curve of 0.87. Using a non-linear model that accounts  
Figure 2: ROC curve for ITBS in runners. The area under the ROC curve was 0.87 (\(p<\) 0.001). ROC, receiver operation characteristic. \begin{table}
\begin{tabular}{c c} \hline \hline
**Risk Profiles** & **PR (95\% CI)** \\ \hline
**Node 3** & \\ Posterior Ground Reaction Force Impulse \textless{}= 0.019 BW*s & - \\ Anterior Ground Reaction Force Impulse \textless{}= 0.012 BW*s & \\
**Node 6** & \\ Posterior Ground Reaction Force Impulse \textless{}= 0.019 BW*s & \\ Anterior Ground Reaction Force Impulse \textgreater{} 0.012 BW*s & \\ Anterior Ground Reaction Force Peak \textgreater{} 0.22 BW & \\
**Node 8** & \\ Posterior Ground Reaction Force Impulse \textless{}= 0.019 BW*s & \\ Anterior Ground Reaction Force Impulse \textgreater{} 0.012 BW*s & 2.25 (0.50 to 9.99) \\ Anterior Ground Reaction Force Peak \textless{}= 0.22 BW & \\ Vertical Stiffness at Initial Loading \textgreater{} 76.97 kN/m & \\ \hline
**Prolective Profiles** & \\ \hline
**Node 2** & 0.14 (0.02 to 0.72) * \\ Posterior Ground Reaction Force Impulse \textgreater{} 0.019 BW*s & \\ Anterior Ground Reaction Force Impulse \textgreater{} 0.012 BW*s & \\ Anterior Ground Reaction Force Peak \textless{}= 0.22 BW & \\ Vertical Stiffness at Initial Loading \textless{}= 76.97 kN/m & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Risk and protective profiles for ITBS (n = 60). for interactions between GRF variables may help to explain why prior research has found inconsistent results of GRF in runners with ITBS. Prior work did not find differences in loading rates or vertical stiffness using a partially overlapping population of runners with ITBS [22]. Two studies did not find differences in antero-posterior peak forces [19; 21]. In addition, inconclusive results were found for vertical and braking forces; one study showed higher vertical and peak braking forces [23], while the other showed only lower peak braking forces [18]. Unfortunately, no studies have presented data on GRF impulse values. To our knowledge, this study is the first study to assess the interactions between biomechanical factors related to GRF and ITBS in runners using a complex approach. A single study has used a CART analysis to identify profiles that classified runners with Achilles tendinopathy, using aspects of the hip and foot, including range of motion and strength measures [33]. Other studies with CART, identified interactions between clinical aspects and anterior knee pain in mountain bikers [34], re-injury of the anterior cruciate ligament in soccer players [35], and persistent shoulder pain in non-athletes [31]. Interactions between anteroposterior forces and vertical stiffness were associated with ITBS occurrence. Each of these factors were associated with RRIs and patellofemoral pain [18; 22; 23; 36]. It can be suggested that interactions between anteroposterior forces and vertical stiffness may be more relevant for some injuries than others. In addition, loading rates or mediolateral forces were not associated with ITBS when analyzed individually or through a complex approach [18; 22; 23]. These findings suggest that these aspects do not play a role in this condition. Despite the correct classification and accuracy of the model, the small differences in runners with and without ITBS, and the low cut-off points, may limit the relevance of our findings in application to clinical practice of managing runners with this condition.