## 4 Discussion
During impact (IFC-MS), the second largest effect on peak RES accelerometer accelerations was observed at the pelvis segment (F value = 58.0, Figure 1). Increased hip flexion at IFC, which also supports previous findings [19], reduces the effective mass of the pelvis segment [12], causing increased linear (anterior) and angular (internal rotation) peak velocities during impact (IFC-MS) (Figure 1). This results in increased flexion of the pelvis at MS due to the pelvis decoupling to support the deceleration of the trunk segment post-impact as it supports trunk stability. During propulsion (MS-TFC), there are medium-sized effects of pelvis angular (extension and internal rotation) and linear (anterior) peak velocities, which contribute to larger RES and VT peak accelerometer accelerations (Figures 1 and 2). Conversely, reduced extension peak velocities (increased flexion) at the pelvis contributed to larger AP peak accelerometer accelerations, and greater frontal plane peak velocities at the pelvis resulted in larger ML peak accelerometer accelerations (Figures 3 and 4). This indicates that insights can be gained into pelvis extension and stability properties of athletes by analyzing the differences between VT, AP and ML peak accelerometer accelerations. Furthermore, similar differences between the peak accelerometer accelerations were also observed regarding the thorax segment velocities. Reduced peak linear (anterior) velocity during impact and increased peak linear (vertical) velocity during propulsion of the thorax resulted in larger VT peak accelerometer accelerations (Figure 2). Whereas increased linear (vertical and anterior) peak velocity during impact and increased linear (lateral) peak velocity during propulsion of the thorax resulted in larger AP peak accelerometer accelerations (Figure 3). As force is transferred from the pelvis to the trunk, the surrounding musculature is activated to maintain stability and influences the subsequent displacement of the trunk segment [25]. Therefore, our results suggest that analyzing the differences between the VT and AP peak accelerometer accelerations may provide insights into these mechanisms. Findings from this study show that GRF attenuation properties of the surrounding joints to the shank segment and the kinematics of the pelvis in maintaining trunk stability, specifically at MS, have the largest effects on the peak accelerometer accelerations. Practical applications of these findings are that peak accelerometer accelerations could be valuable in analyzing an athlete's rehabilitation from an ACL reconstruction, as this has been shown to affect knee extension during running [36]. Alternatively, observing the differences between the axis of peak accelerometer accelerations throughout an athlete's training session may be used to provide insight into the level of neuromuscular fatigue affecting the stability of pelvis/trunk segments [37; 38]. While a direct comparison of our results to those of [PERSON] et al. (2014) was not possible due to the differences in statistical analysis between the studies, similar findings were observed regarding the significant effects of the hip and knee flexion/extension angle on the RES acceleration profile at IFC (Figure 1). The present study utilized GLMMs as repeated measures were present, whereas [PERSON] et al. (2014) employed a stepwise regression analysis. [PERSON] et al. (2014) mounted their accelerometer on the lower trunk. Therefore, it can be suggested that hip and knee kinematics at IFC affect both the lower and upper trunk acceleration profiles. In addition, our results refute previous suggestions [22] that the mounting site of the accelerometer on the upper trunk is unacceptable for observing changes in lower limb running kinematics. The limitations of the present study are that the findings only apply to straight-line running, as the trials were conducted on a treadmill.