## 4 Discussion  
The aim of the present study was to investigate the influence of different running shoe concepts with carbon fiber plates and different material properties on both physiological and biomechanical variables during a 10 km treadmill run. To provoke great influence on the examined parameters, shoes with different materials and geometries, but similar  
Figure 3: Comparison of shoe conditions for: (**a**) peak angular velocity (PAV); (**b**) maximum version velocity; (**c**) heal strike angle and (HSA); and (**d**) peak tibial acceleration (PTA). Significant differences between shoe conditions are marked with * (\(p\) < 0.05) and ** (\(p\) < 0.001). weights were used. We hypothesized that these distinctly different footwear conditions influence (a) biomechanical and (b) physiological variables. The biomechanical results show that the subjects adjusted their running style in response to the different shoe properties. Therefore, hypothesis (a) was confirmed. PAV (757.8 \(\pm\) 105.2 deg/s) and HSA (25.2 \(\pm\) 4.0 deg) were significantly lower in S1, compared to S2 and S3. In addition, evVel (552.1 \(\pm\) 162.2 deg/s) was significantly higher in S1 in contrast to the other shoes. Contrary to the mentioned parameters, PTA was not influenced by shoe conditions. In general, no significant differences were found for the biomechanical variables when comparing S2 and S3. It appears that running in the shoe with the highest midsole stiffness in the rearfoot and the lowest rearfoot height (Table 1) led to a distinct adjustment of the running style as a mechanism of shock absorption during the landing phase. The results HSA and PAV were consistent with the findings of [PERSON] et al. [44]. The authors found significantly lower values for the shoe with the flattest construction and the lowest cushioning. Additionally, [PERSON] et al. [45] also demonstrated that a shoe with thinner midsoles can lead to lower HSA due to reduced cushioning and subsequently to greater discomfort [46]. For evVel, a similar trend as in our study was found by other authors. For example, the lowest evVel for the shoe with the highest rearfoot cushioning and the highest evVel for the shoe with the hardest midsole was observed by [PERSON] et al. [47] when comparing six shoes differing in midsole hardness, and by [PERSON] et al. [40] when comparing three shoes with different midsole properties when running at different velocities. It seems that runners reduced HSA and PAV and increased evVel to protect the lower extremities from impact forces during the landing phase when running in flatter shoes with less cushioning. In the current study, this led to PTA values that were similar for all three shoe conditions. This is in contrast to most studies that found higher values for PTA or force rising rates (measured with force plates) when running in harder shoes [47; 48; 49]. However, most of these data were examined on short-term measurements on treadmills (<5 min), short outdoor tracks (<400 m), or based on only a few steps in the laboratory. In our study, subjects ran 10 km at 70% of their VO\({}_{2}\)max, and they had approximately 9 km to adapt their running style to each shoe condition to optimize the load on lower extremities. Therefore, longer runs may generate more realistic results. In contrast to the biomechanical parameters, no significant differences were found between shoe conditions for any physiological parameters. Therefore, hypothesis (b) had to be rejected. In this study, shoe conditions varied distinctly (Table 1) in terms of MBS, rearfoot and forefoot cushioning, as well as rearfoot and forefoot height. However, shoe mass was similar. Numerous studies have shown that different shoe characteristics, such as foam midsole material, MBS, and shoe mass, can influence running performance as well as biomechanical variables. Studies investigating the influence of shoe mass on physiological variables report lower energy consumption and better RE when running in shoes with lower mass [1; 50].