## 4 Discussion
We assume, that this variation is related to the random differences in passing speeds among runs of the Sham and SCI animals over the CatWalk \(\mathrm{XT^{\textcircled{\tiny\textregistered}}}\) walkway, which we noticed when acquiring these data. Compared to the average speed parameter, the swing speed is a single-limb based CatWalk \(\mathrm{XT^{\textcircled{\tiny\textregistered}}}\) parameter designed with less variation between animals, regarding absolute velocity [23]. Accordingly, the correlation of the swing speed with the other measurements in our study was considerably higher (HL swing speed vs. BBB: \(r=0.73\), FL swing speed vs. preserved tissue: \(r=0.98\), HL swing speed vs. preserved tissue: \(r=0.84\)). The ability of the CatWalk \(\mathrm{XT^{\textcircled{\tiny\textregistered}}}\) gait analysis system to assess a variety of single paw/print parameters is seen as one of its major advantages as a behavioral test in preclinical SCI research. Thereby, the print intensity, the print area (including print width and length) as well as the maximum contact area are key parameters described in multiple SCI-related studies [22; 51; 52]. The CatWalk \(\mathrm{XT^{\textcircled}}\) parameter print intensity measures the stepping pressure, directly reflecting the weight bearing as a part of the locomotion function, while the print area indicates the relative force during locomotion. What is more, an increased print intensity or area has been attributed to improved fine motor digit function and trunk stability [20; 21]. Accordingly, in our study, the print intensity parameters, compared to the print scale parameters, reflected an earlier onset of spontaneous recovery after SCI, and had a better correlation with the percentage of preserved tissue (Figure 9). However, their correlation with the BBB open field scores was generally poorer. While this inconsistency is difficult to explain, it might be associated with the fact that the BBB open field rating scale is not a linear-based system, in which each different point has a significantly different meaning. Our current results, therefore, underline that the print intensity parameters might have a better capability to discriminate the level of spontaneous recovery after a cervical contusion/compression SCI. This notion might be supported by findings that showed a correlation of decreased print intensity with increased mechanical allodynia in rodent neuropathic pain models [51; 52]. Researchers have been seeking more objective methods to assess rodent locomotor function by integrating the results of different behavioral tests. To this end, linear regression analyses have been used to explain the relationship between different measurements in several studies: [PERSON] et al. created a scaling system to assess locomotor recovery in an impact SCI model at the T11 level in mice, which they named \"Combined CatWalk \(\mathrm{Index}\)\", by combining all 104 CatWalk \(\mathrm{XT^{\textcircled}}\) parameters into a single score. They used linear regression analyses to assess the relationship between the CatWalk \(\mathrm{XT^{\textcircled{\tiny\textregistered}}}\) parameters and Basso mouse scale open field scores and stated that the resulting \(\mathrm{R^{2}}\) values represented the \"power\" of the correlation [53]. Moreover, to evaluate the sensitivity of different behavioral tests after a dorsal hemi-transsection SCI model in rats, [PERSON] et al. aimed to correlate results from e.g., the tape removal test, the rope crossing test, the horizontal ladder, and the inclined rolling ladder with the CatWalk \(\mathrm{XT^{\textcircled{\tiny\textregistered}}}\) gait analysis using linear regression analyses as well [54]. However, from a statistical point of view, linear regression analyses which are typically used for prediction and not for correlation might not have been the best approach in this context, because the relationship between the CatWalk \(\mathrm{XT^{\textcircled{\tiny\textregistered}}}\) parameters and other measurements can at least not be deemed causal.