## 4 Discussion
Although there were differences in inclusion and exclusion criteria, the authors included some of the same articles of the current study [29; 30; 33; 34; 35; 38; 39]. The results mainly show an increased SF, shorter ST and AT, and similar CT for all inclinations [5]. However, the research conducted by [PERSON] et al. [37], which has stirred up a lot of controversy regarding the kinematics of downhill running, was not previously considered. Moreover, studies that contained analysis on inclinations greater than 20% were also included [47] as well as running individual velocity for each runner based on the athlete's aerobic abilities [9]. The current study has several limitations, which are related to the testing procedures used by the various authors. First, it is important to mention the different velocities and inclinations in the tests performed. Another distortion is the test execution time varied, which ranged from tens of seconds to tens of minutes. Despite the moderate velocity in all the included studies, prolonged exertion can cause fatigue and distortion of time and space parameters. Indeed, in a study by [PERSON] et al. [48], a similar direction of change for SF was observed even for extremely high velocities (4.7 m/s or 5 m/s). Similar results were presented by [PERSON] et al. [49], who also showed fatigue-induced changes in lower limb kinematics and kinetics. [PERSON] et al. [50], analyzing kinematic parameters during a 4 km race, also found that as distance and fatigue increased, a decrease in stride length, step frequency, and foot contact time was shown. Analyzing the results of the above authors, there is a risk that prolonged trials, even at moderate intensity, can alter running kinematics. Another factor that may have affected the reliability of the results was the use of different testing tools using different measurement technologies. Differences in spatiotemporal parameters can be small, so the use of different technologies could affect the results obtained. For the same reason, the sample size of 9-25 participants may be too small for reliable statistical analysis. In order to achieve the desired effect, the sample size should be larger and verified with statistical tools. Another factor limiting the objectivity of the study is the lack of genders in the results obtained. Some authors specified the number of males and females in the study group, but the results were ordered holistically, considering both sexes. The study by [PERSON] et al. [50] observed significant differences for males and females in stride length and ground contact time. The differences for spatiotemporal parameters may be the result of significant differences in the biomechanics of the hip, knee, or ankle joint, which were noted in turn by [PERSON] et al. [51]. In running with different inclinations, these differences could be just as noticeable, which significantly affects the results obtained. Underestimation of the results may also have caused a moderate risk of bias, which amounted to 53.3% [30; 31; 32; 33; 34; 35; 39; 41]. However, it is worth emphasizing that the ambiguities affecting the evaluation of the mentioned papers were due to the lack of specific information regarding the confounding factors in the study and not to methodological mistakes. The included studies were characterized by a refined strategy and, above all, a meticulously prepared research procedure. Therefore, the high percentage of risk of bias should not significantly affect the accuracy of the individual authors' results. Even though the current study summarizes valuable information for coaches and practitioners on running kinematics. Some of the spatiotemporal parameters show wide variation depending on the inclination, velocity, or study procedure. Regarding some parameters, the authors do not agree on the direction of change in spatiotemporal parameters as determined by an increase or decrease in inclination.