## 4 Discussion  
### Spatiotemporal Parameters  
Our findings revealed that walking uphill on progressively steeper slopes and at lower speeds was associated with significantly shorter steps and more outward foot rotation compared to level walking. Downhill walking, on the other hand, resulted in shorter and markedly wider steps compared to level walking (Figure 4). In terms of temporal parameters, step time increased, and cadence decreased during uphill walking conditions, whereas the opposite occurred during downhill walking conditions compared to level walking (Figure 5). Figure 4: Mean and standard deviation (error bars) of (**a**) step length, (**b**) foot rotation, and (**c**) step width under different walking conditions. The change in each spatial parameter for the uphill and downhill walking conditions is presented as a multiple of the corresponding mean spatial parameter in the C walking condition. Figure 3: Box plots for center of pressure (COP) positions in (**a**) anteroposterior and (**b**) mediolateral directions during uphill (+) and downhill (\(-\)) walking at speeds determined by [PERSON]’s hiking function. \({}^{\mathrm{a}}\) Significant difference (SD) compared to A walking condition (\(p<0.001\)); \({}^{\mathrm{b}}\) SD compared to A and B walking condition (\(p<0.001\)); \({}^{\mathrm{c}}\) SD compared to A, B and C walking condition (\(p<0.001\)); \({}^{\mathrm{d}}\) SD compared to A, B, C and D walking condition (\(p<0.001\)); \({}^{\mathrm{e}}\) SD compared to B walking condition (\(p<0.05\)); \({}^{\mathrm{f}}\) SD compared to B (\(p<0.01\)) and C (\(p<0.05\)) walking condition. The duration of the stance and swing phase, as well as the duration of the double-stance phase, increased during uphill walking but slightly decreased during downhill walking compared to level walking conditions (Figure 6). The differences in spatiotemporal parameters of gait observed during uphill and downhill walking could be attributed to mechanical/kinematic responses, physiologic adjustments, and sensory modifications that enable participants to cope with gravitational resistance during uphill walking and to manage excessive impact forces during downhill walking. Previous studies have shown that during uphill walking from 0 to 10%, there is a progressive forward tilt of the trunk and pelvis, accompanied by an increasingly flexed posture of the hip, knee, and ankle at initial foot contact [15, 47]. Conversely, downhill walking from 0 to -10% induces a progressive backward tilt of the trunk and pelvis, along with a decreasingly flexed posture of the hip at initial foot contact, as well as an increase in  
Figure 5: Mean and standard deviation (error bars) of (**a**) step time and (**b**) cadence under different walking conditions. The change in each temporal parameter for the uphill and downhill walking conditions is presented as a multiple of the corresponding mean temporal parameter in the C walking condition. Figure 6: Mean and standard deviation (error bars) of stance, swing, and double-stance phase duration under different walking conditions. The change in the duration of each gait phase for the uphill and downhill walking conditions is presented as a multiple of the corresponding mean gait phase duration in the C walking condition. knee flexion during weight acceptance and late stance [15; 47]. These kinematic responses may be partly responsible for the changes in step length, which, according to some researchers, explain its increase during uphill walking and its decrease during downhill walking [15; 47]. However, these findings contradict the results of the present study, as well as other research, which demonstrated a reduction in step length during both uphill and downhill walking [16; 17]. Differences between studies regarding step length may result from the speed implemented for walking on various slopes.