## 4 Discussion
### Gait Adaptation According to Cognitive Function Decline  
The LC group had a slower walking speed, longer DLS and shorter SLS, compared to the NC group. As mentioned in Section 4.1, this difference results from the change in the ratio of the LR and the MST and the difference in the motor control pattern. This gait, as exhibited by the LC group, may be an adaptation to further ensure gait stability. In DLS, including LR and PSw, the movement speed of the center of mass (COM) is the fastest. At this time, if the push-off function increases while pAA-2 decreases, the COM movement will be further accelerated. If the movement speed of COM is further accelerated, lower limb collapse may be induced during the first half of the stance phase, as inferred from the low support moment of the LC group. However, in the LC group, pAA-2 increased and mAEM decreased during push-off. That is, as dorsiflexion increases, the upward and forward acceleration of COM decreases, and as the plantar flexor moment decreases, forward propulsion through the push-off decreases. There was also no difference between the two groups in PAA-3 and AAD-2. This means that no extension occurred to counter the more flexed ankle joint. If extension occurs, as mentioned earlier, the COM accelerates further forward and upward, resulting in a higher movement speed, which can lead to instability. This may be supported by pAP-4, which shows that the energy generation for forward propulsion through extension is low. The shorter SLS of the LC group is due to the reduced MSt proportion. In the MSt, while one leg supports the body, the body moves forward and an upright stand alignment of segments of the supporting leg is achieved. At this moment, the supporting leg must support the body while maintaining postural balance. The shorter MSt of the LC group would be a strategy to reduce this phase to induce double limb support quickly, thereby securing gait stability. This gait adaptation of the LC group is consistent with the gait changes that occur with aging. Several studies [21; 25; 26] related to gait in the elderly have reported that walking speed slows, DLS lengthens, and SLS shortens with age. However, there was no statistical difference in age among the subjects who participated in this study. Thus, the differences shown by the LC group were due to the level of cognitive function, not age. In other words, this suggests that the lower the cognitive function, the more trying it is to secure the stability of gait. Perhaps this gait adaptation is due to lower postural balance or lower quadriceps/biceps femoris function. First, there are many studies reporting a positive association between decreased cognitive function and decreased vestibular function [27]. The vestibular sensory function, as is well known, is the main sensory system that regulates postural balance. An adaptation of the LC group may be the result of a low vestibular sensory function. Therefore, in future studies, it will be necessary to investigate vestibular sensory function in the subjects who participated in this study and to reveal its relationship with gait adaptation. Second, as shown in Figure 1, pKM-1 and mKEM were lower in the LC group than in the NC group. In addition, the knee extensor power is low during the LR to MSt. Furthermore, the support moment was significantly lower in the LC group than in the NC group, indicating that this difference is due to the knee extensor. That is, it can be inferred that the ability of the knee extensor to support the body while maintaining balance with the single lower extremities was lower in the LC group. These results can suggest clinical evidence that knee joint muscles should be trained/supported when performing walking exercises, to protect against progression to dementia, and to assist gait in the daily life of elderly people who suffer from cognitive decline. To further confirm this, further studies analyzing EMG are needed.