# Comparison of Gait Smoothness Metrics in Healthy Elderly and Young People
## 4 Discussion  
### Age Group Comparison  
The HR metric has been previously utilized in clinical studies to compare smoothness between healthy older adults and those experiencing cognitive decline [2]. [PERSON] et al. observed significant differences in the AP and V directions among tested groups. Individuals with cognitive impairment displayed lower HR values compared to healthy controls, suggesting that notable changes in HR are discernible even in the early stages of cognitive decline. The authors stated that monitoring trunk accelerations may facilitate the early detection of HR changes preceding alterations in walking speed. [PERSON] et al. similarly employed HR to assess smoothness in healthy individuals across two different age groups [3]. Their study revealed that younger individuals walked smoother than older counterparts, showing statistical differences in HR along the AP axis. This finding contradicts [PERSON] et al. [25], where no significant differences were observed. Moreover, the study concluded that age did not differentiate smoothness at varying walking speeds, affirming that younger individuals consistently exhibited smoother gaits than older individuals across all conditions. Figure 8: Smoothness of the acceleration signals along vertical (V), mediolateral (ML) and anteroposterior (AP) directions and acceleration RMS on the gait task performed by young group. (**a**) Normal vs. fast task implemented with LDLJ; (**b**) normal vs. fast task implemented with SPARC; (**c**) normal vs. fast task implemented with HR. * Specifies statistical difference in the comparison. Figure 9: Smoothness of the angular velocity signals along vertical (V), mediolateral (ML) and anteroposterior (AP) directions and angular velocity RMS on the gait task performed by young group. (**a**) Normal vs. fast task implemented with LDLJ; (**b**) normal vs. fast task implemented with SPARC; (**c**) normal vs. fast task implemented with HR. * Specifies statistical difference in the comparison. This study aimed to replicate [PERSON] et al. 's research and complement [PERSON] et al. 's findings by comparing young and older individuals, regardless of any disorders, to clarify whether aging alone affects smoothness, independent of cognitive impairment. Surprisingly, the results of this work concerning HR metrics during normal gait are characterized by controversial trends. Contrary to previous studies, the older individuals demonstrated smoother gait than the younger group across all signals analyzed, except for acceleration along the V direction and acceleration RMS, which align with prior research findings. According to this, during fast walking, statistical significance was only found in acceleration along the V axis and acceleration RMS, with outcomes in line with the literature. In this scenario, younger individuals exhibited smoother gait compared to older adults, consistent with previous findings. All in all, the HR index did not indicate a direct association suggesting that age affects gait smoothness similar to the onset of cognitive impairment at the moment; however, HR calculated on acceleration along the V direction and acceleration RMS may deserve further investigation. Additionally, [PERSON] et al. employed LDLJ and SPARC metrics to assess differences between young and older individuals with good health conditions during gait and stair negotiation, collecting gait signals using a stereophotogrammetric system [16]. No between-group differences were noted for walking or stair ascent. However, the LDLJ metric indicated that the older adult group performed stair descent less smoothly than the young adult group in all directions of acceleration. Our study findings demonstrated that during normal speed gait, LDLJ metrics showed differences in smoothness between older (less smooth) and younger individuals (more smooth) across all investigated signals.