## 4 Discussion  
The purpose of this study was to investigate the spatiotemporal, kinematic, and kinetic parameters of the leading limb during walking, PGT, and UGT to comprehend the mechanism that prepares and generates the braking force during the pre-stopping, initial stopping, and terminal stopping phases. Our results showed that both planned and unplanned stopping were similar to usual walking in terms of the spatiotemporal parameters. An exception to this occurred between PGT and UGT. In our results, the GT time during the PGT trial was greater than that during the UGT trial, which may be due to the pre-informed foot positioning of where to stop in the PGT trial [10; 24]. The subjects were asked to stop with their feet parallel to a designated force plate during the PGT trial. However, it was rare to keep the feet parallel in the UGT trial. A previous study has shown that planned stopping takes approximately 0.5s longer than unplanned stopping because of the additional time required to place the feet parallel [24]. However, in our study, the GT step length during UGT was greater than that during PGT. This difference may be attributed to the effective control of the COM to acquire dynamic stability during the PGT and UGT trials. In a previous study, when gait was terminated due to an unexpected stimulus, the body absorbed the sudden increase in the GRF and showed gait termination with a long stride length as a reaction to control the movement of the COM [25]. Therefore, it is thought that the braking force was applied by increasing the stride length to stop while maintaining stability in response to the unexpected stop signal because of the lack of a pre-informed stopping point in the UGT condition in our study. In this study, we subdivided gait termination into three phases based on previous studies to compare the differences in kinematic and kinetic parameters between gait conditions [2; 26; 27]. Phase 1 consisted of the last stride prior to stopping, from heel contact of the trailing limb to maximal advancement of the mid-stance, where propulsive force occurs in stance phases. In this phase, the leading limb enters the pre-swing, initial swing, and mid-swing phases, which involve lifting the foot off the ground, moving forward, and accelerating the swing [28]. The swing limb is not only rapidly accelerated forward by ankle plantar flexion during the pre-swing to generate propulsive force but also rapidly accelerated forward by ankle dorsiflexion during the initial swing, increasing the angular velocity to advance [28; 29]. During Phase 1, there were no significant differences in the hip and knee ROM between the gait conditions, except for the ankle ROM. In addition, the ankle ROM was significantly lower in the PGT trial than in the UGT trial. These results can be explained by the decrease in propulsive force at gait termination in response to a stop signal [18; 30]. According to the reported literature, for this time, a 10% reduction in gait velocity was observed in the PGT trial, and the period of generating propulsive force was reduced compared with walking. In the PGT condition, participants exhibited lower peak plantar flexion during pre-swing and less dorsiflexion after toe-off, compared to the UGT condition [31]. This strategy decelerates advancement by decreasing dorsiflexion during the swing phase [32; 33]. Therefore, in the PGT condition, the ankle joint is considered to predominantly contribute to deceleration in the initial preparation for generating the braking force [32; 33]. In contrast, in the UGT condition, the subjects had to respond to an unexpected stop signal during Phase 1. When unexpected stimulation forces the body to stop walking suddenly, dynamic stability is disrupted because it does not have enough response processes [34; 35]. Subsequently, the ankle joint during this period would not be successful in generating braking forces owing to instability and disturbing kinesthetic control [19; 34; 35].