Extraction and difference quantification of protective motion in case of indoor infant fall behaviors by multivariate analysis

Fall-related injuries are one of the most common injuries in daily life. Occasionally, particularly in children and the elderly, fall accidents can lead to fatal injuries. Therefore, it is necessary to clarify the mechanism of human falls and to develop a method to prevent such accidents. In previous studies, many researchers have estimated fall-related injuries, such as bone fractures, using the finite element method or a dummy. However, to adequately evaluate fall injuries, the pre-injury phase (such as avoidance or protective reactions) should be evaluated, because impact forces are related to such reactions and their ineffectiveness may be the main cause of falls in children. Therefore, in this study, infants’ protective reactions were focused on as a first step in analyzing the pre-injury phase. The natural fall behaviors of 16 infants measured in a lab imitating a living room environment were captured. Then, the joint angle data were analyzed to extract the special features of fall behavior and determine the time at which the protective reaction starts. The special features of fall behavior such as the parachute reflex were extracted using the principal component method. In 12 out of 16 cases, the start time of the protective reactions was extracted using the singular spectrum conversion method. Then, the durations of protective reactions and skill of protective reactions were defined using principal component analysis. Using these definitions, we propose an evaluation method for the effectiveness of protective reactions in different fall behaviors.