Comprehensive description of sit-to-stand motions using force and angle data.

A normative description of a motion details the necessary and sufficient criteria to identify that motion. It equips researchers with a shared lexicon for describing their research and, in this way, adoption of a normative description facilitates communication within the research community. Although there is an abundance of descriptions of sit-to-stand movement, there is not a commonly accepted normative description of sit-to-stand; study-specific descriptions are commonplace. This work evaluates the breadth of existing sit-to-stand descriptions using new experimental data from 15 healthy young adults standing from a 46 cm chair. Our goal is to develop a normative description of the sit-to-stand motion that is in harmony with the literature. After aligning experimental data to seat-off (the one sit-to-stand event with a clear definition), events defining the start of sit-to-stand, seat-off, and the end of sit-to-stand are identified using a density-based clustering method. Then, the intermediary events of start of seat unloading, end of momentum transfer, and beginning of stabilization are determined while maintaining consistent sequencing and biomechanical meaning. These six events of sit-to-stand are determined from trunk, hip, knee, and ankle angle data and vertical ground reaction forces. The events are in greatest accordance with the descriptions of sit-to-stand introduced by Schenkman et al. (1990) and Kralj et al. (1990), and the event timings are in alignment with the findings of other researchers. The proposed description of healthy sit-to-stand promotes consistency in the description of this motion and adoption of this description will promote effective communication in sit-to-stand research.