Summary
People move in complex ways, not just walking straight, and understanding how they keep balance during fast turns is tricky. The authors studied karate roundhouse kicks, which involve quick rotations, by looking at angular momentum, a measure of rotational motion. They found that kicks that were unstable had higher peaks of rotational movement before the kick landed and less slowing down afterward. The authors created new measurements based on angular momentum that help explain why some kicks are unstable, though different kicks can be unstable for different reasons. These measures might be useful for analyzing other dynamic movements or improving robotic walking.
What this means in practice
- •For robotics engineers: Improve robotic gait and balance control algorithms by incorporating angular momentum management insights from karate kicks.
- •For exoskeleton developers: Design smoother and more stable assisted walking motions in exoskeletons using new angular momentum-based measures from human motion analysis.
Authors
Jan C. L. Lau, Christian Mele, Jonathan Feng-Shun Lin, Katja Mombaur
Abstract
Human gait in reality extends beyond straight-line walking, with some situations even requiring drastic back-and-forth rotations. A smooth and stable execution may seem intuitive, but the underlying mechanics remains unknown. The Karate roundhouse kick may be an extreme case of exhibiting dynamic back-and-forth rotations, but investigating the angular momentum (AM) management can potentially inform stability analysis in dynamic human motions and smoother gait in robots and exoskeletons. This paper introduces two new AM-based measures and analyzes AM-related variables to study the target-less retractable back-leg Karate roundhouse kick. The purpose is to understand the underlying AM management, analyze the differences between stable and unstable kicks, and investigate how these variables and measures change over time with improvement. A one-year longitudinal study was conducted with the first author as a Karate student, and a Karate instructor was also recruited for one session as an expert, whose data is used for comparison. Results show that unstable kicks have higher peak total AM before Strike and smaller braking peak after Strike. The proposed AM-based measures are able to identify the cause of some unstable kicks, though no clear distinction could be made between stable and unstable kicks since kicks can be unstable for different reasons. Nonetheless, the proposed measures can be applied as performance measures to analyze other types of dynamic motions. To incorporate them as stability criteria, however, it is recommended to also consider their coordination with time, kinematics, and center of pressure.