Humans Use Similar Posture Sequences in a Whole-Body Tracing Task

Humans have elegant bodies that allow gymnastics, piano playing, and tool use, but understanding how they do this in detail is difficult because their musculoskeletal systems are extremely complicated. Previous studies have shown that common movements such as reaching for a coffee cup, cycling a bicycle, or playing the piano have common patterns across subjects. This paper shows that an arbitrary set of whole-body movements used to trace large closed curves have common patterns both in the trajectory of the body's limbs and in variations within those trajectories. The commonality of the result should spur the search for explanations for its generality. One such principle could be that humans choose trajectories that are economical in energetic cost. Another synergistic possibility is that common movements can be saved in segments that can be combined to facilitate the process of deployment.