Bernstein, a Russian physiologist in 20th century, aka, the father of biomechanics, reported that skilled blacksmith correctly hit a target place by the hammer, however, variance was observed in hand trajectory every trial.
From this finding he discussed that (1) our nervous system pays attention to some specific points to perform a given task and (2) the ability to solve a given task by multiple ways, in other words, by utilizing the synergy among the abundant DOFs, is a typical characteristics of the intelligence that the living bodies show.
This episode indicates that variance of the movement of proficient performers involves a key to find tacit knowledge. We are analyzing such tacit knowledge involved in human movements by using uncontrolled manifold (UCM) analysis.
In our laboratory, we analyzed many movements such as walking by the UCM analysis. In the case of walking movement, we found that the foot height at the moment of minimumt toe clearance (MTC) and the hip height during double support phase are well adjusted by the cooperation among leg joints.