The real rotational capacity of the human joints - the muscular and gravitational torques and the foot as a platform.

Abstract

Purpose: The purpose was to answer what is the relationship between torques acting on the human body, how does the triceps calf muscle balance the weight of a tilted body and what is the foot's role in the titling body? Methods: Two research models were developed. Model 1 - the one-sided lever system consists of a flat bar with, an axis of rotation, used to determine the weight and torque at a given point on it. Model 2 - the two-sided lever system consists of a flat bar imitating a tilted body counteracted by the Achilles tendon, and a platform imitating a foot. The centre of gravity was determined without considering "the foot". Results: When the centre of gravity of the human body tilts, the foot does not participate in the tilt of the rest of the body, because it tilts on the axis of rotation of the upper ankle joint, and not on the plantar side of the foot. The further the point of gravity is from the axis of rotation, the smaller the weight, but the moments of gravity are the same. The apparent weight loss when lifting it with one-sided support (getting up from a squatting position) is a real decrease in the gravitational moment and the lifting moment counteracting it. Conclusions: When analysing human biomechanics, focusing on real rotational force (not only the forces of muscle and gravity) is necessary (muscle moments balancing gravitational moments). The research may help develop effective rehabilitation methods, surgical procedures and sports training.