Equilibrium and Stability of the Upright Human Body

We propose a new parameterization for describing forward and backward leanings of the straight human body with the feet fixed on the ground. During this motion stability of static equilibrium of the upright human body depends on the basic parameters such as coordinates XCG and YCG of the center of gravity of the body in the upright position and the radius R of the base of support. We introduce two coefficients k1= YCG/R and k2= XCG/R which are enough to calculate critical values of the angle α between the vertical axis OY and the axis of the cylinder the body is fitted into. We have calculated critical values αcr′ and αcr′′ when the body becomes unstable during leanings back and forward cor…