Vertical Jump: Biomechanical Analysis and Simulation Study

Abstract

Vertical jumping is a complex task requiring quick and harmonized coordination of jumper’s body segments, first for the push-off, then for the flight and lastly for the landing. The prime criterion for vertical jump efficiency is the height of the jump that depends on the speed of the jumper’s center of gravity (COG) in the moment when the feet detach from the ground. Besides maintaining the balance, the task of the muscles during the push-off phase of the jump is to accelerate the body’s COG up in the vertical direction to the extended body position. During the push-off phase of the jump, the jumper’s center of gravity must be above the supporting polygon that is formed by the feet (Babi et al., 2001). In contrast to the humans, today’s humanoid robots are mostly unable to perform fast movements such as the vertical jump. They can mostly perform only slow and statically stable movements that do not imitate the human motion. Besides, these slow and statically stable movements are energy inefficient. With the understanding of the anatomy and the biomechanics of the human body, one can find out that, beside the shape, majority of today’s humanoid robots and human bodies do not have a lot of common properties. To achieve a better imitation of the human motion and ability to perform fast movements such as the vertical jump or running, other properties and particularities, beside the shape of the body, should be considered in the design of the humanoid robot. Lower extremities of today’s humanoid robots are mostly serial mechanisms with simple rotational joints that are driven directly or indirectly by electrical servo drives. Such design of humanoid robot mechanism allows only rotational motion in joints to occur. This means that translations of the robot’s center of gravity are solely a result of the transformation of rotations in joints into translations of the robot center of gravity. Especially in ballistic movements such as fast running or jumping where the robot center of gravity is to be accelerated from low or zero velocity to a velocity as high as possible, this transformation is handicapped. The transfer of the angular motion of the lower extremity segments to the desired translational motion of the robot center of gravity is less effective the more the joints are extended. When the joint is fully extended, the effect of this joint on the translational motion of the robot center of gravity in a certain direction equals zero. Besides, the motion of the segments should decelerate to zero prior to the full extension to prevent a possible damaging hyperextension. Where relatively large segments which may contain considerable amounts of rotational energy are involved, high power is necessary to decelerate the angular motion.