A study on estimating the center of gravity velocity using lower limb joint power during squatting

Abstract

This paper presents a proposed method for center of gravity (COG) velocity estimation during squatting using information obtained from lower limb motion measurements. A squat exercise uses the lower limb joints and the muscles around these joints. The squat exercise velocity changes according to the lower limb muscle activity. Some earlier reports of relevant studies have suggested that muscle weakness and neurological deterioration influence the COG velocity when standing up. Therefore, it is important to clarify the relation between the COG velocity and lower limb motion for efficient training and the prevention of falls among older people. For this study, we constructed a squat velocity model that represents the relation between the COG velocity and lower limb joint power during squatting. Although no joint power indicates each muscle activity in detail, it is possible to estimate muscle activities around the joints approximately by using the joint power. For this experiment, the squat exercise was measured using a 3D motion analysis system. The experiment was conducted for three stance widths. The COG velocity and the lower limb joint powers were calculated using information from the 3D motion analysis system. We estimated the squat velocity model parameters by application of Kalman filter using the measurement information. The analysis results for the squat velocity model indicated a quantitative relation between the COG velocity and the lower limb joint power during squatting. Furthermore, comparable results were obtained from three stance widths. This analytical method is anticipated for use in evaluation of motor function and exercise assisting device design.