BIOMECHANICAL LOADING OF THE AMERICAN KETTLEBELL SWING

摘要

The American kettlebell swing is a variation of the Russian kettlebell swing where the kettlebell is swept in an arc from between the legs to an overhead position with straightened arms. Previous studies involving the kettlebell swing have examined the aerobic and cardiovascular impact of the swing, the variation of mechanical impulse and power generation with kettlebell weight, and compared its efficacy to other types of exercises. However, there have been limited studies examining the dynamic biomechanical loads of the swing on the arm and shoulder. The aim of this study was to establish the mechanical demands of the American kettlebell swing exercise on the arms and shoulders to determine the regions of highest force output and the variation of the forces throughout the swing, all based on percentage of the swing completed. In order to obtain kinematic data, two female subjects with prior kettlebell exercise experience performed one set of fifteen American swings with 8kg and 12kg kettlebells. Position and orientation data was recorded during trials for the kettlebell, joints, and centers of mass of arm segments. Velocity and acceleration data was found using finite-difference approximations. An inverse dynamics method applied to (2-D) planar motion using Newton-Euler equations was used to determine the forces and moments at various joints along the entire arm including the wrist, elbow, and shoulder joints. Data was time normalized as percent of swing, where 0% and 100% indicated the beginning and end of the swing respectively, and approximately 50% denoted the transition between upswing and downswing halves. Results revealed that the arm was under tension during 0% to 35% and 67% to 100% of the swing, indicating the upper torso works to provide the normal force to support the curved motion of the kettlebell. During 36% to 66% of the swing the arm muscles worked in order to support the weight of the kettlebell over the head. While the lower extremity mechanical demands associated with kettlebell swings have been studied, the current results help clarify the upper extremity mechanical demands associated with kettlebell swing exercise. The results of this analysis will better help practitioners to understand the prerequisite upper extremity function needed to perform the full American style swing. The American kettlebell swing carries risks its Russian equivalent does not have, typically breaking form to make the shoulder extension involved with raising the kettlebell above the subjects head. These results suggest that the extra range of motion in the American kettlebell swing prompts different mechanical demands which, in turn, targets different muscle groups from the lower half of the American swing or the Russian kettlebell swing. Finally, because increasing mechanical stimuli is an important component to exercise progression, this analysis fills the void of understanding the effects of changing kettlebell loads on the upper extremity demands. Future research will consider the symmetry of the upper extremity mechanical patterns revealed by this analysis.