Does the hip reflect the centre of mass swimming kinematics

The purpose of this study was to determine the relationship between the hip point and the cen- tre of mass for kinematical parameters (displace- ment, velocity and acceleration) in the three axes of motion. One complete stroke cycle was ana- lyzed in eight swimmers performing a 25 m front crawl swim test at high intensity. Within-subject correlation coeffi cients were computed between the centre of mass and both hips, as well as mean of the errors, RMS error and a paired sample t- test. High correlation coeffi cients were found for the displacement in the horizontal direction (r = 1.00 for both hips) and low to moderate cor- relation coeffi cients (r = − 0.01 to r = 0.54) were found for all other studied variables. Moreover, moderate to large RMS errors were observed: (i) between 0.05 and 0.15 for the displacement; (ii) between 0.16 and 0.30 for the velocity and (iii) between 5.28 and 7.86 for the acceleration. Complementarily, RMS errors for the intracyclic velocity variation were between 0.07 and 0.18. Considering the centre of mass and hip values statistical diff erences were found in velocity in x, acceleration in x and y, and intracyclic veloc- ity variation in y axes. Therefore, results suggest that the hip point does not represent most kin- ematical parameters of the estimated centre of mass in front crawl swimming.