Hips & Trunk Rotation is Key... The kinematics study of the tennis forehand takes many factors into account; the joint angles are recorded prior to impact as well as at impact. The peak joint angle velocity is also recorded both before and after impact has occurred. The results of a study--Tennis forehand kinematics change as post-impact ball speed is altered—by Seeley and colleagues (2011) shows that as the ball speed increased at post impact the angular velocities at impact will also increase. The study also shows that the rotation of the player’s shoulders would increase disproportionately more compared to other kinematic measures (Seeley et al., 2011).