Inertial accelerometer sensors record movement. Rhythmic and repetitive movement is common to almost all sporting activities. It is possible to model the dynamic acceleration of a swing (both body and implement) using a cosine squared function of angular position with time. In cricket, a straight drive using a bat mounted accelerometer can be well matched (r > 0.9) and the time and effort determined. The same analysis can be applied to baseball, field hockey, boxing and running. As the function is symmetrical, situations where the acceleration time is different to the deceleration time can be readily identified. In most cases both the acceleration and the deceleration require muscle effort and control.