The effect of moment of inertia on the speed of swung implements.

The maximum swing speed of an implement is an important performance parameter in many sports. It is understood that moment of inertia (MOI) has an effect upon the swing speed of an implement and numerous studies have found a similar rate of swing speed decay (n). These studies considered different movements which suggested that skill was less important than physique to the relationship between swing speed and MOI. The aim of this project was to quantify this relationship and to determine whether the physical characteristics of a participant can be used to predict their swing speed performance. A series of eight visually identical rods with varied MOI were swung in a heavily restricted, maximal motion and trials were recorded with a motion capture system. The results found that swing speed decreased as MOI increased. It was also found that if n was assumed to be constant, the maximum work done by a participant was strongly and significantly related to their swing speed. The relationship between work done and swing speed was used to create a model to predict swing speed for an implement with a specific MOI. This model was validated for a new set of participants performing the same restricted motion and all measured data fell within the confidence intervals of the predictions. The ecological validity of the model was tested in an analysis of the swing speed of tennis groundstrokes. An impact model was used to analyse the effect of changing MOI on ball speed. It was discovered that there is an optimum MOI that produces a maximum ball speed and that this optimum MOI is dependent upon n. This makes the customisation of equipment a realistic possibility. A simple method for measuring n in a non-laboratory environment is proposed that will enable the customisation process to take place.