Three-dimensional biomechanical analysis of fast bowling in cricket
A three-dimensional (3-D) dynamics model of the human body has been developed to provide a mechanical basis for evaluating fast bowling technique. Thirty-four fast bowlers were selected for study and divided into four groups according to ball release speed. A five camera 240 Hz motion analysis system (Motion Analysis Corp.) was used to track markers on the bowler delivering a series of balls at a target in line with the wickets, and a Bertec force plate was used to measure ground reaction forces. The marker arrangement allowed for the 3-D motion tracking of all major body segments. The resulting kinematic and force plate data of a typical ball were fed into a computer model using Mathematica's Mechanical Systems Pack. This is a set of packages designed for the analysis of spatial rigid body mechanisms by implementing a dynamics formulation with Lagrangian multipliers. The computer model gives a 3-D representation of the human body as a system of fifteen rigid body segments with mass and inertia properties. The model can output the kinematics, inverse solution dynamics, kinetics and powers for each body segment of a bowler delivering a ball. Bowling in cricket is a unique method of propelling a ball at high speed so that it reaches a batter 20 m away after having bounced once off the pitch. Fast bowlers reduce the time available for the batsman to execute the correct stroke, and therefore increase the chance of error. There are a number of coaching texts available that propose various hypotheses on the correct technique of fast bowling, which have been mostly based on the experiences of successful fast bowlers. However, dynamics has not played any meaningful role in the development of fast bowling technique. In this thesis, the synthesis of a 3-D rigid body model of bowling was used to calculate the inverse solution dynamics, kinematics, kinetics and segment power flows to test certain established hypotheses on the mechanics of bowling technique. The analysis also probed for mechanical differences in technique between bowling speed groups. It was found that lower trunk, upper trunk, bowling arm, front arm, front leg, and rear leg interacted in such a way that each segmental motion was subject to a kinematic sequencing pattern and a dynamics actuation pattern determined by the calculation of muscle powers. Also, it was possible to differentiate between the consequential motion of a segment, and the actuation of a segment motion. This information provides a perspective of how the body needs to move in order to achieve correct technical form. The results show that that certain established concepts of bowling technique, such as front arm 'sweeping' and 'pull down', lower trunk flexion, and rear leg action have only been partially specified. Also, in certain technical and sequencing aspects there are differences between the bowling speed groups.
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