The ballistic movement is defined as a rapid voluntary movement which is motor programmed and in which visual feedback for path correction is not possible. A discrete ballistic movement is of short movement duration (less than about ZOO msec) uith a triphasic pattern in the electromyograph (EMG) for muscle activity and has an acceleration pattern which approximates a sinusoidal waveform. When the Index of Difficulty for such a movement is less than 3.0, the movement time is found to be related to the square root of the movement amplitude. The occurrence of ballistic movement is determined by the combined factors of Fitts' Index of Difficulty and movement amplitude.
A mathematical model is developed for ballistic arm movements in an underwater environment. Characteristics of the arm moving in water, the 'induced' moment of inertia and drag coefficient, are found from experiments on an artificial arm. These data, along with the mathematical model, are used to predict underwater movement times from experimental data for movement times in air.Experiments on two groups of subjects, in both air and water environments, show that the model yields a good prediction of ballistic movement times in an underwater environment.
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