In a set of three experiments, we show that after an auditory "go" signal, subjects simultaneously initiate and terminate two-handed movements to targets of widely disparate difficulty. This is the case when the movements required are (a) lateral and away from the midline of the body (Experiment 1), (b) toward the midline of the body (Experiment 2), and (c) in the forward direction away from the body midline (Experiment 3). Kinematic data obtained from high-speed cinematography (200 frames/sec) point to a tight coordinative coupling between the two hands. Although the hands move at entirely different speeds to different points in space, times to peak velocity and acceleration are almost perfectly synchronous. We believe that the brain produces simultaneity of action as the optimal solution for the two-handed task by organizing functional groupings of muscles (coordinative structures) that are constrained to act as a single unit.

The purpose of this study was to determine if warm-up with baseball bats of different moments of inertia has an effect on swing pattern and bat velocity. Ten experienced baseball players (ages 20-25 years) voluntarily participated in this study. Each participant was required to complete 10 dry swings (5 warm-up and 5 postwarm-up) at maximum effort within 3 different conditions. Post warm-up was always with a standard bat (I = .27 kgm2; 83.8 cm, 9.1 N). Warm-up for Condition 1 was with the standard bat. Condition 2 required participants to warm up with a standard bat plus a 6.1 N lead donut (I = .49 kgm2, 83.8 cm, 15.6 N). Condition 3 required participants to warm up with a hollow plastic bat (I = .08 kgm2; 83.8 cm, 3.34 N). Quantitative and qualitative analyses indicated that following warm-up with the weighted bat (largest moment of inertia), swing pattern was significantly altered, and post warm-up velocity was the lowest of the three conditions.

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The purpose of this study was to determine if change in segmental mass and increases in throwing velocity act as control parameters to alter throwing patterns. Twenty participants were categorized into four levels of throwing pattern. Each participant was required to make 10 throws at various velocities within 8 conditions. Conditions resulted from combinations of altered mass of the arm, forearm, and hand. Quantitative and qualitative analyses indicated that changes in segmental mass and release velocity either increased or decreased levels of throwing pattern depending on the initial throwing level. It was concluded that mass and velocity may be control parameters which instigate changes in throwing patterns.

The purpose of this study was to determine the importance of timing during an auto-communicative ritual to successful performance. Eight members of a university varsity basketball team served as subjects for this study. Each subject performed 15 free throws in each of four different conditions. Condition 1 required subjects to use their standard free throw ritual prior to shooting. Condition 2 required subjects to maintain the relative timing of ritual behaviors but reduce the absolute time of the ritual by one-half. Condition 3 required that relative timing be maintained but that the absolute time of the ritual be doubled. Condition 4 required the same behaviors and the same absolute time as the standard ritual but that the relative time of the ritual be altered. Data were collected with a 16-mm high-speed camera. Types of behaviors, timing aspects of the ritual, successful attempts, and shot mechanics were dependent measures. Analysis of variance (ANOVA) of dependent measures and Fisher's scores from correlation coefficients of dependent measures indicate that relative timing of behaviors (rhythmicity) is more important to success than the absolute time of rituals. Behaviors most important to free throw success are those that may be totally controlled by the subject and yet remain stable with changing conditions.