An Exploratory Study of Arm-Reach Dynamics Under Several Levels of Gravity

Four adult male subjects made vertical reaching movements, upward and downward, over 10, 20, and 30 in. distances; these movements were performed under weightlessness (0-0g), Martian gravity (0-38g), Earth gravity (l-0g), and 1-3G. The movements were recorded with a movie camera running at 64 frames per second. The subject's arm was considered as consisting of two rigid parts: the upper arm and the lower arm. Three instantaneous velocities over the entire movement were derived from the film records to describe the motion of these parts: the linear velocities of the centres of mass in both the horizontal and vertical directions, and the angular velocity of each part. Reach times, both maximum angular velocities and maximum lower arm velocity were selected as criterion measures. They were found to be affected by reach distance, reach direction, and gravity level (in descending order of importance). The need to study accelerations, force or torque reactions, and energy expenditures during movements is indicated.