Biomedical subjects

Jon Hore

Publications and source records attributed to Jon Hore.

3 recordsLinked to original sources

PubMed2005

Control of joint rotations in overarm throws of different speeds made by dominant and nondominant arms.

We tested the hypothesis that dominant and nondominant overarm throws of different speeds are made by time-scaling of joint rotations, i.e., by joint rotations that have the same positions and amplitudes but that are scaled in time. Eight skilled subjects stood and made overarm throws with both their dominant and nondominant arms. Six joint rotations were computed from recordings of arm segments made with the search-coil technique. Throws made with nondominant arms were less accurate and had lower ball speeds. In contrast to the hypothesis, dominant arms showed large and consistent differences between fast and slow throws in six-dimensional angular position joint space. These same throws showed similar hand angular paths when these were time-scaled based on ball speed. Nondominant arms showed only small differences in angular position joint space in fast and slow throws. It is concluded that a joint space pattern resembling that predicted by time-scaling occurs in nondominant arm throwing when it is unskilled. However, time-scaling does not occur in dominant arm throwing, i.e., a skilled fast throw is not simply a skilled slow throw whose joint positions and amplitudes remain constant but whose joint velocities are sped-up. We hypothesize for future study that, when subjects first learn to throw at different speeds with their dominant arms, they use time-scaling of joint rotations that involves compensating for interaction torques; then as they become skilled at throwing fast, time-scaling is superseded by a more complex pattern of interjoint coordination that involves exploiting interaction torques.

Adult↗

PubMed2005

Timing finger opening in overarm throwing based on a spatial representation of hand path.

Previous studies on overarm throwing have suggested that throwing accuracy depends on a precise central timing mechanism. In the present study, we investigated an alternative hypothesis: that central control of finger opening is based on an internal positional representation of handpath. Angular positions of each segment of the middle finger, thumb, and arm were recorded with the search-coil technique as subjects made slow, medium, and fast throws at a target 3.1 m away. Onset of ball release from the hand was strongly correlated with extension at the proximal interphalangeal joint (PIJ). The velocity of this finger joint opening varied with the speed of the throw. In agreement with the hypothesis, at a fixed hand angular position in space, there was no difference across subjects in the amplitude of extension at the PIJ for throws of different speeds. That is, for these two parameters, a fast throw was the same as a slow throw that was sped-up. This occurred irrespective of whether the trunk was constrained (sitting throws) or unconstrained (standing throws). No equivalent relation was found between extension at the PIJ and elbow extension. These findings support the idea that precisely timed finger opening in overarm throwing depends, not on a central timing controller that triggers a step-like (ballistic) finger opening at the right moment in throws of different speeds, but on a central spatial controller that matches angular positions of finger opening to the intended handpath.

Adult↗

PubMed2004

A simple rule for controlling overarm throws to different targets.

We investigated the central programming of overarm throws by determining whether throws to spatially separate targets in the vertical direction (sagittal plane) are produced by changes in hand (i.e., finger) path direction or by changes in the timing of ball release. Six skilled throwers made 30 throws at the same speed with a baseball, from a sitting position with the chest fixed, at targets at different heights and distances. Arm segment angular positions in 3D were recorded with the search-coil technique. Videotaping revealed that ball direction was not, as commonly assumed, the tangent to the finger path at ball release. Rather ball direction was the tangent to the finger path at a point about half way between initial uncoupling of the ball from the hand and final ball release. When viewed from the side, finger paths were tilted upwards for the high and the far targets and downwards for the low and near targets. This was associated with changes in angular orientation of the upper arm in space. Throwing at spatially different targets was not associated with changes in the timing of ball release. We propose that there is a simple rule by which throws to targets in different directions and at different distances are controlled: throws of the same speed are produced by different finger path directions, but the same timing of ball release. Such a mechanism would simplify the neural control of throwing to different targets.

Analysis of Variance↗