Skilled throwers use physics to time ball release to the nearest millisecond.

Skilled throwers achieve accuracy in overarm throwing by releasing the ball on the handpath with a timing precision as low as 1 ms. It is generally believed that this remarkable ability results from a precisely timed command from the brain that opens the fingers. Alternatively, precise timing of ball release could result from a backforce from the ball that pushes the fingers open.

Deliberate utilization of interaction torques brakes elbow extension in a fast throwing motion.

We tested the hypothesis that in fast arm movements the CNS deliberately utilizes interaction torques to decelerate (brake) joint rotations. Twelve subjects performed fast 2-D overarm throws in which large elbow extension velocities occurred. Joint motions were computed from recordings made with search coils; joint torques were calculated using inverse dynamics.

Wrist muscle activation, interaction torque and mechanical properties in unskilled throws of different speeds.

An unexpected property of unskilled overarm throws is that wrist flexion velocity at ball release does not increase in throws of increasing speed. We investigated the nature of the interaction torques and wrist mechanical properties that have been proposed to produce this property. Twelve recreational throwers made seated 2-D throws, which were used as a model for unskilled throwing.

A novel shoulder-elbow mechanism for increasing speed in a multijoint arm movement.

The speed of arm movements is normally increased by increasing agonist muscle activity, but in overarm throwing, an additional effect on speed may come from exploitation of interaction torques (a passive torque associated with motion at adjacent joints). We investigated how the central nervous system (CNS) controls interaction torques at the shoulder and elbow to increase speed in 2-D overarm throwing. Twelve experienced throwers made slow, medium, and fast 2-D throws in a parasagittal plane.

Kinematics of arm joint rotations in cerebellar and unskilled subjects associated with the inability to throw fast.

Cerebellar subjects and unskilled throwers cannot produce fast arm movements when throwing. We investigated the arm movement kinematics associated with this lack of skill. Cerebellar subjects and matched controls, and skilled throwers throwing with their skilled (dominant) and unskilled (nondominant) arms, were instructed to make slow, medium, and fast 3-D overarm throws from a sitting position.

Comparison of kinematics in skilled and unskilled arms of the same recreational baseball players.

We examined mechanisms of coordination that enable skilled recreational baseball players to make fast overarm throws with their skilled arm and which are absent or rudimentary in their unskilled arm. Arm segment angular kinematics in three dimensions at 1000 Hz were recorded with the search-coil technique from the arms of eight individuals who on one occasion threw with their skilled right arm and on another with their unskilled left arm. Compared with their unskilled arm, the skilled arm had: a larger angular deceleration of the upper arm in space in the forward horizontal direction; a larger shoulder internal rotation velocity at ball release (unskilled arms had a negative velocity); a period of elbow extension deceleration before ball release; and an increase in wrist velocity with an increase in ball speed.

Timing of ball release in overarm throws affects ball speed in unskilled but not skilled individuals.

We tested the hypothesis that variability in the timing of ball release in overarm throws affects ball speed. Nine unskilled and six skilled throwers made 30 throws fast and accurately from a sitting and standing position. Angular positions of finger and arm segments were recorded with search-coils at 1000 Hz; ball speed was measured with a radar gun.

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.

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.

Braking of elbow extension in fast overarm throws made by skilled and unskilled subjects.

A previous computer simulation study of overarm throws in 2D showed that reversal of elbow torque by antagonist muscle action late in the throw led to increased wrist flexion velocity and to increased ball speeds. We tested the hypothesis that the skill of making fast overarm throws in 3D involves deceleration (braking) of elbow extension before ball release, and that this is an active mechanism. Skilled and unskilled throwers were instructed to throw baseballs at a fast speed.

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.

Kinematics of wrist joint flexion in overarm throws made by skilled subjects.

Previous studies of multijoint arm movements have shown that the CNS holds arm kinematics constant in different situations by predictively compensating for the effects of interaction torques. We determined whether this was also the case for wrist joint flexion in natural overarm throws performed by skilled subjects in 3D, a situation where large passive torques can occur at the wrist. Specifically, we investigated whether wrist flexion amplitudes are held constant in throws of different speeds.

Overarm throwing speed in cerebellar subjects: effect of timing of ball release.

Cerebellar subjects cannot throw fast and show variability in ball speed from throw to throw. One possible reason is that they release the ball at times when arm speed is not at its maximal value. Therefore, we investigated the hypothesis that the slow and variable speeds of throws made by cerebellar subjects are caused by their known large variability in the timing of ball release.

Disorders in timing and force of finger opening in overarm throws made by cerebellar subjects.

Although there is agreement that an important sign of cerebellar dysfunction is disorder in timing of movement, it appears that authors who study different behaviors mean different things when they use the term "timing," and that the underlying mechanisms are likely to be different. For overarm throwing, skilled throwers can time ball release with a precision of less than 7 ms, whereas cerebellar subjects show a large variability of 50 ms or more in this timing. Furthermore, cerebellar patients show a larger variability in the amplitude of finger opening which could either reflect a disorder in force, or result indirectly from the increased variability in timing.

Increased variability in finger position occurs throughout overarm throws made by cerebellar and unskilled subjects.

We investigated the ability of cerebellar patients and unskilled subjects to control finger grip position and the amplitude of finger opening during a multijoint overarm throw. This situation is of interest because the appropriate finger control requires predicting the magnitude of back forces from the ball on the finger throughout the throw and generating the appropriate level and rate of change of finger flexor torque to oppose the back force. Cerebellar patients, matched controls, and unskilled subjects threw tennis balls and tennis-sized balls of different weights.

Control of finger grip forces in overarm throws made by skilled throwers.

In an overarm throw, as the hand opens and the ball rolls along the fingers, the ball exerts a back force on the fingers. Previous studies suggested that skilled throwers compensate for this back force by producing an appropriate finger flexor torque to oppose the back force, but it was unclear how this is controlled by the CNS. We investigated whether the increase in finger flexor torque is timed precisely to occur late in the throw as the fingers open or whether the increase occurs throughout the throw to anticipate the increase in hand acceleration.

Causes of left-right ball inaccuracy in overarm throws made by cerebellar patients.

Cerebellar patients throw inaccurately in the left-right direction but the cause of this multijoint ataxia is unclear. We tested whether it was due, as originally proposed, to variable left-right directions of the hand path, or, alternatively, to variable timing of ball release occurring on a right to left curved hand path. We also examined the cause of the variability in hand path direction per se.

Prediction and compensation by an internal model for back forces during finger opening in an overarm throw.

Previous studies have indicated that timing of finger opening in an overarm throw is likely controlled centrally, possibly by means of an internal model of hand trajectory. The present objective was to extend the study of throwing to an examination of the dynamics of finger opening. Throwing a heavy ball and throwing a light ball presumably require different neural commands, because the weight of the ball affects the mechanics of the arm, and particularly, the mechanics of the finger.

Failure of cerebellar patients to time finger opening precisely causes ball high-low inaccuracy in overarm throws.

We investigated the idea that the cerebellum is required for precise timing of fast skilled arm movements by studying one situation where timing precision is required, namely finger opening in overarm throwing. Specifically, we tested the hypothesis that in overarm throws made by cerebellar patients, ball high-low inaccuracy is due to disordered timing of finger opening. Six cerebellar patients and six matched control subjects were instructed to throw tennis balls at three different speeds from a seated position while angular positions in three dimensions of five arm segments were recorded at 1,000 Hz with the search-coil technique.

Finger opening in an overarm throw is not triggered by proprioceptive feedback from elbow extension or wrist flexion.

Accuracy in an overarm throw requires great precision in the timing of finger opening. We tested the hypothesis that finger opening in an overarm throw is triggered by proprioceptive feedback from elbow extension or wrist flexion. The hypothesis was tested in two ways: first, by unexpectedly perturbing elbow extension or slowing wrist flexion and determining whether changes occurred in finger opening, and second, by measuring the latency from the start of these joint rotations to the start of finger opening.

Overarm throws with the nondominant arm: kinematics of accuracy.

1. Overarm throws made with the nondominant arm are usually less accurate than those made with the dominant arm. The objective was to determine the errors in the joint rotations associated with this inaccuracy, and thereby to gain insight into the neural mechanisms that contribute to skill in overarm throwing.

Finger flexion does not contribute to ball speed in overarm throws.

The aim of this study was to determine whether, in overarm throws made by recreational ball players, the fingers undergo flexion movement before ball release and thereby contribute to the generation of ball speed. To obtain the high resolution needed to answer this question, the magnetic-field search-coil technique was used and the data were sampled at 1000 Hz. The subjects, who were either seated or were standing, threw tennis balls at different speeds at a target 3 m away.

Motor control, excitement, and overarm throwing.

Although motor control has historically been an important discipline, it runs the risk of being overshadowed by other newer areas of neuroscience. One response would be to generate increased excitement in motor control, e.g.

Errors in the control of joint rotations associated with inaccuracies in overarm throws.

1. Accurate overarm throwing requires precise control of joint rotations so that the ball is released at the appropriate time on the appropriate hand trajectory. Inaccuracy in throws, in turn, must result from errors in the control of joint rotations.

Timing of finger opening and ball release in fast and accurate overarm throws.

How precisely does the CNS control the timing of finger muscle contractions in skilled movements? For overarm throwing, it has been calculated that a ball release window of less than 1 ms is needed for accuracy in long throws. The objective was to investigate the timing precision of ball release and finge opening for 100 overarm throws made using only the arm. Subjects sat with a fixed trunk and threw balls fast and accurately at a 6-cm-square target when it was 1.