Biomechanics

Linear momentum is the product of mass and velocity and implies a quantity of motion in a straight line.

The relationship is expressed as M = mv (momentum = mass x velocity)

Momentum is one of the most important concepts in biomechanics and is used frequently in sport biomechanics to describe and explain collisions and the generation of speed in throwing and striking actions. The larger the mass of an object the greater its momentum will be.

In activities such as the javelin throw, shot put, and discus, maximum momentum is needed. Effort is required from the whole body, and the momentum of different parts of the body are summed to achieve the highest possible hand velocity.

Stabilisation is a necessary element in all throwing skills. As well as being necessary for maximising the momentum of the object being thrown or struck, stabilisation serves to hold the different parts of the body accurately in position.

Stabilisation occurs by: Lowering the Centre of Gravity Widening the base of support

When the body is stabilised, the total momentum in a throwing action is the sum of the individual momentum of different body parts. Generating high momentum is of critical importance in developing maximum distance in the throw.

Generating Momentum can be achieve by:1. Use of Body Segments2. Optimum Stretch3. Sequence of movement of body segments4. Optimum contribution of body movement5. Range of motion

To generate maximum momentum in an object being thrown, use as many body segments as possible in the throwing action.

For example, in a javelin throw, the body segments contribute to the action in the following sequence: legs, hips, spine, shoulder, upper arm, forearm and wrist.

Before the sequence of movements of the body segments in throwing action, the muscles involved should be stretched to optimal lengths.

For example: In discus:

To generate maximum momentum in throwing and jumping movements, the small body segments that are capable of moving fast, e.g. The arms and hands, must be used last in the sequence.

However, the larger, slower segments that move earlier in the sequence e.g. the hips, play an important role in generating momentum.

In a throwing or jumping action, it is important that each body segment makes an optimum contribution at exactly the right time before the next body part begins to move.

For example in discus

To achieve the maximum speed in the object being thrown or hit, the body segments must track over the greatest possible range of movement.

For example, the more body segments that contribute to throwing a discus, the greater the range of motion of the last segment – the arm and finger release of the discus. The greater the range of motion of body during the preparation phase, higher the speed will be when the hand releases the discus.

Using a tennis ball, perform the following activities with a partner, one person throwing and one marking.

Condition A: Take up a long sitting position against a wall. Keep the shoulders and hip tight against the wall. The task is to throw a tennis ball with maximum effort over the greatest possible distance. Keep the angle of release consistent.

Condition B: Move 1m away from the wall, but remain in along sitting position. Rotate the shoulders and arm back as far as possible to make the throw but keep the body upright, not leaning back. Throw the ball using shoulders and arm only.

Condition C: Move 2m away from the ball and stand square to the direction of the throw. Rotate the hips and shoulders as far back as possible to make the throw. The feet must remain in contact with the ground and must not twist around. Throw the ball using the hips, shoulders and arms only.

Condition D: Stand side on to the direction of the throw, with feet shoulder width apart and back knee straight. To make the throw, rotate the trunk as far back as comfortable. Throw the ball using the hips, shoulders and arm. The feet should remain in contact with the floor.

Condition E: Repeat condition D, but now step forward and throw the ball.

Do the results show a progressive increase or decrease in distance of the throw?

List the body parts used in the throw made under each set of conditions.

List the order in which these body parts should be used in a correct throwing sequence.

Using the principle of momentum summation, what general observations can be made regarding the mass of the body parts used in the throwing sequence?

Explain why the side-on position (used in conditions D and E) permits the production of greater force in the throw.

Which concept in momentum summation underlies this explanation?