## Generating Power in Execution of Sports Skills

Part I

The formula for force, F = mxa, is, fairly well-known among athletes and coaches. What is not always understood is exactly how this formula functions in the execution of different skills. For example, you can generate force through weight transference (shift), summation of bodily forces and in a pushing action. Each of these methods involves different technique and sometimes all three can be combined into a single skill execution, as for example, in the shot­put or throwing a baseball. You can generate force through weight transference (shift), summation of bodily forces and in a pushing action.

Hip Abduction with Hip Rotation

In this case, begin with the hip abduction in shifting the hips forward onto the forward leg, and at that time rotate the hips toward the target. However, as you do this the shoulders must still remain back in a side facing position.

It is important to learn to isolate this movement. In most sports, if power is the key there should always be a separation between the movements. Thus, in this exercise you learn not only weight shift, but also the next move which is usually hip rotation.

Before looking at these separate factors it is first important to understand that only the muscles can generate force. They create the force by which the bone is placed into motion which can then be accelerated. Note also that it is acceleration that is needed in the production of force. When force is being applied the object is accelerated so that it moves faster than previously.

This means that there must be a change in speed or velocity of the moving implement. Merely maintaining a constant speed of movement of a bat or other implement does not mean generation of force. It only signifies that you have momentum, i.e., the implement is moving on its own accord or at a steady speed.

When force is being applied the object is accelerated so that it moves faster than previously. (Note that in the follow through, the movements are successively slower, an example of negative acceleration). Thus a multitude of sports skills that involve production of force will in essence be ballistic because of the acceleration factor.

In events like powerlifting or bodybuilding there is initial production of force to get the barbell or dumbbell moving. But once it is in motion it moves at a constant rate of speed. As a result, there is no longer production of additional force. Note that other factors are also involved such as angle of muscle insertion, mechanical advantage, etc., that also play a role in speed of movement.

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Since the muscles are the key to the production of force, must look at which muscles are most important and how they contract. The key is to know which actions produce the movements that create acceleration and the force needed to propel an object with speed and accuracy.

Weight shift is a very precise movement that can contribute up to 20% of the total force generated in a particular skill.

Weight Shift

Weight shift is often taken for granted, but it is a very precise movement that can contribute up to 20% of the total force generated a particular skill. The maximum contribution comes from a run up prior to the execution of the total skill, as for example, in the javelin throw. Baseball players utilize the run up to develop more speed on the ball to when throwing to the infield or to home plate.

In many sports skills such as hitting a baseball or tennis, ground strikes only a slight step (stride) forward is used to accomplish weight shift. In the golf swing, the feet remain stationary so that the weight shift takes place with movement of the hips. This action is also used in the tennis serve or when hitting or throwing easy.

Which muscle action is most important in these weight shifts? In the stridíng (stepping) action the key action is hip joint abduction, i.e., the muscles on the sides of the hip, the gluteus minímus and medius contract to push the pelvis forward. Since the weight is moving forward you are forced to step out to maintain balance.

By stepping out and moving the pelvis (or trunk) forward you are in essence shifting the weight. Note that the pelvis is typically where the center of gravity (CG) is located, and once we place the CG (or center of mass) of the body in motion it can be said that the body is now in motion.

When you step out, the step must be preceded by hip joint abduction. Thus, we have the beginning of the production of force with this seemingly simple action. You should also understand that when you step out, the step must be preceded by hip joint abduction. If this

action did not occur it would be impossible for you to step out. Note also that when you step out, the action is hip abduction of the forward leg.

Fitness and Sports Review International, 28-5&6, 1993

Positioning

The hip abduction is the key action when you are in a side facing position. Therefore, if initially you are in a forward facing position, you must turn sideways into the throwing or hitting stance. Then you can use hip abduction to shift the weight and to step out. 'I'his action sets you up for the following hip and shoulder rotation. These actions are needed to generate additional force in the throw or hit.

The weight shift is important for setting up a new axis of rotation in the front leg which increases the power (force) arm when you have hip and shoulder rotation. This in turn creates even greater force. Also, without this preliminary weight shift, it is virtually impossible to throw or hit with force or to even have a smooth swing or throw.

In many sports such as golf, weight shift is executed while maintaining the feet in contact with the ground. In this case, you must execute hip abduction so that the hips move forward without stepping forward. I strongly recommend that you master weight shift in this manner. When you can do it with the feet stationary, you will be able to incorporate it after a run up or stepping forward. In this case, the hip abduction occurs to imitate the summation of forces.

The weight shift is important for setting up a new axis of rotation in the front leg which increases the power (force) arm when you have hip and shoulder rotation.

In golf, as well as in the tennis serve, weight shift is needed to establish a new axis of rotation on the left side as well as getting additional force from the movement. When the hips come through first in the weight shift, and then rotation, it enables the shoulder rotation and the following arm actions to occur without danger to the spine.

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A simple progression that can be used for learning weight shift is to first start off standing with your feet spread slightly wider than shoulder width apart. Execute hip abduction on the rear leg and shift the hips only onto the left leg. Keep the head and shoulders in place. Practice doing this until it becomes easy. After mastering this movement, go to the hip abduction with a step.

When the hips come through first in the weight shift, and then rotation, it enables the shoulder rotation and the following arm actions to occur without danger to the spine.

Exaggerated movements are needed for learning purposes. An exaggerated movement helps to emphasize the action and is easier than trying to do it only as needed in the competitive sport. Also, it is much easier to cut down the range of motion at a later date than it is to increase it at a later time.

The exaggerated movements set up a strong visual picture for the athletes to see and try to imitate. Thus, learning weight shift should be the very first movements that an athlete learns in the throwing and hitting sports. Once these movements are mastered then they can move on to developing a summation of forces which involves the other major joints. It will be covered in the next issue.