Forces play a major role in sprinting. Forces acting during the race are actually more important than how fast the limbs are moving when trying to achieve higher speeds.

Forces Acted on the Runner:

Propulsion- This is the force applied by the muscles for a forward motion causing acceleration

Wind- This is the force applied on the runner by the wind which can cause acceleration or deceleration depending on its direction.

Drag- This is the force of air resistance which causes deceleration.


GROUND REACTION FORCE

The Ground Reaction force is a reaction force. It is produced when the sprinters foot interacts with the track while some or all of the body is accelerating.

Law of Action-Reaction: this law states that for every applied force there is an equal and opposite force. Therefore the ground reaction force is the opposite of the force produced by the runner's foot interacting with the track. The Ground Reaction force represents the reaction of the track to the acceleration of the center of mass of the sprinter.

the GRF acting on the foot

Frictional force: This force is the force that acts parallel to the runner in the opposite direction. It depends on how the track and the runner's foot interact and the normal force (force acting perpendicular to the surface which the ground exerts) between them.


As sprinting has developed over the years, runners have learned how to use some of these forces to their advantage. One of them being the force of GRAVITY.

The force of gravity is the force exerted between two masses of different sizes. The smaller mass is attracted to the larger. In our case the world is the large mass, and we are the smaller masses. The force of gravity pulls us towards the earth and that's why we do not float off into outerspace.

Runners can use gravity do their advantage. In order to use gravity to work with them, runners lean forward. Leaning allows gravity to pull the runner forward, and it makes the work done by the legs easier. If the runner developes the proper lean(from the ankles, not the waist) he or she will be able to run easier and faster. The force of gravity will allow this.

this shows the lean a runner must have run easier