Newton's third law of motion

science
action force: Tires push back on road.
reaction force: road pushes forward on tires.
In this example you see a skateboarder, you see as his weight on the skateboard is being exerted onto the ground, the ground is also exerting an equal force onto the skateboard

Newton’s third law discusses action and reaction forces, whenever one object  
exerts a force on a second object, the second objects exerts an equal  
and opposite force on the first object. 
  If you push horizontally against a wall with a force, then the wall  
will push horizontally against the person with  
the same amount of force. No matter what the mass or weight is, the forces will be equal upon eachother.

action force: Man pushes forward on wall.
reaction force: wall pushes backward on man.
 
As the pictured here, the runner exerts his force as he runs along the path, but at the same time it might not seem like it but the path is actually pushing the same equal force upon the runner as well.