The cushioning of running shoes varies from trainers to racing shoes.
Trainers are used in racking up mileage by the runner to help them improve their bodies for the races. This is where the cushioning of the shoes comes into play and is very important as it helps relieve stress applied to the feet of the runner.
The foot strike of the runner can range from the back of the foot to middle to the forefoot and the normal force to the shoe is known as the impact force. Whatever the case may be the cushioning of the shoe lies in the back and front of the shoe where it’s needed since those are the areas where most of the impact force is applied to according to the figure (Cavanagh & LaFortune, 1980) which shows the pressure according to runners that strike the ground from the heel area, the middle, and the forefoot.
& LaFortune, Strike Index, 1980,
Cushioning works by increasing the amount of time the force is applied. A small force applied for a long time can produce the same momentum change as a large force applied briefly.
I = F∆t
J is impulse
F is the force, and
is change in the amount