A helmet must generally deform to disperse energy, just way the bike version breaks after a crash. Disposable helmets are also inconvenient for football players. When a bike helmet breaks, it absorbs what is known as "impulse," which is a subsequent result of an initial force. For example, if a player falls off his bike and hits the ground, there would be no impulse because there was no first cause for the deformation of the bike helmet. Helmets for other sports such as hockey and lacrosse also need to deform in order to reduce the severity of injuries that may occur during play. In fact, most major sports utilize some type of protective gear for their athletes. Football is no exception with players wearing helmets that must deform in order to protect them from injury. The amount of energy that needs to be absorbed by a football helmet depends on how hard the player impacts the ground. If the player contacts the ground at a low velocity, then he or she will not suffer a severe injury. However, if the player contacts the ground at a high velocity, then more energy needs to be absorbed by the helmet in order to prevent serious damage. Helmets that do not absorb enough energy will allow the player to suffer serious injury after only a few collisions with the ground. Helmets that absorb too much energy will cause them to break down before the end of the season.