When playing any sport there is a lot of impact on the players bodies which can cause them to get hurt. During a hockey game you seem more checks than you can count but if hockey players knew what to do when they were about to get hit the number of injuries would reduce immensly. If a really big guy is coming at you, he's going to have a really big momentum when he hits you and that momentum will turn into impulse on you as soon as he hits you. To reduce this, considering you can't reduce how much force the player hits you with, you should relax. When you relax your body has more time to absorb the hit and in turn will result in less direct impact on the player and in turn will result in less injuries. This works the saem way an airbag does. An object in motion will remain in motion unless acted upon by an outside force and if you are stiff you are going to absorb all of the person who's checking yous force. If you relax and don't tense up then your body will have more time to slow down the person checking you. This will help reduce injuries in sports because if people know to relax the shock will absorbed over a longer period of time versus all at once.