Sports are all about form too. For throwing something, if you have good form that object could go further or straighter versus if you had bad form. If you were running with bad form, you would be slower and have worse endurance than if you were running with your head held high and your arms pumping. Good form could also help prevent soreness.
Now, I know it could use up more of your energy when you remind yourself to keep your form. It's tiring. I know. But once you get into the habit of keeping that form, you would improve greatly.
For sprints, you should keep yourself straight, and the only things that aren't straight are your legs, which should be bent at 90 degrees max. Your arms should be chopping the air as fast as possible. They are just as important as your legs. The faster your arms move, the faster your legs go, so MOVE THOSE ARMS!
For long distance running, you should also mind your arms. Lean forwards a little bit to kind of "catch yourself" while running. Also, you should keep your strides long and "glide" over the ground. This would improve your speed, and it would use less energy. Your feet should not be making much noise on the ground. Don't make your movements jerky - make smooth motions and be "one well oiled machine". Distance running is harder on your knees, ankles, and hips than most sports, so to help prevent great impacts, land on your heels, then roll onto the balls of your feet, then to your toes and push off.
For throwing, you should wind up a teeny bit, but don't "fight yourself". Don't put your arm directly behind your head. That makes it more difficult to throw. You should give it your all when you throw, and kind of turn into the throw.
For jumping (to spike or shoot, etc.), you should start in a partial squat position, tense your muscles, then jump straight up. Don't kick your legs back, like most people do. It's dangerous (it increases your chances of falling and injuring yourself) to do so, and it uses more energy. When you land, land on your tippy toes, then on the balls of your feet, then roll down to your heels. This prevents a jarring impact which is bad on your knees, ankles, and hips, like in running distance.
If you're batting in baseball, softball, etc., sorry, but I can't help you. I know how to hit the ball and run, the strikes, outs, fouls, and such, but that's about it. I know nothing about form in baseball.
And there you go! Now keep your posture, person reading this blog!
If there are any sports that you want to improve your form on, but don't know how, please comment!