BASEBALL BAT SCIENCE: Baseball bats are traditionally made from wood. Bats used in amateur baseball are almost always metal or even composite. Wood bats do not deform much when striking the ball, but the ball itself does, squishing up and then rebounding off the bat. When the ball hits a hollow bat (metal or composite), it does not deform very much, but the bat does. The bat then rebounds like a spring and returns that lost energy back to the ball, which is called the trampoline effect. Hollow bats are also designed to have a larger sweet spot on the barrel, meaning that a larger portion of the bat is able to impart the greatest amount of energy from the swing into the flight of the ball.
SWINGING A BAT: The most efficient way to swing a bat starts with the large muscles in the lower body, like the thighs in hips. The rotational energy of those muscles is transferred upward and to smaller muscles until it is transferred to the arms, to the hands, and on to the bat.
SCIENCE OF THROWING HARD: Being the strongest baseball player does not necessarily make it easier to throw harder. In order to throw the ball hard, the pitcher must use his strength efficiently, which can be accomplished by throwing with a proper motion. Conveniently, this same motion allows pitchers to maximize the speed at which they throw, and minimizes their chance of injury, because it imparts the least stress on the elbow and shoulder.