A baseball doughnut is a weighted ring that fits over the end of a baseball bat, used for warming up during a baseball game. A doughnut can help increase bat speed. Doughnuts can weigh as little as 4 oz. and as much as 28 oz. Players feel baseball doughnuts increase bat velocity because after warming-up with a baseball doughnut then decreasing the weight after taking the doughnut off, the swing feels faster.[1] The heavier load of the weighted bat stimulates the neural system and increases muscle activation during lighter bat swings. Researchers have found that muscle contractions are stronger after reaching near maximal loads. One research study also found that additional weight added to the bat may strengthen the muscles of the forearms and wrists.[2] Baseball doughnuts are based on the theory of complex training, which alternates the use of heavier and lighter weights to increase explosive power. By increasing the number of motor units recruited this training increases muscle performance.

The doughnut was created by former New York Yankees catcher Elston Howard. Howard, in 1955, was the first African-American player on the Yankees’ roster. He played catcher and the outfield during his time with the Yankees. The first team to invest in Howard’s product was the St. Louis Cardinals. This essentially got players out of the habit of swinging multiple bats to warm up.[1] While Howard is credited with inventing the doughnut, he did not make the amount of money he had hoped due to other companies making their own versions of the batting doughnut. Howard and his supporters did not have the funds to take the companies to court.[1] During a game, you can find the doughnut lying in the on-deck circle. The player in the on-deck circle normally swings a bat and stretches to prepare for his at-bat. The different doughnuts weigh varying amounts. The doughnut is discarded in the on-deck circle when the player moves into the batter’s box.[1] The weight was later dubbed the “doughnut” and the “iron doughnut”.[3]

Reference: http://en.wikipedia.org/wiki/Bat_weight