According to research published in the February Journal of Strength and Conditioning Research, Swinging a weighted bat before hitting doesn’t enable a baseball hitter to swing any faster.
Scientists at three universities asked 22 collegiate baseball players to take three swings each with a test bat, followed by two easy swings with each player’s game bat, unweighted. Each player then hit three balls off a tee. The tests bats included six bats variously weighted, two normal bats without weights and two underweight bats.
The experiment was repeated by the players daily for 10 days.
None of the test bats affected bat speed substantially.
The swings ranged from 87.7 to 89.2 miles per hour off the tee.