Call it mind over physiology, a belief in the practices that have brought them to this level, but hitters are just now digesting the news that their time-honored on-deck routines are wrong. Scientific research makes clear that the more weight you swing in the on-deck circle, the slower your swing in the batter’s box. The slower the swing, the harder it is to catch up to searing fastballs and do what’s considered the toughest task in sports: get a base hit.

Coop DeRenne, a physical-education professor at the University of Hawaii, frames his findings in hard numbers: Increase—or even decrease—the weight of your bat between 10% and 13%, and you decrease bat speed from three to five miles per hour.

“As much as possible,” says DeRenne, who is known as the guru of the on-deck ritual among those who study the science of hitting, “the batter should mimic in his warm-up what he will do in the game—the same weight, the same motion.”