Doughnut or Doughnot, there is no try...
For years, baseball players have been using bat weights to improve their swing speed–does it work?
In the on-deck circle, before an at-bat in a baseball game, there are a lot of thoughts flying through the average player’s mind: ‘I’m feeling stiff today,’ ‘that pitcher is throwing pretty hard,’ ‘how many outs are there?’ More visibly, you will often see a weight on the end of their bat, called a doughnut. Many hitters use this because it makes the bat feel heavier to swing while it’s on – and the opposite when you take it off. In other words, your bat feels lighter after swinging with a doughnut, which would normally translate to a faster swing speed, and thus a better chance at hitting the ball. But is this just a feeling, or a real, concrete phenomenon?
To understand how important bat lightness is, you need to consider the fractions of a second that a hitter has to react to a thrown pitch – a mere 400-500 milliseconds from the release of the ball to the ball crossing the plate! Even more, due to limits on human reaction time, the act of swinging itself only has 150-200 milliseconds to occur. Naturally, hitters want all the advantages that they can get especially when it comes to timing and having a ‘fast bat.’
So, how does a doughnut affect a player’s swing? Now for the psychics. The first thing to understand is the function of the doughnut – what it changes about the bat. When adding a doughnut to a bat, it might appear that you are simply making the bat heavier (you are), but in addition what you are actually doing is changing the inertia of the bat. The inertia is, in plain terms, how hard it is to get something moving; the higher the inertia, the harder an object is to move. In the case of a baseball swing, much of the inertia is called rotational inertia, as the bat rotates around the player. Roughly, rotational inertia for a rod at its end (in this case, the bat) is defined as ⅓ML2 where M is mass and L is length. When you add a doughnut to the end of the bat, you are 1) increasing the mass and 2) moving the center of mass further down the bat, thereby increasing the length. Both of these combine to increase the inertia. So, adding a doughnut does more than simply make the bat heavier.
This brings us back to the main question of whether adding a doughnut increase a player’s bat speed. There have been a multitude of studies examining this question and the answer is rather clear – increasing the bat’s weight in the on-deck circle actually slows down your swing in the at-bat! This finding goes against common practice, so why might this be? What are players doing that might lead to this?
A 2015 study by sports scientists at the American Sports Medicine Institute in Birmingham, Alabama, endeavored to find out. They tested the effects of changing the center of mass of a baseball bat on players’ swings, moving it both down towards the handle and up towards the barrel. For the testing, they gathered 30 collegiate baseball players from Division I and Division III schools, and used a standard balanced bat, a handle-weighted bat, and a barrel-weighted bat. From the players’ swings they measured the movement of the bat, the forces exerted by the players’ feet, and the timing of the players’ swing.
The study found that both the handle-weighted bat and the barrel-weighted bat differed from the standard bat in some parts of the swing. However, both of these modified bats deviated in different ways. The barrel-weighted bat diverged from the swing path of the regular bat, whereas the handle-weighted bat diverged from the swing timing of the regular bat.
Back to the physics. Recall that adding a doughnut moves the center of mass down the bat and turns it into a heavily barrel-weighted bat. This study’s results show that because a barrel-weighted bat changes the swing path of the hitters, it is not an effective way to warm up for an at-bat. This is also why it slows down the swing of batters when they are actually facing the pitcher in an at-bat – changing a swing in the moment harms the hours of training that led to the hitter’s familiar swing path. This unfamiliarity – whether perceived or not – detracts from performance. After all, the hitter doesn’t have much time to swing.
So, what’s a player to do? How can they get that feeling of ‘lightness’ that a doughnut seems to provide? An additional study from researchers at the California State University says to swing a handle-weighted bat because it does not negatively affect a player’s swing, but does give the psychological effect of swinging a heavier bat.
