Overload/Underload Bat Training
Also known as: overload underload training, overload/underload bat training, weighted bat training, do weighted bats increase bat speed, heavy and light bat training, underload training
Overload/underload training means swinging implements heavier and lighter than your game model over several weeks to build swing speed. Studies with baseball players have found speed gains from programs that mix the two with normal swings. Most programs stay close to game weight. Young players should use light loads, low volume and adult supervision.
Heavier implements train force and lighter ones train speed. Alternating them with game-model swings challenges the swing at both ends. In a 1995 study by DeRenne and colleagues, 60 college baseball players were split into groups. Training with overweighted and underweighted implements, as dry swings or in batting practice, raised swing velocity. The control group also improved. That means the size of the effect needs care.
Programs vary. Most share a few habits. Loads stay near game weight, every rep is full intent, and sets are short with rest between them. Many hitters run a block of several weeks in the offseason. They end a set as soon as form slips.
For young players, technique comes first. A heavy implement can pull a swing out of shape. Many coaches start youth hitters with lighter-than-game models and fast swings. A 2019 study found that dry swings with a light model increased swing speed. Stop if anything hurts, and see a qualified medical professional for pain that does not go away.
Tips by skill level
Keep any heavier model close to your game weight. Stop the set when your swing gets sloppy.
Test game-model speed on the same sensor before and after each block. Keep reps full intent and rest between sets.
Example
A sophomore catcher follows a six-week winter block three times a week. Each session pairs a heavier model, a lighter model and his game model in short, rested sets. His sensor readings with the game model climb a few mph by the first scrimmage.
Why it matters
Swing speed drives exit velocity. This kind of training is one of the more common ways to build it.
Common mistakes
- Choosing an implement far heavier than game weight
- Grinding through sets with sloppy form
- Starting a new block in-season right before games
- Giving kids heavy implements before their swing is stable
Frequently asked questions
Do weighted bats increase bat speed?
Programs that mix heavier and lighter implements with normal swings have shown speed gains in studies of baseball players. Swinging a heavy one right before you hit does not.
How heavy should an overload bat be?
Most programs keep it only a little heavier than your game model. If it changes your swing, it is too heavy.
Is overload underload training safe for kids?
It can be with light loads, low volume and adult supervision. Many coaches start kids with lighter models. Stop if anything hurts.
Sources
Related terms
- Weighted Bat Warm-UpSwinging a donut-weighted or heavy bat on deck makes your game bat feel lighter, but studies have not found that it makes your swing faster. In lab tests, a heavy warm-up left the next swings with a normal bat no faster, and sometimes slower, even though players felt quicker. A few hard swings with your game bat, or a lighter bat, prepare you at least as well.
- Bat SpeedBat speed is how fast the barrel is moving at contact, in mph. It contributes to exit velocity alongside bat path and where on the barrel you make contact.
- Strength Training for Bat SpeedStrength training can raise bat speed by building the legs, hips and trunk that drive the swing. Many programs pair basic lifts such as squats, hinges and presses with rotational medicine-ball throws done at full speed. Young athletes should learn form with light loads under qualified supervision.
- Offseason and In-Season Hitting PlanAn offseason hitting plan builds strength, bat speed and any swing changes while there are no games. An in-season plan keeps the swing sharp with less volume and more game-like work. Many programs take a short rest after the season, then build from tee and strength work toward live pitching before spring.
- Bat Speed by AgeBlast Motion, a bat-sensor maker, publishes practice-swing ranges of about 30–45 mph for 8- to 10-year-olds and 40–52 for 11- to 12-year-olds. For older players its ranges are about 46–62 mph at 13–14, 55–65 at 15–16 and 60–70 at 17–18. Treat them as rough guides from one sensor in tee and toss work. In MLB, Statcast's average swing was about 72 mph when bat tracking launched in 2024.
Related guides & benchmarks
Have a question about this?
There is nothing here to film. Ask SwingVantage a follow-up question, or keep reading the related terms above.