How Should Extension Be Used?

I hear people talk about extension all the time, but rarely do I see people explain how to functionally extend and what purpose it should serve. So I thought I’d take a crack at it. 

Let’s first discuss how extension is typically taught. Usually extension is taught as a way to generate more power in the swing, hitter’s are taught to extend their arms though the pitch as it approaches the plate.

While extension is a component of many great swings kids are often taught to extend too early in their movement pattern, this results in swings that are inefficient. In reality, the vast majority of hitters are limited by how fast are able to turn their torso while retracting their scapula. The turn of the torso is what typically creates bat speed and also allow for mass to be added to your swing, since the center of your body is where most of your body’s weight lies. After the turn of the torso has begun, then the hitter’s arms can extend. Too often, kids are taught to extend their arms before their torso is turned.

Check out Josh Donaldson’s swing below to see how he uses his body and when he begins to use his arms.

Hips First

Torso Turn Second

Hands/Arms Last

Full Swing Through Contact

You can see in the last 2 GIF’s how Donaldson uses his arms/hands. It happens after the hips turn and the torso begins to turn. This allows for the best control of the barrel as the bat goes through the zone and for the barrel to enter the hitting zone deep (by the catcher’s mitt). In this case, Donaldson doesn’t fully extend and we can see from the first 2 GIF’s that Donaldson doesn’t really use his hands/arms to get his barrel started into the zone. His arms are more used to go get the ball once the torso is turned and the bat is already in the zone. The order of the movements that all hitters make is very important. Kind of like in math there is an order of operations, For efficient energy transfer from the ground all the way to the barre parts of the body that are closer to the ground should move first so the energy from the ground have time to be passed up the kinetic chain to the barrel. For this reason, extension of the arms has to be the last link in the chain.  

In some swings, extension doesn’t even happen, in others it does. If used, it’s a tool for adjustment to pitches in unexpected locations and unexpected speeds.

Here are some hitters both using extension and also some not using extension. The point isn’t to say that some hitters extend and some hitter’s don’t the point is to say that on any given swing, extension may or may not happen. It a tool that can be used but it isn’t always used.

Examples of Hitters Using Extension

Manny Machado

Juan Soto

Christian Yelich

Aaron Judge

Aaron Judge

Examples of Hitters Not Using Extension

Matt Wieters

J.D. Martinez

Mike Trout

All of the videos above, extension or not, were swings that produced home runs. We can see that extension isn’t always needed to generate power. That said, in all the videos above the hitters turn their body. The turn of the body, and how fast it’s done is really the key for generating power in the swing.  

You might be asking the question, why is extension early in my movement sequence bad?

Well there’s essentially 4 reasons that early extension is bad.

1)If you extend early, it can result in a swing thats excessively down. If a hitter were to extend their arms immediately in their swing the direction of that extension would be down to any pitch other than the highest strike possible. This is not ideal, and will cause a lot of glancing blows, ground balls, and misses.

2)Thoughts about early extension can create front arm bar, leading to slipping of the back elbow/bat drag. When young hitters think about early extension they end of barring their front arm. This results in the hitter reaching their hands over home plate and slipping their back elbow between their rib cage and their hands. As shown below, the slipping of the back elbow stops the bat from turning into the path of the pitch (bat drag).

3) It reduces the mass used in your swing. Excessive arm use early in the swing can result a reduced amount of mass used in your swing which can reduce the overall force output. Force = Mass X Acceleration.  So If in swing A: a hitter turns from the center of their body efficiently and the mass used in the swing is 100 units (this number is arbitrary) with an acceleration of 20 units (also arbitrary) it results in a force output of 2000 Units (only for comparative purposes).

If in swing B: the hitter used their hands more their turn from the center of their body will likely be less efficient since according to Newton’s Third Law every action has an equal and opposite reaction extra early arm use early in a swing applies equal force back on the back shoulder (the force’s origin) slowing the turn of the hitter’s trunk and ultimately reducing the weight (mass) used in the hitter’s swing. Often this reduction in mass used can be enough to greatly reduce the force the bat can exert on the ball. If the extra arm use increases acceleration by 10% and decreases mass by 10% the net result is less force available to hit the baseball with.

Swing A = 100 Mass Units X 20 Acceleration Units = 2000 Force Units

Swing B = 90 Mass Units X 22 Acceleration Units = 1980 Force Units  

4) Full extension causes rollover, leading to an bio-mechanically unsupported impact position. Ideally we don’t want to rollover if we can help it because rollover puts the back arm in a position that puts it at risk for injury if enough force is applied against it. Check out the way these lumberjacks impact the piece of wood they are cutting below.

Check out the below contact position, see how his back forearm is behind the handle of the axe at impact? If it wasn’t, if he was fully extended much of the force of impact will be absorbed by the inside of his arm, and would put a ton of stress on the UCL.

Just think if I were to try and chop down a tree like the picture on the below right how much stress I’d be putting on the inside of my right arm by my UCL.

On the left it’s possible for the force from the tree to be passed back into the center of my body for absorption on the right there’s no way that’s possible.

If you grabbed an axe and tried to cut down a tree like the picture on the right your body literally wouldn’t let you. The brain and body are a lot smarter than we give them credit for it won’t consciously do things that will result in your injury when being injurious is not your intent.  

Also when you extend and rollover you lose all adjustability. Your extension is your mid-swing adjustability!

This explanation works better visually, so check out the below video if you want to learn more.

For all the above reasons, I typically wait a solid amount of time before I even talk about extension with hitters. If your turn isn’t very good any extension that you get in your swing won’t be functional. 

If you read this article and you start working on your swing or kids’s swing. Please use video, it’s so easy to use video now there’s no excuse not to. The longer I work with hitters, the more I realize that what hitter’s feel is happening can be very misleading. Often video doesn’t align with what the hitter thought they did,  It’s important to understand that feel can be a very useful tool for a hitter, but it works best when it’s calibrated by video.

Thanks for reading!

Kurt Hewes

Kurt Hewes – Founder of Ignite Baseball

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