The Foundations of Arm Care: Eccentric Muscle Contractions

by Chris McKenzie PT, DPT, OCS, SCS, PES


Do you want to know how to prevent a SLAP tear, or any significant injury from happening as a baseball or softball player?

I thought so…

Enter Chris, a 15y/o left handed pitcher who was throwing good heat for his age (sitting in the low 80’s) without any formal pitcher training. Chris began developing a painful pinch on the back of shoulder early in the Spring of 2014 in the late cocking position. This pain eventually brought him to my clinic, where he could only crow-hop a 90ft throw before he experienced his painful pinching. I gave Chris some simple exercises to perform and 2 weeks later here’s what happened:

Long Toss Distance: 180ft without pain or pinching (a 200% improvement in distance, without pain)

Pitching Velocity from the mound: Not tested, but Chris said he was throwing at 85% without any pain or pinching.

Sure, you might be thinking to yourself, “85% of his usual low 80’s isn’t throwing heat, and that’s NOT impressive.”…and you’re right…about the heat.  What IS impressive is that Chris was then diagnosed with a very large SLAP tear, which he eventually had surgically repaired and rehabbed.  Let me say it again a different way:  Chris was able to throw 180ft pain free with a large SLAP tear after only 2 weeks of simple exercises.  Had he been doing these exercises since he began competitively pitching, surgery may have been avoided.

What happened?

In order to throw heat, and long distances with known shoulder pathology, or to prevent these injuries from happening in the first place, specific parts of the body must be trained with an eccentric muscle contraction.  Maybe you’re thinking to yourself, “What the heck is an eccentric muscle contraction?”


An eccentric contraction of a muscle is when the muscle is lengthening, but still contracting. In many gym-goers, it’s also referred to as a “negative.” Think about pulling milk out of the fridge and what happens to the biceps; the bicep pops right up.

In this case the bicep is shortening–also known as a concentric contraction. It’s when you put the milk back in the fridge that the Biceps lengthens under a load.  Lowering that milk back into the fridge represents an eccentric contraction of the biceps. If you didn’t slow that arm down the milk would likely spill, as your arm would come careening downward onto the shelf.

Now think of a baseball pitch, or throw. What kind of muscle contraction do you think slows down your arm from being ripped off your body?  Yes! Eccentric contractions!

Are you training your body to slow down, or just go fast?

With baseball throwing, most injuries occur in:

The deceleration and follow through phases when you release the ball:


I’m not saying you won’t feel pain elsewhere, but this is a prime spot in baseball throwing where pain and injury occur.  Can you guess what type of muscle contractions are occurring in this position?  That’s right…eccentric contractions. This is simple science, and here are two articles of many (article 1,  article 2) that show clear as day, eccentric muscle contractions are occurring.


Rewind to the early 1980’s, Frank Jobe, M.D. (he invented Tommy John surgery) did EMG (Electromyography—the study of muscle activation) studies of muscle contractions on the throwers shoulder (study 1, study 2)–his results were much like today’s results; showing spikes of muscular activity during specific portions of the throwing phase, especially in the deceleration and follow-through phases. And getting a little more in depth, if you know anything about muscle origins and insertions, you know what type of muscle contraction is occurring at any phase, or point in time of the throwing motion.


Again, if you know your muscle origin, insertion and primary action, graphs like these blurt out where the eccentric muscle contractions are occurring. If you don’t that’s fine…I’ve got you covered!

Wait! There’s more…

Nobody ever said eccentric muscle contractions are limited to your shoulder. In fact, that couldn’t be further from the truth.

A friend of mine, Lantz Wheeler, said that to generate arm and ball velocity, your initial goal should be to move your center of mass as far and as explosively away from it’s starting point as you can–so you can generate a long stride. You need strong, powerful legs to get “the ball rolling.”  (Quasi-pun intended) In short, we need to generate much speed and velocity with our legs to speed up our center of mass.  This is more difficult for pitchers, and obviously easier for position players like outfielders as they can get a running or hopping start.

Center of Mass

Now, that center of mass needs to slow down unless

you plan on running forward after you throw, or pitch. How often does that happen?!

How to put it all together: Concentric and Eccentric Throwing Explained.


The Concentric Process

The center of mass speeds up, and passes it on to the trunk/torso/core (choose whatever term you like best).

The trunk, acting as a velocity conduit to the arm, speeds up via rotation and flexion (hence the need to practice linear into rotational power training).  The trunk passes this velocity onto the shoulder, and finally the elbow and wrist.  Concentric muscle actions are responsible for moving *most* of the velocity in a throw, forward, from that initial leg drive to ball release.

[*For you astute people—eccentric contractions do play a role in helping to create joint stiffness to aide the concentric process]

Now remember…eccentric contraction = arm health. As one body part speeds up, the one right behind it automatically slows down–this is an automated response by your body.  However, this deceleration must be purposefully trained with strength training overload principles if you want to have good arm health now and in the future.  Specific deceleration movement patterns should also be trained with a throwing coach who is skilled in deceleration mechanics.

The Eccentric Process

The slow down of the center of mass begins just after the stride leg foot contacts the ground. Eccentric contractions begin with the hamstrings, then glutes (hip abductors, external rotators and extensors) as the pelvis rotates toward the plate.

Here’s that proof again (Campbell 2010):

Leg muscle EMG during throwing. “Phase 3 in this study is when the stride leg foot hits the ground. “Phase 4 is just after ball release.

As your core speeds into rotation and flexion, and passes that velocity to the shoulder–the back muscles (too many to list!) eccentrically contract to control the forces that go through your shoulder. Your shoulder passes the velocity down to an elbow that is just beginning to straighten, as the posterior rotator cuff muscles are now eccentrically contracting. The elbow is now rapidly extending and the bicep and elbow flexors work to decelerate this action. Combined with all 4 rotator cuff muscles, the bicep also resists/protects your arm from being ripped off your body as the ball is hurled away from you (this is known as a traction force that your body is actively resisting—the ball of your shoulder [humeral head] is actually being pulled forward and out of it’s socket ever so slightly.) Lastly the wrist extensors eccentrically contract to slow down your wrist into end range wrist flexion and forearm pronation.

So what happens when you’re deficient in eccentric strength?

When you lack eccentric strength and you continue to throw hard, abusing those deceleration muscles—The weakest link usually hurts, AND (this is important!) it puts more strain on the next segment down the chain causing risk of significant damage.

If you think feeling sore after you throw is normal, think again. The guys that train with my arm care program rarely complain of soreness after they throw hard. They have learned the value of eccentric training for about 30min, on a daily basis and practice eccentric training.

And of course, proper mechanics is of the utmost importance for long-term injury prevention. Still, remember Chris from earlier? He had terrible mechanics (sorry Chris– but you know it!). He achieved his 200% increase of pain free throwing even without changing his faulty mechanics. Eccentric training can take you far, even to the point of “hiding” aches and pains from poor mechanics, but the crap always floats to the top…and it will come back to bite you some day. So get your mechanics checked!

So now you know what to do. Eccentrically strength train from the hip, down to your wrist.

Need some help with eccentric training? Want to learn more about arm care? Contact Dr. Chris McKenzie at

What you do think? Leave a comment below. Did you like this article? Share it with a friend!


Chris McKenzie is a double board certified sports and orthopedic physical therapist for players in the MLB, MiLB, NCAA and youth baseball. He is the owner of McKenzie Sports Physical Therapy in Pennsylvania, an Adjunct Professor and Clinical Specialist at Drexel University in Philadelphia. Chris can be reached at

The Foundations of Arm Care: Eccentric Muscle Contractions Comment

  1. If your elbow always has to be above your shoulder, how to submarine style pitchers achieve this?
    I’m screaming body tilt at the top of my lungs.

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