The latissimus dorsi (lat)  is a very powerful muscle. It plays a very big, very important  role in throwing a baseball, it also can be a very big problem. We have seen an increase of injuries in the MLB from the past. This is due to the fact that velocities are at a higher average than they were 20 years ago, as well as athletes take training much more serious in their quest to gain velocity. 

 A little bit about the lat and its actions
It is large, flat and triangular in shape. A very poweful muscle and plays a big part in throwing a baseball.

Action of The Lat

  • Adduction of the humerus
  • Internal Rotation of the humerus
  • Arm Extension

First what we need to realize not everyone’s lat is the same as far as where it attaches. Most of the time the lat’s orgin looks like this…

  • Lower Back (Lumbar Spine) 
  • Thoracic Spine (t-7 to T-12)
  • Iliac Crest and Sacrum 
  • Inferior Ribs 3 and 4
  • Inferior Angle of the Scap

A lot of times, the lat gets confused with the teres major in throwing injuries. These two muscles are often grouped together when an injury is present due to the fact they both run closely together near the armpit to the front of the shoulder.  A lot of time, with athlete presenting anterior shoulder pain, clinicians will diagnose the athlete with biceps tendonitis when in actuality it could be a referral pain from the teres or the lat. The lats insertion is at the bicipital groove of the humerus while the teres attaches next to it.
 Having a lat altered in length can change how the posture of the body or how the body moves. 

Reasons we see lat issues in baseball

  • Overuse 
    • Throwing more causes increased external rotation which will decrease internal rotation. The lat will decrease in length while in over-head flexion. Normally if the lat is tight], pain will be present in the layback portion of the arm
  • Eccentric Tension of the throwing motion
    • Transfer of forces from ER to IR will damage the lat in even a healthy shoulder. Excessive external rotation (ER) will cause more and more injuries if the athlete is unable to control stability where needed. The average ER 110 degrees for a Healthy arm and now we often see an increase to 150 degrees in a lot of harder throwers. This forces the lat to create eccentric control of the arm going into layback, guys without end-range stability as well as adding the fact that the players of today are much more powerful than even a few years ago can cause a serious injury.
    • We see this especially in the youth population while their bones are continuing to change. Unwanted boney changes may occur with the amount force needed. 
  • Lack of Over Head Flexion
    • If the lat becomes tighter the more you throw, the less OH flexion you will see in the athlete. A short lat can drive the athlete into lumbar extension, flare the ribcage, depress the scap and clavicle, depress the hip or even cause issues with pronation and supination. 

As we will never be able to prevent injury, we can reduce the risk of injury. This starts with educating coaches, players and athletes. If we can present knowledge of proper arm care and training programs for the baseball player, we will start to make changes and decrease the amount of injuries seen in the game. 

Strength programs need to address

  • Restore tissue quality
  • create programs that address mobility or stability in separate athletes
  • Learn what time of year to program certain exercises
  •  Create more core stability
  • Create more athleticism
  • Increase Dynamic Stability

Learning the basic anatomy of the body as well as their physiological demands of throwing a baseball will help decrease your chance of injury. Next time you are having arm issues or feel discomfort find a professional to help you. The worse thing we can do is to continue to throw through the pain. Throwing a baseball should be relatively pain free.

DJ Edwards