by Dr. Michael D. Chivers

The baseball pitching motion involves the coordinated movement of the lower extremity, trunk and upper extremity. The action of the throwing arm is the fastest recorded motion in all of sports. From the biomechanical data available we now know that the shoulder angular velocity can reach anywhere between 7250 °/s to 7265 °/s in Major League pitchers.*

This repetitive motion performed over the course of multiple innings in the case of a starter, can potentially lead to muscle fatigue that could impair performance, cause mechanical alterations or compensations, and ultimately overuse injuries.


Considering the large body of articles and research on the biomechanics of pitching, there is a paucity of papers dedicated to the effects of fatigue on pitching.

Barrentine et al were the first group to investigate the effects of fatigue on performance. During simulated game situations, their group of college aged pitchers demonstrated a decrease in shoulder abduction in the arm cocked position, in essence a “dropped elbow” and they found a decrease in lead knee flexion at the instant of ball release.*  The researchers determined that these alterations began to occur as the pitcher approached muscular fatigue in the later innings.


Murray et al examined the effects of fatigue on MLB pitchers during actual game play during the 1998 and 1999 seasons, using high speed cameras on both baselines and overhead behind home plate and digitized markers on the pitcher`s body. Pitchers who pitched at least five innings were those whose data were analyzed. 

It was found that seven biomechanical parameters changed as the pitcher continued to pitch....

1. Ball velocity
2. Max external rotation at ball release
3. Knee angle at ball release
4. Max shoulder distraction force
5. Max elbow distraction force
6. Horizontal abduction torque at ball release
7. Max horizontal abduction torque

Most importantly, during the later innings the pitchers demonstrated less external rotation of the throwing shoulder (unable to achieve a full cocking position), increased lead knee flexion at the point of ball release. Not surprisingly they also found that ball velocity decreased in the later innings by an average of 5 mph.

Note: The latter 4 variables I did not include because they are not "visible" to the naked eye and would need some explaining [beyond the scope of this article].


Numerous investigations performed out of the American Sports Medicine Institute (ASMI) between amateur pitchers and professional pitchers and among American and Korean pitchers have shown that the greater external rotation of the throwing shoulder in the cocking position and the ability of the pitcher to quickly straighten the lead leg to act as a brace and allow the trunk to rapidly flex forward are two of the most important mechanical considerations to impart velocity to the ball.

In addition, Murray et al found that shoulder joint and elbow joint distraction forces increased. Simply this means that as the muscles around the shoulder and elbow fatigued, the joint structures themselves (i.e bones, ligaments, cartilage) had to withstand greater forces. This has important injury consequences as it is apparent that the shoulder and elbow are the most injured areas in MLB pitchers and cause the most days spent on the disabled list.*


Mullaney et al in a recent investigation, using college aged pitchers, on muscle strength before and after a pitching performance found that there was significant fatigue in the shoulder muscles, primarily those that accelerate the arm forward and in the rotator cuff muscles. It is evident from this data that the muscles surrounding and acting on the shoulder experience a high energy demand during pitching and are susceptible to significant fatigue. 

Macrina et al reported in their investigation that as MLB pitchers became fatigued the position of the scapula (shoulder blade) worsened leading to an increase in movement away from the spine which ultimately impairs the transfer of energy from the lower body and trunk to the throwing arm.  This would not be appreciated visually by the coach, however a sharp change in velocity or control can be a sign of improper shoulder blade mechanics.

There are numerous studies documenting dysfunction of the scapula termed “scapular dyskinesis” in the throwing shoulder and serious pitching injuries such as labral pathology and impingement lesions of the shoulder and ulnar collateral ligament injuries of the elbow. It is important from a “pre-habilitation” and strength and conditioning perspective that we train our pitchers shoulders to prepare for this fatigue effect on the throwing arm.

Most recently, Escamilla et al in a laboratory setting using digitized high speed cameras found that after throwing 15 pitches for 7-9 innings the pitchers demonstrated a trunk position that was close to vertical rather than forward flexed at the moment of ball release. In addition, ball velocity dropped significantly during the last 1-2 innings pitched.

As was mentioned above greater forward trunk tilt contributes to increased ball velocity and it also helps to dissipate some of the forces on the throwing arm during the deceleration phase. With a more vertical trunk, the pitcher tends to throw with too much arm and ultimately increase the risk of injury.


It is important to understand that it is very difficult to determine how many pitches a pitcher can throw before fatigue becomes an issue and potential injurious mechanics start. Simply, muscular fatigue is a state in which the capacity of a muscle to produce maximum voluntary action, or to perform a series of repetitive actions, is reduced. In the case of some starting pitchers they will show no ill effects after throwing 100 or more pitches while others start to fatigue after throwing 60 pitches. Muscular fatigue is very subjective for the most part and currently there are no objective measures that can be used on the field to assess the level of fatigue of a particular pitcher.

It is for this reason that in Little League baseball there are strict pitch counts and rest intervals to limit the potential for excess fatigue and injury. 


There are many factors to consider when it comes to fatigue. Some of those are...

• the overall health status of the pitcher,
• type of conditioning and training employed,
• amount of rest between outings,
• type of pitches thrown,
• other in-game factors such as...
  
  • amount of pitches thrown per inning,
  • pick-off throws,
  • any excess running or fielding done by the pitcher.

 
The results of these studies have enormous implications for all those involved in the care of the overhead athlete, from the therapist, strength coach and pitching coach. A thorough knowledge of the changes that occur as the number of pitches increases provides valuable information regarding how long a pitcher can throw before mechanical breakdowns start to happen which can eventually lead to performance decrements and the potential for injury resulting in substantial time spent on the disabled list.