Why Sir Isaac Newton is Still the Foremost Expert in Pitching Biomechanics


This post was written by Dr. James Buffi.

Most people have heard of Sir Isaac Newton and his famous laws of motion. Most have not heard that he was an expert in modern pitching biomechanics.

So let’s talk about how Newton’s most famous law relates to pitching.

Newton’s most famous law of motion is probably F = ma. Force equals mass times acceleration.

This law dictates that the acceleration of an object, like a baseball, is dependent on both its mass and the outside forces acting on it. F = ma is the foundation of all mechanical analyses and therefore it’s important for pitchers (and really all athletes) to understand what it means.

In F = ma, the “m” stands for mass. Mass is a measure of how much matter, or “stuff,” an object contains. An object can be really large in volume but have very little mass, and vice versa.

A blimp is huge, but relatively speaking, it does not have as much mass as one would expect because it is filled with gas. The mass of a typical baseball is 145 grams, which weighs about 5 ounces.

Next, let’s look at the “a” in the equation. The letter “a” in F = ma stands for acceleration. To understand acceleration, it is best to start by understanding the concept of distance. Distance is the space between two points. For example, the distance between the pitching rubber and home plate is 60 feet 6 inches.

Velocity measures distance traveled per unit of time. So a 95 mile per hour fastball can travel 95 miles in one hour. 95 miles per hour is about 140 feet per second. In other words, it takes less than half a second for a 95 mph fastball to travel from the pitcher’s hand to the catcher’s mitt.

Acceleration measures how much velocity is changing. It measures the rate of change in velocity. The size of the acceleration, the amount of time over which it occurs, and the initial velocity, determine an object’s final velocity. The concept of acceleration is a little trickier to understand than velocity. It is measured in distance per time, per time.

For example, in a pitching motion, the acceleration of the baseball could be 95 miles per hour, per second. In this case, the velocity of the ball would change from zero mph (i.e. not moving) to a velocity of 95 mph (i.e. moving really fast) in one second.

The acceleration phase of a pitching motion, in which the ball accelerates from rest to its release velocity, is generally much shorter than one second. The fastest cars in the world accelerate from zero to 60 mph in several seconds… so, in this way, the body can accelerate faster than an Italian sports car.

Now how do we cause an object with mass to accelerate?

We apply a force to it. This is the meaning of F= ma. An object will accelerate as long as there is net force acting on it.

And the size of the acceleration is dependent on the amount of mass and the size of the force. For the same net force, an object with less mass will accelerate more than an object with more mass.

A force can be thought of as a push or pull on an object. In the baseball pitching motion, the hand applies a force to the ball by “pushing” it. This causes it to accelerate from rest to its final velocity at release. In a similar manner, the forearm applies a force to the hand causing the hand to accelerate. The upper arm also applies a force to the forearm, and so on down the kinetic chain of body segments.

The force that one body segment exerts on another is transmitted through a wide variety of structures, including bones, muscles, and ligaments. One of the ligaments through which force is transmitted from the upper arm to the forearm is the ulnar collateral ligament (UCL).

As I’ve said before, for a specific pitcher, it remains unclear how much force is felt specifically by the UCL during each individual pitch. Researchers have attempted to gain a better understanding of UCL loading during pitching by calculating the total force load on the elbow under a variety of conditions. They’ve done this using an approach called inverse dynamics.

Researchers have calculated the total elbow load experienced by youth, high school, college, and pro pitchers [1-6]. They have calculated and compared the total elbow load for fastballs, curveballs, sliders, and change ups [7-9]. They have performed many similar studies and this is what they’ve found: F = ma.

Unless a pitcher totally changes his or her pitching motion, the only way to substantially increase the final velocity of a pitched baseball is to increase the magnitude of its acceleration. And the only way to increase acceleration is to apply a greater force.

Hence, the aforementioned studies have shown that when pitchers throw regulation baseballs faster or farther, they experiences greater total elbow forces.

In essence, they’ve shown that to increase “a” one must increase “F.”

This academic literature is a primary reason why some believe curveballs are less dangerous than fastballs. Curveballs are thrown with less velocity and thus require less force. This literature is also why some coaches are hesitant to include long toss in training routines.

It is true that faster pitches and longer tosses generally require increased elbow loading. However, the total force on the elbow is not the force on the UCL. I firmly believe that pitchers can safely throw faster and farther with proper training and without drastic changes to their pitching motions.

The ligaments are not the only structures crossing the elbow. Many muscles do as well. And the primary purpose of these muscles is to transmit force.

Despite the biological complexity of joints like the elbow, there is a severe lack of anatomical and physiological considerations in most modern discussions of pitching biomechanics. People may talk about things like arm slot and forearm pronation, but they don’t talk about muscles, bones, and other connective tissues.

To summarize where the field of pitching biomechanics currently stands, it has been confirmed that F = ma. We have confirmed that Sir Isaac Newton’s most basic law still holds during the pitching motion. He is still the foremost expert in pitching biomechanics.

Now we need to press onward. It is time to stop focusing so much on total force and total torque (torque is the rotational equivalent of force).

Instead, we need to understand how total force is distributed among the internal structures of the body (i.e. muscles, bones and ligaments). We need to know how these internal structures are able to produce 100 mph fastballs and not break. Let’s incorporate some anatomy and physiology into our biomechanical studies of pitching. Maybe focus a little more on the “bio” in biomechanics.

Knowledge of force is important, but knowledge of how this force interacts with human biology is just as critical. The body is made of adaptable, living tissue. We should analyze it accordingly.

The following are some physiology-based questions I am currently considering using computational modeling techniques.

  • How hard are individual muscles working during each pitch for a specific pitcher?
  • How much force is actually felt by the UCL during each pitch?
  • Which muscles contribute the most to increased velocity?

And so on…

There are countless essential questions remaining unanswered about human physiology during pitching. These questions make it a very exciting time for researchers, like me, who are fascinated by the complexity of the body… and also love baseball.

Dr. James H. Buffi has a degree in mechanical engineering from the University of Notre Dame and a PhD in biomedical engineering from Northwestern University. His doctoral dissertation was called, “Using Biomechanical Modeling and Simulation to Calculate Potential Muscle Contributions to the Elbow Varus Moment during Baseball Pitching.” He has also been a visiting scholar in the National Center for Simulation in Rehabilitation Research at Stanford University as well as a visiting researcher at Massachusetts General Hospital. You can follow @jameshbuffi on twitter.


  1. Fleisig, G.S., et al., Kinetics of Baseball Pitching with Implications About Injury Mechanisms. American Journal of Sports Medicine, 1995. 23(2): p. 233-239.
  2. Fleisig, G.S., et al., Kinematic and kinetic comparison of baseball pitching among various levels of development. J Biomech, 1999. 32(12): p. 1371-5.
  3. Nissen, C.W., et al., A biomechanical comparison of pitching from a mound versus flat ground in adolescent baseball pitchers. Sports Health, 2013. 5(6): p. 530-6.
  4. Anz, A.W., et al., Correlation of Torque and Elbow Injury in Professional Baseball Pitchers. American Journal of Sports Medicine, 2010. 38(7): p. 1368-1374.
  5. Aguinaldo, A.L. and H. Chambers, Correlation of throwing mechanics with elbow valgus load in adult baseball pitchers. Am J Sports Med, 2009. 37(10): p. 2043-8.
  6. Fleisig, G.S., et al., Biomechanical comparison of baseball pitching and long-toss: implications for training and rehabilitation. J Orthop Sports Phys Ther, 2011. 41(5): p. 296-303.
  7. Escamilla, R.F., et al., Kinematic comparisons of throwing different types of baseball pitches. Journal of Applied Biomechanics, 1998. 14(1): p. 1-23.
  8. Fleisig, G.S., et al., Kinetic comparison among the fastball, curveball, change-up, and slider in collegiate baseball pitchers. American Journal of Sports Medicine, 2006. 34(3): p. 423-430.
  9. Nissen, C.W., et al., A Biomechanical Comparison of the Fastball and Curveball in Adolescent Baseball Pitchers. American Journal of Sports Medicine, 2009. 37(8): p. 1492-1498.

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