The 104 MPH Fastball: How Baseball's Velocity Kings Are Pushing the Limits of Human Biomechanics

On June 12, Milwaukee Brewers right-hander Jacob Misiorowski unleashed a 104.5 mph fastball to strike out Philadelphia's Kyle Schwarber, setting a new record for the fastest pitch ever thrown by a starting pitcher in the pitch-tracking era.[1]

A week later, on June 19 against the Atlanta Braves, Misiorowski proved the milestone was no anomaly, hitting 104.2 mph and throwing 47 pitches over 101 mph.[2]

While relief pitchers have occasionally touched these extreme speeds—most notably Aroldis Chapman's all-time record of 105.8 mph in 2010 and Ben Joyce hitting 105.5 mph in 2024—starters have historically paced themselves to survive deep into games.

Misiorowski's ability to maintain triple-digit heat over nine innings—he threw a staggering 58 pitches at 100 mph or faster during his complete-game shutout of the Phillies—represents a paradigm shift in how starting pitchers are conditioned and deployed.

But as the radar gun readings climb, a fundamental question emerges from sports science laboratories: How is the human body generating this much force, and is there a hard biological ceiling?

The answer begins far away from the throwing arm. Biomechanics experts emphasize that a 104 mph fastball is not the product of sheer arm strength, but rather the efficient transfer of energy through the body's "kinetic chain."

The sequence starts with ground force. Pitchers generate massive power from their legs and hips, creating rotational torque that travels up through the core and into the shoulders.

As the torso rotates toward home plate, the throwing arm lags behind in a phase known as "arm cocking." The arm externally rotates to extreme angles—often 160 to 180 degrees from the horizontal—stretching the muscles and ligaments like a drawn bowstring.

It is at the exact end of this cocking phase that the arm experiences its maximum stress. According to Dr. Glenn Fleisig, research director at the American Sports Medicine Institute, the torque on the elbow reaches roughly 100 Newton-meters.

To put that abstract number into perspective, Fleisig notes that the stress is equivalent to a pitcher holding a 60-pound weight in their hand while their arm is cocked back.

The primary structure bearing this immense load is the Ulnar Collateral Ligament (UCL), a small band of fibrous tissue in the elbow that stabilizes the joint during the throwing motion.

Biomechanical testing on cadavers has revealed a sobering reality: the amount of torque required to throw a baseball at 100 mph or faster is right at the absolute limit of what the human UCL can withstand before tearing.

"We are at the maximum limit of velocity because we are at the limit of what the UCL ligament can handle," Fleisig has noted, explaining why peak velocity across the league may eventually plateau even as average velocity rises.

The violence of the pitch does not end when the ball is released. During the deceleration phase, the shoulder must absorb the extreme speed it just generated, experiencing angular velocities of nearly 7,000 degrees per second—making it one of the fastest known human motions.

This split-second deceleration requires the rotator cuff and labrum to absorb hundreds of pounds of compressive force, explaining why shoulder and elbow injuries remain a constant threat for high-velocity throwers.

Despite the biological red lines, modern training regimens, weighted-ball programs, and high-speed camera analysis have allowed pitchers to optimize their mechanics to safely skirt the edge of human capability.

For now, athletes like Misiorowski and Joyce continue to redefine what is possible on a baseball diamond, turning every pitch into a high-stakes physics experiment that captivates fans and scientists alike.[1]