The 100mph fastball used to be a rarity: now it’s an everyday occurrence in Major League Baseball. But the human body may not be built for such speeds

Sidd Finch was almost too good to be true. The rookie pitcher, while in spring training with the New York Mets, was reported to have shattered pitching records by throwing a 168mph fastball with pinpoint accuracy. Proclaimed as a yogi and virtuoso on the French horn, Finch was in fact, too good to be true, the subject of an elaborate April Fools’ Day hoax by sports writer George Plimpton and Sports Illustrated.But the Finch story serves as a reminder that speed captivates our attention like few other sporting attributes.

Once upon a time, throwing a pitch faster than 100mph was rare, the four-minute mile of baseball. That is, until Cuban émigré Aroldis Chapman, pitching for the Reds, Cubs and Yankees, made 100mph fastballs commonplace. Others have yo-yoed above and below triple digits, but Chapman has beaten the 100mph barrier pitch after pitch, game after game, and season after season. Just as Roger Bannister’s mile opened the floodgates for other four-minute milers, Chapman seemingly paved the way for a new generation of flamethrowers.

Chapman and Jordan Hicks – the two players who share the record for fastest pitch at 105mph – now offer up only a fraction of the pitches thrown at 100mph+, a number that has more than doubled in the past 10 years. While showing signs of leveling off, average fastball velocity has also increased, adding nearly 2mph in the same period. It should also be noted that speed alone doesn’t make a great pitcher. Hyun-Jin Ryu, arguably the best pitcher in baseball this season, maxes out in the low 90s.

Part of the magic of velocity is that those gifted with a golden arm come by it through different paths and with assorted body types. Some, like Mark Wohlers, who hit 103mph while pitching for the Atlanta Braves, had it all along. “I think I always threw harder than kids my age growing up,” says Wohlers. “I was probably above average until I reached the minor leagues and it was then that my velocity really made a noticeable jump after working with a pitching coach and the Atlanta Braves minor-league system to straighten out my mechanics.”

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For Wohlers, throwing that first pitch over 100mph was a big moment: “At the time, I felt pretty cool, because not a lot of players had done it.”

Others develop more slowly and make a jump as they get bigger and stronger. “I threw about 60mph as a freshman in high school, 70 as a junior and was at the low 90s in minor leagues,” says Conner Greene, a pitcher in the Kansas City Royals organization, “and then all of a sudden, one night I threw 97 mph.” Greene believes that once he knew he was capable of throwing that hard he was able to unlock an even greater potential, eventually hitting 103mph during the 2017 season.

If you look at the pitchers that throw the hardest, you’ll notice that there is a wide range of builds. Of course, there are the pitchers like 6ft 6in Noah Syndergaard, with his Viking physique and flowing blond hair, who look every bit the part of a flame throwing pitcher. Hicks is listed at a more modest 6ft 2in and 185lbs. That’s the beauty of baseball, says Dr Glenn Fleisig, research director at the American Sports Medicine Institute. Compared to other sports, baseball pitchers can succeed at different sizes. What those pitchers have in common, he explains, are good genetics and good mechanics.

Tall, short, lanky or muscular, it doesn’t matter. Greene believes that the ability to explosively generate velocity with a powerful, athletic motion, regardless of body type, sets high velocity pitchers like Hicks apart. “The hardest throwers have the same explosiveness as a track sprinter, even if they aren’t always the tallest or biggest.”

Part of the reason why pitchers don’t look like power lifters, is that muscle strength alone does not account for the velocity created when pitching. In fact, muscles only contribute about half the required torque.

Harvard researcher Neil Roach analyzed the biomechanics of collegiate baseball players’ throwing motion in order to better understand the evolution of throwing. His findings, presented in Nature, suggest that unique adaptations in the arm allow throwers to store and release elastic energy in the shoulder in a slingshot-like fashion.

That elastic energy, initiated by powerful motions of the hips and trunk and stored in the tendons, ligaments and connective tissue of the muscles, helps to create rotation of the shoulder, the fastest motion the human body produces. And from that rotation, so fast it has to be measured in milliseconds, the 105mph pitch is born.

However, one of those elastic structures is a band of fibrous tissue known as the ulnar collateral ligament or UCL. As the primary support for the elbow during the pitching motion, the ligament is put under tremendous force as velocity increases and can ultimately fail or tear, a result that requires the now famous Tommy John procedure to reconstruct the ligament.

“We are at the maximum limit of velocity because we are at the limit of what the UCL ligament can handle,” says Fleisig. “There has been an increased clustering of pitchers throwing at the top level of velocity, but peak velocity has plateaued.”

Since science can’t manipulate the elbow of a pitcher to failure during testing in a biomechanics lab, Fleisig’s research on the upper limits of velocity comes from dead bodies. “The amount of torque required to throw the velocities we are seeing now is right at the limit a cadaver can take,” Fleisig stated. He does note that the cadaver ligaments used in the lab aren’t as hearty as those in 25-year old professional athletes, likely the reason that every pitcher that throws near 105mph doesn’t immediately blow out his elbow.

“I think there are physiological limits to performance,” agrees Roach. “In throwing athletes this is the capacity of the shoulder muscles and ligaments to withstand immense and repeated forces that are essentially trying to tear the arm from the body.”

“Teams have fallen in love with velocity since radar gun speed is one piece that translates to the next level,” said Fleisig, “and it’s something that they’re overemphasizing now.” Because of that, pitchers are going all in for big numbers on the radar gun. But velocity is a fickle mistress, for some the key to a successful professional career, for others, a gift that is lost to injury, squandered by throwing too hard for too often.

As far as whether velocity can still evolve, it is certainly possible, but unlikely. “We don’t throw to kill game for food anymore, we do so in the context of sport,” says Roach. “That doesn’t necessarily translate into more children (the only real metric that evolution can act upon). In short, so far it seems that our throwing abilities may have been important in our evolutionary past, not necessarily in our evolutionary future.”

So, for pitchers, if evolution can’t shape arms to throw any faster, they should concentrate on another essential attribute: the ability to stay healthy as they deliver those 100mph fastballs.

