A wickedly fast fastball isn’t the anomaly it once was. A decade ago, Major League pitchers threw a grand total of just 196 triple-digit fastballs in a single season. Last year, 40 pitchers collectively threw 1,017.

But while baseball’s hallmark pitch has increased in popularity, it hasn’t increased in velocity.

Consider the confusion over the game’s fastest fastball ever. On paper, the honor goes to Yankees relief pitcher Aroldis Chapman, who clocked 105.1 miles per hour in 2010. But the record could have been set all the way back in 1974. Back then, Nolan Ryan was the first MLB pitcher to be tracked by radar during a game—and while his heater topped out at 100.8 miles per hour, the radar measured Ryan’s ball just before it crossed the plate. Had it eyed the pitch as it was leaving Ryan’s hand (as Chapman’s was), experts believe it might have registered at upwards of 108 miles per hour.

Similar retroactive estimates have put Cleveland Indians pitcher Bob Feller’s fastest fastball at 107.6 miles per hour—and that was all the way back in 1946. Walter Johnson, who played from 1907 to 1927, is also thought to have thrown pitches at 100 mph or more. All of which is to say: Pitchers have been throwing north of 100-mph for the past 100 years. Over the same time period, advances in training, technology, nutrition, and, yes, drugs, have fueled a dramatic upward trend in world-record athletic performances, from the marathon to the long jump to the 50 meter freestyle. But when it comes to hurling a five-ounce, leather-wrapped sphere as fast as possible, humans appear to have plateaued.

“I don’t see it going much higher,” says biomedical engineer Glenn Fleisig, research director of the American Sports Medicine Institute and an expert in the biomechanics of pitching. “I'm sorry to say that, but I don’t see it happening. Baseball isn’t like other sports, where we see people running faster or swimming harder or whatever, where today’s records are smashing the records from 10 years ago.”

That hasn’t prevented pitchers from pursuing the triple-digit barrier at the expense of their arms. A significant number of them undergo major medical procedures to correct injuries from competition. Like the “Tommy John” surgery: When the tendon in a pitcher’s elbow tears, surgeons can replace it with a fresh one from the player’s wrist, forearm, hamstring, or even their toe. Swapping in the relief tendon involves the surgeon drilling holes in the ulna and humerus bones and threading them in a figure-8 pattern with the healthy tissue.

A 2012 survey found that a quarter of Major League pitchers had undergone the Tommy John surgery at some point in their careers. And as the popularity of the fastball has increased, so has the surgery.

Fleisig thinks the rise in Tommy John surgeries has to do with the immense strain that hurling baseballs puts on a pitcher’s arm. By studying cadavers, he and his colleagues found that the force required to tear elbow ligaments is roughly the same as what a pitcher asks of his arm throwing at top speed. When the arm flings back, the shoulder ligaments experience about 100 Newton meters of torque. When it flings forward, the elbow ligaments suffer the same. “It’s the equivalent, at each point, of holding five 12-pound bowling balls,” Fleisig says. “So imagine I hang 60 pounds from your hand. That’s what it would feel like on your elbow or shoulder.” At those forces, he says, pitchers are effectively throwing their arms off. The odds of them throwing much faster seem pretty slim.