Even a terrific fastball hitter like Buster Posey has a speed limit. Not long ago, the Giants catcher quizzed a few older ballplayers about the recent invasion of flame-throwing heat monsters.

“I’ll ask them. ‘Is it just me?’ I mean, I’m about ready to move the mound back a little bit,” Posey cracked.

“You have middle-relief guys coming in throwing 100 mph. And I’m like, ‘Wait, I thought 100 mph was supposed to be one or two guys across the league.’ “

It’s not just you, Buster. Triple-digit radar gun readings, once the sole provenance of legends like Nolan Ryan, now make for a crowded expressway.

A record 31 big league pitchers touched 100 mph on the radar gun last season, according to PITCHf/x data, and two pitchers — Aroldis Chapman and Mauricio Cabrera — averaged at least 100 mph for the season.

There is more heat in the forecast. Baseball America documented another 71 prospects clocked at 100 mph in the minor leagues last year.

The fastball fixation is nothing new. You can fairly trace pitching history through baseball’s rapidly spinning seams, from Walter Johnson to Bob Feller to Bob Gibson to Nolan Ryan to Aroldis Chapman.

But it’s becoming increasingly clear that baseball’s best arms are cruising at dangerous speeds. Pitchers are getting injured at record rates, and a recent wave of studies demonstrates a relationship between increased velocity and increased risk in Tommy John surgeries.

There are apparently only so many Newton-meters of torque a human elbow can take.

“We’re seeing so many young kids coming up throwing 95-98. They throw as hard as they can for a full season,” A’s catcher Stephen Vogt said, “and they come back the next season and their arm is gone.

“I think it’s become the mentality of a lot of organizations: ‘Well, let’s just use this guy until he can’t pitch anymore and next in line.’ I’m not a big fan of that.”

Velocity has gone up or held steady in 14 of the past 15 seasons. In the bullpen, especially, it’s as if everyone suddenly comes equipped with a Rich Gossage fastball. It’s not just Goose anymore, it’s geese: The top 20 relievers last year averaged 96.72 with their heaters, according to numbers collected from fangraphs.com.

Better training, more sophisticated throwing programs and advances in medicine have paved the way for this generation of young, hard throwers. But there’s no way to strengthen an elbow ligament, leaving the UCL to bear the brunt of this unprecedented fastball force.

Stan Conte, the former Giants and Dodgers trainer, last year was the first to report that while shoulder injuries are on the decline in major league baseball, the number of elbow injuries continues to rise.

The trend of mega-velocity has been described as baseball’s Faustian bargain: Throwing hard will get you drafted and could make you a star — and then, almost certainly, it will destroy you.

“Our bodies are not designed to withstand that kind of velocity,” Vogt said. “If you can, you’re a freak.”

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