Of all the numbers that infest baseball, of all those that stand alone or in combination to quantify humans at play, 40-40 is a particularly tricky one.

Forty-forty, as in 40 home runs and 40 stolen bases in a single season, just isn’t supposed to happen.

“Normally, home run guys aren’t fast. And fast guys aren’t home run guys. That’s what it boils down to,” Braves hitting coach Kevin Seitzer said. Pretty simple. It’s a matter physiology and physics. And fairness, too, because no one guy should get all the gifts.

There has been a recognizable version of this Major League Baseball thing since Teddy Roosevelt was in office. And only four players in all that time have piled that much power upon that much speed. And none of them – Barry Bonds, Jose Canseco, Alex Rodriguez and Alfonso Soriano – have been invited to join the Hall of Fame because of suspicions that their deeds were drug-aided. Everything is tainted, regardless of what point in their careers they went 40-40.

And now a 21-year-old Braves outfielder of quite normal dimensions – all 6-foot, 180 pounds of him, dare we say approximately the same dimensions as Henry Aaron – is threatening to bring a younger, more wholesome look to the 40-40 club.

There is only one way to describe what Ronald Acuna is up to now.

“His year is just going to be stupid with what he’s accomplished,” manager Brian Snitker said. Yes, stupid numbers, even now that the youngster is in the grips of a slump.

On Thursday against Philly, Acuna bagged his 40th home run, taking care of the first half of the goal. He became the second-youngest player ever to reach that number, just behind Mel Ott and ahead of Eddie Mathews.

“It means a lot to be compared to superstars at such a young age. Wow. It’s a motivator as well, to continue working,” Acuna said afterward through an interpreter.

He has 37 stolen bases. There are eight games left in the season to round that up to 40.

There is an obvious weight to chasing this kind of history. The air up here is thin. And 40-40 clearly weighs in at 800 pounds.

Acuna has had a pretty miserable last month, hitting under .200 with 40 strikeouts in his past 25 starts. In his role as amateur shrink, Seitzer saw his young charge get distracted and detoured the closer he got to the milestone. And this is a player who for two years seemed so happily unaffected by the hype around him.

“It’s human nature to press a little bit,” Seitzer said. “I felt a couple weeks ago he was over-swinging more. I felt like he was really pushing trying to get to 40 (homers) and I felt like he was getting too big (with his swing). The last week and a half, I like where his swings are. He’s still striking out a lot. He tends to guess too much with two strikes and that’s where he can get locked up – taking called thirds or chasing bad pitches out of the zone instead of just staying with his normal approach.”

Thursday was just his fifth home run since Aug. 16, but for his part, Acuna would admit to no great weight lifted. That’s consistently his way.

“No, I never really focus on that kind of stuff. I never felt any pressure to get there. As I’ve mentioned before, if I hit that home run great. If I didn’t hit it, I didn’t hit it. If I steal the bases, I steal them. If I don’t, I don’t.”

One way or another the Braves and Acuna surely will be relieved when the historic chase is done and the playoff chase takes over.

However the numbers shake out at the end, the combination of talents that Acuna is bringing to the ballpark is unique to this franchise. Other Braves in the past have been in the neighborhood – Aaron 44-31 in 1963 (Milwaukee), Dale Murphy 36-30 in 1983, Ron Gant 32-34 in 1991. But none have gotten so tantalizingly close to 40-40 as Acuna.

“My speed was not that of a base-stealer,” Murphy said. “I just took the opportunity when it presented itself. His stolen-base opportunities will always be available to him because he has more speed.”

You ask the two coaches in charge of the Braves’ hitting and base-running – Seitzer and Eric Young respectively, both long-time players and coaches – and they’ve never seen anything quite like Acuna’s skill package.

And in Kansas City, Seitzer played with one of the all-time freakish athletes, Bo Jackson. “His on-base percentage wasn’t high enough to go steal 40 bases. The power was there. Bo was so raw because of how so little baseball he had played over his life,” Seitzer said. In his best season, Jackson went 32-26.

You ask Acuna’s manager, and he’ll bring up another quality sure to warm the heart of anyone in that position. “Guys got to play a lot to do that. He’s got to post every day in order to allow himself the chance to put up those numbers,” Snitker said.

A quick inventory of the tools Acuna brings to this task:

The Power.

The immediate question is just how does Acuna, with his build, generate such power in surplus? Home run No. 40 on Thursday scraped no wall, traveling 432 feet. And the guy is hardly hulking.

“His legs, his lower half,” Seitzer says. But there’s more.

“What’s even more explosive is his hands. He’s just an extremely gifted kid.”

“The thing that people don’t realize, OK, he’s been struggling a little bit for a while. He’s 21. He’s put up numbers that guys with 10 or 15 years in the big leagues would kill for. And he’s 21,” Seitzer added for good measure. Translation: That power isn’t going anywhere for a good long time.

The Speed.

Being fast is a good start on being an adept base-stealer. It’s kind of a fundamental. But how you employ the speed, that’s the key, Young said.

“Most important to me is the maturity and growth (Acuna) has shown on the base paths,” he said. “He knows right away now when he gets a good jump and when he doesn’t.

“Last year he ran a lot on his own – I taught him a few things. This year I went more into technique. Everyone in the park knows he’s going to run, so he’s been trying to fine tune his technique and his jumps and not just rely on his speed. There have been instances when he said I got in (safely) but I didn’t feel good on my jump. Then we’ll go look at it.”

The modern game is so much about launch angle and exit velocity and not so much about foot-speed. Here is the one player still capable of giving both those disparate measurements a workout. And doing it more than anyone else around, and that includes Mike Trout (his 30-49 in 2012 was the closest he has come to 40-40).

Getting those last three stolen bases, “would mean a lot” Acuna said Thursday.

“To think that only four other players have achieved that. Think of all the people who have played in the big leagues over the years. It would be amazing, wonderful,” he said.

As Braves past and present put into perspective what Acuna is chasing here, the message also comes through that this will not a one-time-only fascination.

“If you’re not amazed you got to take a step back and realize how amazing it is. It’s really hard to do this, and he’s doing it at 21 years old,” first-baseman Freddie Freeman said. “I don’t think this is going to be his only season of 40-40. He’s going to be flirting with this for a long time.”

“He’s going to be able to knock on the door of doing this more often than anyone in the history of the game,” Murphy concluded.