They experiment with their powers, refining their expectations of how high and how far they can jump, how tightly they can make a turn, how close they can get to a hologram without clipping it.

And when that gets boring, they branch out into more daring experiments, including throwing each other past obstacles, which they really shouldn't be able to do.

They occasionally fail to avoid a hologram, but inflict no damage on themselves or the equipment.

An array of monitoring equipment records and analyzes their movement, comparing it to records of Batman, Robin, Flash, and other people who've used this facility. 

They're doing pretty well with the holograms for their first time through, so Flash has the 'enemy' figures start shooting at them: little holographic blips of red to represent bullets, easily dodged if one is a speedster. Cover is provided in the form of more (and more varied) physical obstacles, sliding out of the walls, floor and ceiling.

Green 'civilian' holograms scatter or are mown down to blanket the floor, adding to the challenge.

Impulse is the more creative of the two, with Warp tending to follow his lead. They communicate amazingly well without the use of words, which is useful when they're going too fast for sound to be an effective medium.

They don't come across as veteran superheroes; they're clearly still learning, making new discoveries moment by moment about tactics and their own powers. But they're learning very, very fast.

Well, that'll be useful in the field. He'll have to run some simulations with them at some point, so they can learn to work with a third person. 

...he starts throwing in a few white holograms, moving among the herds of green, to see if they remember what those mean. The 'enemies' switch from focusing on the superheroes to firing at the white figures as well. 

They rearrange the obstacles to provide cover for the white holograms.

Their cover isn't perfect, though. One of the white holograms at the edge of a group of greens is in the path of a bullet and not going to get out of the way in time. Warp, by now moving at speeds that make the bullets seem to crawl, points out the problem to Impulse—

—who sizes up the situation in an instant, then matches velocities with the bullet and very deliberately grabs the intangible red blip out of the air. It vanishes as soon as he touches it, of course, but the intent is clear: if these weren't holograms, he would have saved that person's life, at minimal risk to himself. Then he changes course again and bounces away to stack some more crates.

After a few more variations on such scenarios, all of which the pair deal with pretty well given their inexperience, Flash ends the training session.

"I expect you're hungry after that."

He frowns. "What time did your mother want you back? I'd like to discuss some things I noticed about the way you handled that course."

"She'd rather we were home by seven but won't start worrying until ten."

It's only mid-afternoon. "Plenty of time, then. Let's get some proper food into you before we do anything else." 

He leads the way to the kitchen, which is conveniently nearby, and cooks them a - rather belated - lunch. 

"First of all," he starts during a lull in the cooking process, "I was very impressed by the way you two work together as a unit. But for exactly that reason, I'm worried you might find it difficult to adjust to working with me, since you're so used to each other."

"Yeah. We're quick learners, though. As you may have noticed."

"I did." Flash smiles at them over his shoulder.

"Good job with the white holograms, as well. I know I said I wouldn't include those, but I thought you could do with the added challenge." 

"It was fun!"

The food is done; he chose something that would cook quickly.

After a break to serve it out, Flash brings up the issue of their unexpected strength. He pulls up the video on a screen and plays it back for them - that jump, landing halfway up the wall, the various times they picked each other up and threw. 

"You seem to be able to jump, and throw each other, further and higher than I would expect from your size and apparent physical fitness. That's not a standard effect of the superspeed formula - I mean, I can't do it."

"I thought there might be something odd about that, but it was hard to be sure. Well. Another interesting mystery for the collection, I guess."

"I'm starting to wonder if you weren't already some kind of metahumans," Flash muses.

"Did you notice anything like that before you acquired superspeed?"

"I wouldn't have been nearly as intent on acquiring superspeed if I had!"

Flash chuckles. 

"So it wasn't your first choice, then?" he asks, mock-offended.

"You didn't spend years dreaming of working with your hero, the Flash?" 

He strikes a pose, which would probably look more heroic if he'd bothered to stand up from the table first. 

Impulse cracks up.

"Nope, sorry, it was all about the easily accessible superpowers."

"'Easily'," Warp repeats. "Uh-huh. Four years of work definitely qualifies as 'easy'."

"By comparison to 'I have no idea how to even start', it absolutely does!"

In between jokes, they go through the rest of the training exercise, discussing how the pair handled it and what they could have done better. They managed pretty well, but their inexperience shows. 

"I think we still have time to go another round with me in the mix, if you're recovered from the last one," Flash says when they're done.

"I'll tell the computer to generate a randomized course, same sort of thing as last time, so I won't have any more idea what's coming than you." 

Impulse bounces. "Ooh, yes please."

"Do you have a solution to the problem of communicating at high speeds when you can't wait for sound? We tried learning sign language but it turns out bad sign language is actually less efficient than just knowing each other really really well. Probably should've stuck with it long enough to get good, but we weren't expecting to end up as your sidekicks."

"If we're not actually moving at the time, we can just...talk faster," Flash explains.

"I've practiced that with the previous Flash. Otherwise, there's the method I use with other Leaguers, which is...basically texting? That's better for asynchronous communication, though. Maybe sign language is the way to go."