It sounds like an air piston when Alex Len breathes, gasping in sync with the tennis balls being fired at his face. He snatches them quickly and ferociously, exhaling with metronomic rhythm, the sharp pfffs echoing inside this cavernous auxiliary gym on a humid May morning at the University of Maryland.

Len appears almost regal seated upon the stack of red gym mats. Four trainers and team managers surround him on the perimeter. A fifth stabilizes Len from behind. Stiffening his back, Len throws his hands into the air, ready to catch. Initially, it looks like he is surrendering.

Except this isn’t a surrender. The challenge, after all, has just begun. Since declaring for the NBA draft in mid-April after two seasons with the Terrapins, Len has surrounded himself with a trusted crew, each member tasked with arming the 19-year-old Ukrainian for the next battle.

A third ball gets added to the drill, a blue one no bigger than a softball. He’s getting in a rhythm now. Five in a row. Six in a row. Now a fourth ball, purple and heavier than the rest. It’s constant commotion, but the 7-foot-1 center looks almost peaceful.

It’s almost enough to forget about the silver walking boot strapped around his left foot.

Len had surgery to repair a partial stress fracture in his left ankle on April 27 at Mercy Hospital in Charlotte. He walks with crutches but hops the stairs two at a time. The foot’s range of motion has improved, but it still hurts when trainers grab the heel, arch back his toes and apply pressure to stretch it out.

Stress fractures worsen over time, compounded by overuse, so it’s impossible to pinpoint exactly when the injury occurred. Maybe during the ACC tournament in mid-March, when Len says he struggled to walk around the team hotel after games. Maybe against Iowa in the National Invitation Tournament semifinals April 2, when the pain reached its peak. Right now, though, the origins don’t matter so much.

“What it did show me was that he’s a tough kid, a very tough kid who played through it, played through pain, which eventually became an injury,” Maryland Coach Mark Turgeon said. “I think Alex was just trying to win as many games as he could down the stretch and be successful. Never one time did the kid come to me and say he had a really bad injury.”

Once Len decided on surgery, he traveled to North Carolina to see Robert Anderson, a foot and ankle surgeon who has operated on several NBA stars, including Kyrie Irving and Stephen Curry. Len wants NBA teams to be reassured when evaluating his health, and there’s no one more trusted under these circumstances than Anderson.

It was the first major surgery of Len’s life, and his body reacted poorly to the anesthesia, which induced nausea and vomiting. He also doesn’t quite remember posing for a pre-operation photo snapped by his agent, forming a circle with his thumb and pointer finger around his eye, a monocle in full hospital gown.

‘Where we need to be’

Len thrives on structure and familiarity. His current daily workout routine was choreographed by Turgeon and Maryland director of basketball performance Kyle Tarp, the same duo responsible for overseeing Len’s 35-pound weight gain last offseason.

It’s why he signed with agent Michael Lelchitski, a Russian who has become close with Len’s family. It’s why his iPhone buzzes for every meal, why an app tracks his sleep schedule and why he saves grocery receipts for Tarp’s inspection and approval.

Individual workouts for NBA teams were expected to boost Len’s stock, playing up his strengths as a tireless worker with an attractive skill set. But because of the injury, Tarp has been forced to get creative. “We’re going to come back stronger,” he said. “We’re going to come back better. And he knows that.”

Len begins his workout flat on his back in Maryland’s basketball performance center. His eyes are closed during this visualization exercise. He pictures his favorite low-post moves. Up-and-unders and dribble-drives. Something Tarp calls “the Tim Duncan,” a shoulder-to-shoulder sweep in which Len arcs the basketball over his head, or “the Kevin Durant,” in which the ball moves linearly, sharply across the chest.

Tarp bets big on the mind’s power.

“The ankle is the least of our concern,” he says. “We need to make sure the rest of the system stays where we need to be.”

‘Alex is a worker’

After several sets of seated medicine ball slams, pull-ups from a prone position and exercises involving a weighted bean bag to strengthen his grip, the workout moves to the gym upstairs. Len won’t shoot today, but on days that he does, they lower the backboard to simulate to the normal distance between his shoulders and the rim so the transition will go smoother once he can stand.

For now, Len is perched atop the stacked mats and fielding chest passes. Behind him, a student manager slaps his shoulders, offering token resistance. Len’s legs occasionally kick forward when the passes arrive, as if he just wants to say boot-be-damned and return to midseason form. But the recovery process takes patience. It takes restraint.

Every drill is designed to cure a weakness. Twenty minutes of corrective exercises are designed to prevent the body from overcompensating in other areas because of foot immobilization. Len needs ballhandling work, so he palms and pounds basketballs into folding chairs. Sometimes, he counts the number of repetitions out loud to practice communicating in English, a language Len first started studying less than two years ago. When Maryland women’s assistant David Adkins peppers Len’s lower-left quadrant with tennis balls, it’s because a vision training machine showed Len reacted slower in that specific region.

Len’s injury precluded him from working out at the NBA draft combine last month, but he still conducted interviews with most of the lottery teams and came prepared. The binder Len shared with executives contained workout schedules and nutrition plans — anything to show teams that once he reaches the last page of that book, the boot will be gone and he will be himself again.

“That’s Alex,” Turgeon said. “Alex is a worker. Alex has been a pro since he stepped foot on campus. That’s just the way he approaches it. You have to dial him back because it’ll work.”

A little bit of pain

The scar crawls up his leg like a splotchy caterpillar, the raw remains of 12 stitches bisected by the incision mark. Removing the walking boot, Len leans back on a cushioned training table, propping his good leg up onto a towel rack.

Trainer Matt Charvat approaches and works his toes from side to side, bending forward at the ankle and applying slight pressure. Len grips the table edges for balance. It hurts but only a little.

For two years Len has lived with teammate John Auslander, a forward who is one of Len’s best friends. Last year, Auslander dealt with the same partial stress fracture, the specificity of which Len says is relatively uncommon among basketball players. Len ponders this oddity for a moment, wondering about the coincidence.

Yet Len doesn’t appear much burdened by fate or circumstance. He sees the problem and acts, like with the 38 marbles Charvat just dumped onto a white towel. Len must return them to a plastic container using only his left foot. He struggles initially, curling his second toe around the glass and bending the marble into the open space. Several fall. One rolls off the towel. But soon Len hits his stride, completing the task twice before grabbing the black crutches and calling it quits.

Len has been in control all day, each second of the nearly three-hour workout scripted for maximum efficiency and oversight. But there’s something on his mind, an unanswered question he asked Charvat about the next step: June 27, when Len hears his name called at the NBA draft.

“You think I’ll be able to walk on the stage?”