TEMPE, Ariz. — It was only 1 p.m., less than halfway into Nolan Schanuel’s day-long, self-inflicted punishment. And he was already in excruciating pain.

The exercise regimen that the Los Angeles Angels rookie first baseman conducted over the offseason was not recommended to him by a fitness professional. It’s not grounded in any conventional wisdom. And to pretty much everyone in his orbit, it seemed downright ridiculous.

Schanuel spent two days a week this offseason standing. For the entire day. From the moment he woke up until the moment he went to bed. His only reprieve was for meals.

It was a routine that sounds far easier in theory than it is in actual practice. And one that required a great deal of mental and physical willpower to complete.

“The first time, I was losing my mind,” Schanuel said. “The first day it was 1 p.m. and I had lost my mind.”

“I made it,” he noted. “I don’t let myself fail. I can’t.”

Schanuel turned 22 years old on Wednesday. The Angels shocked the baseball universe last August when they promoted him to the Major Leagues just one month after drafting him in the first round. This time last year, Schanuel had yet to start his final collegiate season at Florida Atlantic. But after posting a .402 OBP in 132 plate appearances, he’s set to be the Angels’ everyday first baseman in 2024. And therein lies the purpose behind his unique test of endurance.

Schanuel still has many things to prove at the game’s highest level. Chief among them is an ability to post — to sustain a 162-game season despite coming off a far more truncated collegiate schedule. He played just 29 major-league games last year and acknowledged his legs would start to feel tired in the later innings. The more back-to-back days he played, the earlier that fatigue would creep in. The heavier his lower body started to feel.

Schanuel didn’t start this exercise to torture himself. He did it to ready himself, fitting for a player whose entire on-field persona is about self-discipline.

“We have a lot of hope for him and he has a lot of hope for himself,” said Angels manager Ron Washington. I like his work ethic, and with that, all you can do is get better.”

When people think of great endurance tests, they tend to think of marathons or triathlons. Standing is something most people do passively. But Schanuel soon found how to make it an exercise.

His days would be filled with activities aimed at passing the time. He’d run errands or do baseball activities. He’d even walk to the gym — no driving was allowed, of course — where he’d do full-body workouts, including leg drills.

“At 5 p.m. is when I would feel mentally drained, physically drained. That’s when I had to fight the most demons. From 5 p.m. to 10 p.m., or whenever I was getting ready for bed. It was just the hardest time.”

His favorite evening activity during those days was mini golf, with his friends or with his girlfriend. It served as a brief mental reprieve from what he was feeling. And, from time to time, some of his buddies would attempt the lengthy exercise with him in a show of solidarity.

He wouldn’t allow himself to crouch at any point, or lift his legs up with his hands to relieve the significant build-up of lactic acid.

“My family didn’t know about it,” Schanuel said. “A couple people were kind of shocked by it. But that’s just how I am. At school I would do some outlandish drills.”

And those confused by his regimen aren’t limited to those closest to him.

“It is (crazy),” said teammate Ben Joyce. “It’s interesting. I’ve honestly never heard of it. But if it works for him.”

“There’s a lot of methods,” said head Angels strength and conditioning coach Dylan Cintula, when asked about Schanuel’s exercise. “As long as he gets the results we need.”

The comment was more tongue-in-cheek. Cintula seemingly wanted to give a diplomatic answer to a question about an exercise foreign even to his expertise. Nonetheless, Cintula was unambiguous that Schanuel had reported to camp in improved shape.

While many health and exercise professionals trumpet the benefits of staying on one’s feet over sitting for long periods — standing desks and treadmill desks have become popular options both in home offices and at workplaces — standing all the time is not generally considered a popular or effective exercise routine. Most online guides regarding extended standing discuss how to mitigate its negative effects: doing deep squats, various stretches and taking breaks to minimize leg, hip and knee stress and pain, plus movement and massage to avoid the buildup of blood that can cause varicose veins.

When Schanuel was much younger, he’d get emotional when he made outs. He’d throw gear, and sometimes break down in tears. The disappointment of failure manifested itself in destructive ways.

He credits his father, Ryan Schanuel, for helping to channel his frustration. Focus it on competing, not complaining. It’s a personality trait he’s still working on.

Now, that passion is seen in how he punishes himself. When he takes batting practice, he’ll automatically leave the box if he believes he swung at a pitch out of the zone. No one forces him, except himself.

The same can be said for standing for a full day. No one would punish him for pulling up a chair, taking a nap on his bed or watching a TV show on his couch. But he would know, and that’s what matters.

Schanuel is so young, and his future in this game appears bright. He’ll enter this season trying to extend an on-base streak that started the night of his MLB debut. More importantly, he’ll try and be an everyday player.

One that can stand at first base for nine innings every night, for nearly 162 nights a season. Without getting tired.

“I feel like my legs have gotten bigger from it,” Schanuel said. “Doing leg workouts, I feel stronger. I feel more enduring. I can do more throughout the day. I feel so much better on my feet than I was last season.

“If you stand throughout the day, it can’t be a bad thing.”

(Top photo of Nolan Schanuel: Matt Slocum / Associated Press)