WEST PALM BEACH, Fla. -- Jon Lester thought his body was simply slowing down. At 37 years old, he had thrown more than 2,700 innings over the last 15 seasons, including deep playoff runs and three World Series championships. At some point, he figured, it would catch up to him.

But this kind of sluggishness seemed different than just excessive mileage. When Lester would take the mound in late innings, at times he felt like he “hit a brick wall.” He also noticed an increase in sweating, and he was getting dehydrated from the depletion of electrolytes. Lester began wondering if pushing himself to do extra cardio or strength training would help, but his desire to work out -- which he enjoys doing -- had waned.

“I think you just think, 'I'm just not in shape. I'm not prepared to pitch,'” Lester said on Wednesday. “And that's a hard pill for me to swallow. That's what led me to start asking these questions.”

Lester said the lack of energy “is something that’s been going on for a while,” and it became frustrating over the past year -- last season, he went 3-3 with a 5.16 ERA. Lester had monitored his blood work while on the Cubs, and he began doing more research, eventually getting connected with an endocrinologist in New York. One step was determining whether the issue was a hereditary condition that could be resolved with medicine.

After undergoing CT scans and tests, a plan of action was reached last Tuesday night: a parathyroidectomy (removal of a parathyroid gland) to alleviate hyperparathyroidism.

On Wednesday, Lester traveled north for the hour-long procedure that took place on Friday. He wanted to address this ahead of Spring Training -- his first camp with the Nats after signing a one-year deal in January -- but it was delayed because of COVID-19.

“It’s such a minor thing that I didn’t mind getting it done right now and being able to bounce back quickly,” Lester said. “Already less than a week [later], I feel a lot better just energy-wise. … I think that’s the main goal: To feel better physically. And now I’ve got the peace of mind that this thing is done.”

Fifteen years ago, Lester was diagnosed with anaplastic large-cell lymphoma, a form of non-Hodgkin's lymphoma, during his rookie season in Boston. He underwent chemotherapy and returned 11 months later. The diagnosis from 2006 didn’t weigh on him during this procedure.

“The cancer stuff, no, thank God that that stuff hasn’t really crossed my mind for a long time,” Lester said.

Lester returned to Nationals camp on Monday, and manager Dave Martinez said the team is not putting a timeline on his Spring Training debut. Lester already had thrown two batting practices, and he is working on exercises for strength and flexibility in his neck. Since he is tabbed as the fourth starter in the rotation, he has a few extra days to get ready beyond the April 1 opener.

“I think really the big thing is just the incision on my neck and making sure that thing doesn't pop open or anything like that,” Lester said. “But as far as my arm and body, I feel like I can ramp right back up and be right there. I may be a tick behind, but I think we can kind of catch up on the backside of that rotation.”

In an ideal situation, Lester would have stayed on track and completed camp without any delays. He felt, though, that undergoing this procedure was important for both his health and ability to help the Nationals win. Taking a pause from baseball wasn’t easy, but in the long run, it was a decision Lester is glad he made.

“I think a lot of times with athletes, and I’m guilty of it even with the surgery, I don’t do research on things,” Lester said. “The big thing I would relay to people is: Do the research and learn about your body and learn more why levels of certain [things] are going up or going down.”