My friend Andy has always been a good athlete. He loves running, skiing, and tennis — and he does them all well. He was also extremely lucky, rarely getting injured.

In the spring of 2020, Andy’s luck turned. Both elbows swelled up and became painful. The diagnosis was “Zoom elbow” — an irritation from leaning on the desk during all those remote meetings. It was a strange way to get hurt, sitting at your desk. At least it didn’t keep him from running in the woods. He spent the spring and summer exploring the trails that wound around the kettle ponds in the Seashore.

He stuck to running that fall and winter, since there was not much happening with skiing and tennis because of Covid. The next spring, he started looking forward to road race season. He had always been able to pick up the pace quickly. He started interval training using an app on his phone. He was doing multiple all-out sprints whenever he ran. Suddenly one of his Achilles tendons started hurting and swelling. He dropped the speedwork.

That summer his leg started to hurt when he was sitting — or was it his knee? The pain was hard to localize. Maybe he was limping because of the Achilles? He ran a couple of races, but he wasn’t feeling great. In August, a week after a tough 5-miler, his right knee blew up like a balloon. A 60-year-old runner with a sore knee: that sounded like a sports injury. The doctor drained the knee and gave him cortisone.

The treatment helped a little, but he had to stop running. In fact, it was getting hard to walk. Then the other knee blew up. Things went on like this for a while: X-rays, hassles with the insurance company, a referral to a specialist. He missed the physical and mental aspects of running. He had always relied on running to help him clear his head and manage anxiety. It gave him energy.

When summer faded to fall, he saw an orthopedist who looked at the images and at his history and determined Andy’s problems weren’t orthopedic after all — they seemed systemic. He talked about autoimmune diseases like lupus or rheumatoid arthritis, drained the fluid from Andy’s knees, and sent it off to be checked. The wait seemed long.

Finally, the results came back: it was Lyme disease. Andy was surprised because he’d never seen a tick bite or had the classic bullseye rash nor the flu-like symptoms associated with Lyme.

He’d probably had it for a while, his doctor said. He started the antibiotics and hoped for the best. While most people do well, an estimated 5 to 20 percent of patients who get Lyme have chronic symptoms even after treatment. It doesn’t help when the disease goes untreated for a long time, either.

Andy started to feel better within weeks of beginning treatment. He could walk to work again. That was nice. The days got shorter and colder, and he started to jog again, very gingerly. You could see this wasn’t his old pace. There was some fear there — sometimes you worry that you’re getting too old to do what you used to do, he said.

It wasn’t easy, starting from scratch. Andy got winded after a short distance, even running at what he felt was a snail’s pace. But it got easier. He could go a bit farther, a little faster. The trees bloomed, and he started thinking about racing season again. He hadn’t lost his competitive streak.

This time, he wanted to do it right. He worked with a trainer to develop a strength routine to safeguard against further injury. He began speed work gradually, carefully. He learned about the science behind intervals, tempo runs, and long runs.

He entered a 5K in the city and did well. Modestly, he said it was just a small race, not many people there, not a big deal.

Andy’s race was the Wellfleet Road Race, the hilly, steamy 5-miler in early July. That was the one that mattered. He set his sights on a time of 41 minutes, the kind of time he could run before all of this.

I went to watch the race. When the horn sounded, he put his head down and took off with the pack. I waited and watched the clock with Julie, his wife. We saw him running to the finish line, arms in the air, face lit up. The clock said 40:35. He brought home his first Wellfleet prize, too, a second-place finish in his age group.

Andy knows he was lucky to respond so well to treatment. He has some advice, too, for anyone coming back after a tough diagnosis: start slowly and do what you can, give yourself a break, and rest often while you recover. His new watchwords are “be grateful and be careful.”