The calls started in late March and early April, about two weeks after newly homebound Americans began diving into new workout waters.

A Minnesota grandfather had pumped up the tires on his long-neglected bike and pedaled six miles with his granddaughter’s virtual gym class. His calves hurt so badly he couldn’t walk.

A former NFL safety in Louisiana had taken up running miles instead of yards in shoes that had seen too many seasons. His feet and knees ached.

A working mother in Virginia, suddenly home all day, had followed online videos through scores of dips, pushups and jumping jacks. She developed tendinitis in both shoulders.

For people faced with more free time but fewer athletic options, overuse injuries are the painful flip side to the noble pursuit of “quarantoning” as getting toned during quarantine is known.

Medical professionals and a footwear retailer on the receiving end of those distress calls say eager exercisers often overestimate how much of a new activity their musculoskeletal systems can handle.

And they might do it again when they return to their gyms and studios after weeks or months away, expecting to be at the same level they were in March.

“Unfortunately we’re going to see a large number of people come to us when we all get back to quote ‘normal” again,’ said Michael Ercole, a Virginia physical therapist. “They’re going to get back into the way that they used to do things, and they’re going to get hurt.”

Don't try to go from 0 to 60

Health-care professionals say they are seeing more injuries from bad home-office setups than from bad fitness forays, but physical therapists in particular say they are seeing both — and occasionally some creative person will combine the two.

Kelly Roberts Lane, a physical therapist in Mahtomedi, Minn., said a tech industry executive ended up in her clinic after buying a new walking treadmill desk for his home office. Overnight, he went from long hours of sitting to walking up to 14 miles a day — with a little running thrown in as well.

Before long, he had a strained foot.

Lane, who also fielded the call from the cycling grandpa, said she is hearing from many office workers who wanted to take advantage of the unexpected downtime to get in shape but then went too hard too fast.

“We’re going from sedentary at work to a ton of movement because we can,” Lane said, “and we’re just not conditioned for it yet.”

Shannon McCarty, a learning specialist in South Riding, Va., was a runner before the pandemic, but she injured her left ankle while hiking in March. Then came weeks of staying home.

“Seeing all these people running by my house all the time, the beautiful spring weather and the extra time was making me want to get back out there,” she said.

She started carefully: a one-mile run, then a two-mile run, to test her ankle. All seemed fine, so the next time she ran, she decided to go farther.

“I was feeling good at three, and I kept going and it didn’t even hurt,” she said. “And then I got home and two hours later, my other ankle was the size of a tennis ball.”

She had torn a ligament.

“I didn’t even feel it happen,” she said. “Maybe I just had such a runner’s high from getting out and away from my children. I just ran right through it.”

Don't try to go from apples to oranges

Fitness in one activity often doesn’t translate to fitness in another, even when the activities seem similar.

“The tennis court is closed, so they picked up a mean game of ping-pong,” Lane said of a few patients. “I’ve been fixing shoulders and elbows.”

Ercole, who runs a physical therapy practice in Northern Virginia and got the call from the woman with two tender shoulders, said another patient in her mid-30s showed up with pain in her kneecap.

She’d been very active, especially in spin classes.

“She said, ‘They shut my spin cycle studio down, so when I came home, I decided I was going to go out and start running because I needed some cardio,’ ” Ercole said. “And she couldn’t understand why she could spin-cycle for hours, but she couldn’t run more than a mile.”

She ran, literally, into a common mismatch: Her cardiovascular system could handle running, but her bones, joints and connective tissues weren’t ready for the pounding.

Not surprisingly, a lot of new injuries have to do with running and walking, as they’ve been the only option for many people the past couple of months.

Running can be especially hard on a body that isn’t used to it. The heart and lungs adapt in three to six weeks, Ercole said. But bones, joints, muscles and connective tissue require eight to 12 weeks of buildup before they have the strength needed to support that kind of pounding.

“Running is very catabolic,” he said. “It breaks tissue down because it’s the same motion over and over. And if you don’t have the proper gait, the proper shoes . . . if you haven’t prepared to run, sooner or later you’re going to come in and see us.”

Chris Farley, owner of six Pacers Running stores in the D.C. area, said half of his shoe sales since the lockdown have been to new runners or walkers, and about 20 percent have been to people who called with aches or full-blown injuries.

Their most common complaints are knee or hip problems, shin splints and plantar fasciitis, which causes sharp pain in the arch of the foot or heel.

“We’re not selling a lot of apparel, we’re not selling a lot of socks,” Farley said. “It’s shoes and injury prevention. I would say that’s literally 95 percent of what we’re selling right now.”

Farley said his most memorable recent customer was former Washington Redskins safety Ryan Clark. He hadn’t done much distance running before and quickly developed problems with his feet and knees. He had been running in old shoes that were too broken down to support the new activity.

Don't get so bored that you'll try anything

“I’m bout to be a runner!” Clark tweeted after getting his new shoes. “Gotta find someway to combat these snacks!”

Ercole said a 40-something colleague who works in his practice’s corporate office was sitting on a stool competing in a virtual bike race using a virtual-reality headset. She leaned over too far going around a virtual curve, fell off the stool and sustained a very real shoulder injury.

“That’s how crazy this has gotten,” Ercole said. “People are looking for things to do, and they haven’t done these things, ever. Next thing you know, funny things like that happen.”

Fortunately, not everyone calling a health-care professional about exercise is already hurt.

Matthew Matava, chief of sports medicine and professor of orthopedic surgery and physical therapy at Washington University of St. Louis, said he and the colleagues he spoke with had not heard from a lot of newly injured people, but they were getting a lot of calls from patients who wanted to make major lifestyle changes and didn’t know how to start.

He recommended that sedentary people and those with previous injuries talk to their doctors before beginning an exercise program to make sure they’re starting safely.

“I’ve had several patients who want to use this as a sort of reset of their life,” he said, “to get in shape, to exercise more, to drink less, to eat less, to perhaps stop smoking.”

Liz Joy sees all kinds of people who are starting from scratch in her role as senior medical director for wellness and nutrition overseeing four medical fitness centers in Utah. Her practice helps people with preexisting health problems learn to exercise safely, and she spends most of her time prodding people to move more.

But she also treats people who have eating disorders and use excessive exercise as a coping mechanism, and this stressful time is causing some of them to push too hard.

“We’re kind of seeing both extremes,” Joy said. “There’s a lot of people who are sitting in the chair and eating too much salty sugary snacks and doing nothing. . . . At the other extreme are people who self-medicate with exercise in a way that can be unhealthy.”

Go shorter and slower

The key for anyone who wants to try a new activity, or one they haven’t done for a while, is to start slowly.

“Do something really, really light, like wall slides or situps or just something — whatever you want to do to get you going again,” Matava said. “As you get motivated, you see some results, and you can do a lot more.”

If you want to run, Ercole said, walk first for a couple of weeks, then add in a little running to your walking, then increase the amount of running.

If you want to do more strength work, he said, target several different body parts with one activity each rather than starting a bunch of activities that put all the stress on one. Start with just 15 reps, and build up reps before increasing weight.

“You change one variable at a time,” Lane said. “Say you were interested in trying a new yoga video, a peloton bike, and you want to get your running shoes out. Pick one at a time.”

Also, Lane says, “it’s okay to just walk. Pushups and squats and walking can keep you very conditioned.”

Whatever you do, they all said, don’t quit, even if something goes wrong at first. Back off, and when you feel better, try again, ideally with a bit of guidance — and take it easy.