Diving into New Year's resolutions to get fit or lose weight may be hazardous to your health.
"Consult your doctor before beginning a new exercise program" is a common disclaimer on gym sign-up sheets and workout equipment manuals, and one more people could stand to follow.
Doctors and physical therapists say they often see patients during the early part of the year with injuries—some of them serious—stemming from New Year's resolutions. Not only can such injuries lead to expensive medical bills, they may also waste cash shelled out for fitness gear and gym memberships.
"People tend to get super excited when they make their resolutions," said Dr. Derek Ochiai, an orthopedic surgeon in Arlington, Va. "But going from zero to 60 in a workout regimen can set you up for a lot of problems."
Injuries from exercise and exercise equipment sent 459,978 people to the emergency room in 2012, up 12 percent from 2011, according to the Consumer Product Safety Commission.
Of those, 31,844 required hospitalization, up 34 percent from the prior year. And that's just a small slice of exercise-related injuries—many more consumers end up at their doctor's office rather than the emergency room.
Erin W. was off to a good start on her resolution to regularly work out in her Washington, D.C., condo's gym, visiting almost daily for a session on the elliptical machine. "Being clinically obese and out of shape meant I wasn't as conscious of my form as I should have been," said Erin, who asked that her last name be withheld for privacy.
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By February, Erin noticed a side effect of her workouts. "There was this visible muscle twitch in my knee," she said. "It wasn't particularly painful, but it was annoying."
Her primary care physician suspected knee strain and recommended Erin refrain from exercising for a few months until the twitch subsided. "Not the result I had wanted," Erin said.
Sprains, joint inflammation and other overuse injuries are among the most common maladies doctors see among resolution-makers.
It's usually one of the 'itises,' like tendonitis or bursitis," said physical therapist Tom DiAngelis, director of operations at OrthoSport Physical Therapy in Lynwood, Wash. Both are caused by repetitive activities that aggravate joints. In people who haven't previously been active, the trigger could be anything from too-lengthy runs to overhead lifts of too-heavy weights, he said.
Usually, the problem is compounded by people who take the phrase "no pain, no gain" literally. "Human nature is to think, work through it and it'll go away," said DiAngelis. But doing so can lead to complications and chronic conditions that take more than a few weeks' rest to treat.
Of course, there are also one-time accidents, like someone who takes a header off the treadmill, trips during a boot camp sprint or tumbles attempting a DVD exercise routine. "They can have injuries where they slip, fall and tear some cartilage in their knee," said Ochiai.
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Resolution-makers age 40 and older might even be at risk for a heart attack. "At low-exercise frequency, the 'weekend warrior,' for example, the risk of exercise triggering a heart attack is multiples higher than in people who exercise regularly," said Dr. Micah Eimer, cardiology and medical director for Northwestern Medicine Glenview Outpatient Center in Glenview, Ill.
Doctors say the best course to avoid injury is to ease, rather than dive, into new exercise routines, working your way up to longer distances, heavier weights or more advanced classes. Other tricks to avoid sidelining resolutions:
Vary exercise
If you're exercising multiple times a week, switch up activities, said DiAngelis. "Our body needs rest and muscles in different areas need rest from different activities," he said. That lessens the risk of overuse injury—and it's also what makes you stronger in the long run.
Warm up
It readies your muscles for a tougher workout, said physical therapist Joe Millen. who is also a personal trainer, owns Impact Health in Palm Harbor, Fla. Warming up might entail a general low-level activity such as walking or stretching, or a slower, more controlled take on whatever exercise they plan to do.
Asking for help
"Get a trainer to help you, or even just some advice from a gym employee on how to properly use the equipment," said Dr. Shari Liberman, an orthopedic surgeon at Houston Methodist Hospital in Texas. Bad posture or form while exercising can up the risk of injury, she said, as can using equipment set up for someone of a different height.
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Inventory aches
Assess your health issues before starting a new routine. If you have known health issues, that's when it's smart to seek your doctor's advice first on what might be a reasonable activity, said Ochiai. But doing so can also help you decipher what feels worse, rather than better, post workout.
Read your body
After a tough workout, it's common (and normal) to feel muscle soreness within 48 hours, said Millen. Feeling pain sooner, or in the joint rather than muscles, is a sign that something isn't right, he said.
Liberman said the acronym RICE—rest, ice, compression and elevation—is a good rule to follow in that case. "If it doesn't get better in a few days, then I would go see your doctor," she said.
—By CNBC's Kelli B. Grant. Follow her on Twitter @Kelligrant and on Google.