NEW YORK: To stick to that New Year's resolution to get fit in 2013, experts advise, find a workout that is challenging but doable.

Donna Cyrus, senior vice president of programming for Crunch, the national chain of fitness centers, said January is when too many people over commit.

“People say 'I'm going to go to gym every day. Then they can't achieve that. Their muscles feel like they're dying, and when they stop, they stop,” she said. “We know it happens in about two weeks.”

Instead, Cyrus said, pick just three classes a week and commit to that for a month; then work your way to four.

“Get yourself a realistic goal,” she said.

But realistic does not mean mind-numbing.

Challenge is essential, according to Gregory Chertok, sports psychology consultant. That is why adults prefer difficult crosswords over children's jigsaws.

“Activities that are not challenging are not sustainable” he explained. “The attention of even the seemingly laziest of people is sustained when engaged in challenging activities.”

People tend to set lofty goals without planning for the inevitable obstacles, he added.

“Many hopeful exercisers I've spoken with will set goals beyond their physical and emotional capabilities,” he said. With the New Year comes this new-found dedication but you are who you are. People don't plan for laziness or fatigue or predict their desire for junk food.”

To navigate the ups and downs, Chertok suggests making a list of the tangible, immediate benefits of your workout, from the afterglow of accomplishment to the reassuringly sore muscles, as well as whatever goals you covet in the long term.

“Oftentimes just having visual evidence of the impact of your workout can give you a powerful feeling,” he said.

To keep body and mind guessing, Chertok suggests switching up your routine every two months or so.

“Life requires a bit of change to keep one's interest peaked,” he explained.

Jessica Smith, instructor and co-author of “The Thin in 10 Weight-Loss Plan” book believes success lies not in the grand gesture, but in the baby steps taken every day.

“Break your resolution down into small bite-sized steps,” she said. “One of the main reasons most people give up on their resolution is that it's too overwhelming to make a major change.”

Adding 10 minutes of activity to your day may not sound like much, she said, but small, simple changes have more of a lasting impact than big ones that aren't manageable in the long run.

Tamal Dodge, a yoga instructor and creator of the “Element: Intro to Yoga” DVD, agrees the best way to stay committed is to not go overboard.

“Try not to commit to a total life style change overnight,” he said. “This leads to burn out.”

Instead, he said, make a smaller resolution, such as to work out for 30 minutes three times a week, and make that non-negotiable.

“If you can fit in more, that's great,” he said.

Pilates instructor Lara Hudson proposes pegging that New Year's resolution to Valentine's Day.

“Valentine's Day is the perfect date to focus on reaching your New Year's goal,” said Hudson, creator of the “10 Minute Solution: Tighten & Tone Pilates” DVD. “It's almost exactly six weeks. You can achieve a lot in that time if you put your mind to it.”

To keep yourself accountable, Fitness Magazine Senior Fitness Editor Jenna Autuori-Dedic advises booking your workouts with a friend.

Not only does fitness become an appointment, she said, but going with a friend makes it easy to try new things. And while fitness clothes don't make the workout, Autuori-Dedic said taking advantage of the plethora of outfit choices available today can lift the exercising spirit.

“When I started working out, I wore boys' boxer shorts,” she said. “If you've gotten Christmas money, invest some in workout apparel.”

You're more likely to go to exercise, she notes, if you feel you look good.