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 centres, said January is when too many people overcommit.
"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 with the American College of Sports Medicine. 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.
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 in Venice, California, 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."