But even when we're ready to hit the gym, sometimes family and friends can sabotage our fitness plans.
Melissa Schorr freely admits she'd rather her husband come straight home after work than head to the gym near his office. When he calls from work to say he's going to the club to avoid sitting in evening rush-hour traffic, "I'm never happy to hear it," says Schorr, an author in Seattle.
"That means I have to feed, bathe and put our 1-year-old to sleep all by myself," she says. "What makes it worse - we actually own an elliptical machine that sits down in our basement unused."
It's not that she doesn't want him to work out at all, just not when the timing is bad for her.
"Sometimes I encourage him to come right home and suggest he can work out later," she says, "but often he gets too tired after battling traffic and waiting for dinner and ends up not working out at all."
Family members may contribute to our couch-potato culture more than we might think.
A newly released survey by the International Health, Racquet and Sportsclub Association (IHRSA) in Boston and George Washington University Medical Center in Washington, D.C., explored why people don't go to the gym.
Not surprisingly, the nationwide survey of more than 1,700 people, conducted online last fall, found that many Americans say they don't go to health clubs because they don't have time, they find the gym environment intimidating or memberships cost too much.
But in addition, when people were asked if their spouse or partner thinks they should go to the gym regularly, 48 percent disagreed. When asked if their kids thought they should go, 51 percent disagreed.
Even people who exercise for a living can get pressure to skip a good sweat. Kathy Kaehler, a personal trainer in Los Angeles, says her mother recently told her she should cut back on her workouts, that "doing stairs for cardio is too hard on my system and that I should be careful of my bones."
"Of course I have to go back and explain to her about how strengthening your body is good and will keep you young and healthy," says Kaehler.
But who will cook dinner?
Fitness foes within the family may be an underappreciated factor in why so many Americans don't exercise, says Kathleen Rollauer, IHRSA's senior manager of research.
"A positive social environment helps," she says.
There are a few common reasons why family members or friends may discourage exercise, says Justin Price, a personal trainer in San Diego and spokesperson for the IDEA Health and Fitness Association.
And it's not so much about you - it's about them, according to Price.
"They worry about the disruption in their own life," he says, noting this is especially true for married women whose trip to the gym may mean someone else has to prepare breakfast or dinner, buy milk or pick up kids from after-school activities.
Family members may also fear being compared to the person working out. If only one person in the family is fit, the others may start to feel like a failure, Price says.
His advice for dealing with these issues is to communicate clearly to everyone that the time spent away from them for exercise isn't about getting out of the house or avoiding them; it's about doing something positive for your physical and emotional health.
Schedule it, but be flexible
It also helps to plan your workouts ahead of time and let them know, rather than giving last-minute notice when they may be counting on you to be there for them.
And, of course, be considerate and flexible, taking others' priorities into account, too, says Keli Roberts, a personal trainer and group fitness instructor at Equinox in Pasadena, Calif. "Sometimes you have to compromise," she says.
One of her clients was working out intensely - more than two hours a day, six or seven days a week - until her husband told her to cut back. "He just felt it was taking too much time away from the family," Roberts says. The compromise was for the client to go to the gym three days a week for an hour each time, which is still a respectable amount of activity.
Above all, remember that you won't win over your family by nagging about their poor fitness habits. But you might subtly incorporate fitness into your family life by suggesting active outings, Price says.
Sunday dinner, for example, could become a picnic with a hike beforehand. And playing sports the kids enjoy is a win for everyone.
"Just don't guilt them," he says.