Revamp your routine

"The more you do a particular physical routine, the more your body adapts to it and the less challenging it becomes, so you stop seeing results," Michaels says. In order to keep building new muscle and improving your cardiovascular fitness, give your body new challenges. Research suggests that engaging in a variety of physical activities is also good for your mental health: A study by The Johns Hopkins Bloomberg School of Public Health found that seniors who regularly engaged in a wide variety of physical activities had a significantly lower risk of developing dementia than those who only did one type of activity. Swap a yoga class for an aerobics class, or trade fitness DVDs with a friend so you get new-to-you workouts.

Revitalize your workout with music

According to a 2008 study published in the Journal of Sports & Exercise Psychology, listening to upbeat music can increase endurance by as much as 15 percent and improve positive feelings about working out (meaning you'll be more likely to keep doing it).

Step 5: Get clear on relationships

Reinvigorate old friendships

To renew a connection that's grown stale, Los Angeles–based life coach Julie Zeff suggests bringing something new to the table. "Introduce your old friend to a new side of you by inviting him or her to join you in doing something you love—whether it's watching a movie, participating in a hobby, or reading a particular book." And don't forget the importance of simply sharing what's happening in your life and asking your friend to do the same; it keeps your friendship up to date and let's you focus on what you have in common.

Know when it’s time to move on

If you've tried to improve a relationship and you're still feeling unfulfilled, it may be time to part ways. Although it seems callous, if the relationship is a source of frequent or intense stress, your health may be paying the price: A 2009 study of healthy young women found that those with the most relationship-related stress had the highest concentrations of pro-inflammatory immune cells in their bloodstreams—an indication that they were more susceptible than their peers to the long-term detrimental effects of inflammation (which has been linked to heart disease, diabetes, and cancer).

If you're wondering whether a relationship is worth saving, Louden suggests asking yourself these questions: Do you feel drained after spending time with this person? When you're interacting, does the conversation center on criticisms and complaints? Are your muscles physically tense, or do you experience symptoms such as an upset stomach or headache when you're together? Answering yes to any of these questions means it’s time to move on.