Jumping on the treadmill or cross trainer for 30 minutes can blow off tension by increasing levels of "soothing" brain chemicals like serotonin, dopamine, and norepinephrine. What's fascinating, though, is that exercise may actually work on a cellular level to reverse stress's toll on our aging process, according to a 2010 study from the University of California—San Francisco. The researchers found that stressed-out women who exercised vigorously for an average of 45 minutes over a three-day period had cells that showed fewer signs of aging compared to women who were stressed and inactive. Working out also helps keep us from ruminating "by altering blood flow to those areas in the brain involved in triggering us to relive these stressful thoughts again and again," says study coauthor Elissa Epel, an associate professor of psychiatry at UCSF.
FIT TIP: To trim your tummy, do fewer crunches and more planks: Begin on all fours, hands under shoulders, knees under hips, then lower forearms to floor and extend legs straight behind you, balancing on toes. Keeping abs engaged and back flat, hold for 30 seconds; do 10 reps three or four times a week. Limit crunches to no more than three sets of 15 at a time. Anything beyond that isn't doing you much good, experts say.