"When I start exercising, I always stop after a few days. How can I stick with it?"

By now nearly everyone knows it's healthy to exercise at least 30 minutes each day, five days a week. Congratulations if you are one of the 3.5 percent of Americans who get enough exercise! Don't feel badly, though, if you don't get enough physical activity. You may have started an exercise plan before and failed to keep going. If you're ready to try again, here are four simple ways to start and stick to an exercise plan. Make sure to check with your doctor before starting one.

1. Find a good match

Find something that fits your interests and strengths. What do you like doing? Walking, yoga, biking, tennis and dancing are all great ways to exercise that also may make you feel good. Exercise you enjoy today might be different from what you did when you were younger. I used to run track in college. A few years ago I tried to start running again, and my knee swelled and hurt for weeks. Every few weeks I tried to run with the same painful result. Finally I quit, discouraged. It took me years to accept that walking is a fine alternative to running that I can also enjoy.

2. Get strength in numbers

If you get energy from being around others, consider joining a team sport. Many leagues have seniors divisions. Or, try signing up for classes at a fitness center. You might enjoy a spin class to get exercise and to be with friends or to make new ones. If you like doing things by yourself, you can find lots of different exercise options to try at a fitness center and still feel the support of exercising alone but near others.

Summer is a great time to walk on a nature trail or on a quiet street in your neighborhood. In bad or extremely hot and humid weather, you can get in your 10,000 steps a day at a local mall. You can watch TV and march in place, step off and on a platform, or walk on a treadmill. A used treadmill is not that expensive. Often you can find one in like-new condition because the owner stopped using it!

3. Make it fun

No matter how you choose to exercise, getting in your 30 minutes a day is easier when you use a few tricks. You can walk or dance to your favorite music, read a book or magazine while on a stationary bike or treadmill, or just enjoy the beauty of nature to make the time pass more quickly.

Many people stop exercising right when they are about to succeed. Sweating, slightly sore muscles, heavy breathing, an increased heart rate and feeling short of breath are a normal part of exercise. Keep going!

4. Ease into it

The key to starting and sticking to an exercise program is to start low and go slow. "Many sedentary people push beyond their usual range when they try to exercise too quickly or intensely," according to The Wall Street Journal article "Hard Wired to Hate Exercise." Even walking can be too much for someone who's been sedentary for years. You may need to build your confidence and stamina more slowly. Cooking, gardening and housework are activities that can build your tolerance for exercise. You can even break up the recommended 30 minutes of daily exercise into three 10-minute sessions. You'll still benefit from it.

No matter what you do to exercise, be careful not to overdo it. Save the 20-mile charity walk or the extra 18 holes of golf until you've worked up to it.

Published on June 5, 2013; updated on May 5, 2014.

Dr. Robert Herr

Dr. Robert Herr, M.D., M.B.A., practiced internal medicine and emergency medicine for more than 20 years prior to serving as a medical director at Regence. Dr. Herr frequently lectures and writes about health care issues affecting seniors.