If you have depression or anxiety, you might find your doctor prescribing a regular dose of exercise in addition to medication or talk therapy.

"There's substantial evidence that exercise can enhance mood and reduce symptoms of depression," says Kristin Vickers-Douglas, Ph.D., a psychologist at Mayo Clinic, Rochester, Minn. "It's not a magic bullet, but increasing physical activity is a positive and active strategy to help manage depression."

Exercise has long been touted as a way to maintain physical fitness and stave off high blood pressure, diabetes, obesity and other diseases. A growing volume of research shows that exercise also can help alleviate symptoms of certain mental disorders, such as depression and anxiety, and help prevent a relapse after treatment.

Before you think, "Yeah, right," and move on, consider this: Exercise doesn't have to come in large doses to offer psychological benefits. Even as little as 10 minutes of low-intensity walking helps. Your goal doesn't have to be losing 20 pounds, being able to run five miles nonstop or hitting the gym at 6 a.m. three days a week for a sweat-drenched workout.

Rather, the idea is to do something active in order to trigger the mechanisms that reduce negative moods and improve positive moods. And with a little planning and some practical tips — after all, it's not a matter of sheer willpower — adding exercise to your treatment program won't seem so daunting, even if you experience severe symptoms of depression or anxiety.

Despite ongoing research, just how exercise reduces symptoms isn't clear. There are plenty of theories, though, about both the physiological and psychological pathways that can improve symptoms related to depression and anxiety disorders, including sadness, anxiety, stress, fatigue, anger, self-doubt and hopelessness.

One of the physiological mechanisms that may be at work is an increase in levels of certain mood-enhancing neurotransmitters in the brain. In addition, exercise may boost feel-good endorphins, release tension in muscles, diminish sleep abnormalities, reduce levels of the stress hormone cortisol and even increase body temperature, which has calming effects.

Psychologically, exercise can work in numerous ways, Dr. Vickers-Douglas says. Among them:

• Improved accomplishments and confidence. Engaging in physical activity affords a sense of accomplishment and can provide a boost in self-confidence — you've met a goal or challenge.

  "Having confidence in our ability to make positive change is strongly associated with actually taking steps to make that change happen," Dr. Vickers-Douglas explains. "However, people with depression often feel ineffective in taking care of themselves and their responsibilities. They may lack confidence in their ability to manage themselves and their depression. Achieving physical activity goals, no matter how small, can boost self-confidence and a sense of accomplishment, which makes it easier to take the next positive step."

• Positive distraction. When you have depression or anxiety, it's easy to repeatedly focus your attention on yourself, your symptoms and the consequences of your symptoms — to ruminate. But that kind of dwelling interferes with your ability to problem solve and engage in more active coping strategies. It can also make depression more severe and longer lasting.

  "Physical activity can help shift attention away from unpleasant or unhelpful thoughts and instead direct attention toward neutral or pleasant thoughts and activities," Dr. Vickers-Douglas says. Exercise provides a positive shift in focus — to your surroundings, to the music you listen to, to other people.

• Improved self-esteem. With anxiety and depression, self-esteem can take a hit. Getting exercise, even small amounts, can reshape how you think about your appearance and your own self-worth. Doing something for yourself means granting yourself more value.

• Positive pairings. The physical experience of physical activity — breathing changes, sweating, increased pulse — can mimic the signs and symptoms of anxiety or panic disorder. But in the case of physical activity, these symptoms occur without emotional distress. In that way, exercise can help disconnect the pairing of physical symptoms with distress, Dr. Vickers-Douglas says. For people with panic disorder, it's the symptoms themselves that come to be feared. Associating something positive with those symptoms, instead of a panic attack, for instance, can help you learn how to manage the symptoms and not live in fear of them, she says.

• Environmental reinforcement. Exercise also gives you an opportunity to experience positive social or environmental reinforcement. "Depression often makes people want to isolate themselves," Dr. Vickers-Douglas explains. "But by doing so, they miss out on experiencing positive interactions with others or their environment, such as a smile or kind word from a passerby, or the sights and sounds of nature."

• Positive coping skills. Doing something beneficial to manage your depression or anxiety is a positive and active coping strategy. Trying to manage your moods through excessive alcohol consumption or dwelling on the consequences of your negative mood are unhelpful coping strategies. Rather than waiting passively for depression or anxiety to change, taking active steps, such as increasing physical activity, can help you gain confidence in your ability to manage your symptoms, Dr. Vickers-Douglas says.

It's likely that no one single biological or psychological factor associated with physical activity is responsible for improving depression and anxiety. Just as mental disorders often have many different causes, exercise acts in many different ways.

"There's plenty of evidence to suggest that exercise is important for emotional well-being and is helpful in reducing symptoms of depression," Dr. Vickers-Douglas says. "It's true that less is known about how exercise affects mood. But there's no reason to wait until the direct, indirect and interactive influences of physical activity on mental health are fully understood. You can start taking advantage of the benefits of physical activity now."

Of course, knowing that something's good for you doesn't make it any easier to actually do it. Most people in the general population don't engage in any regular physical activity or quit shortly after starting an exercise program. Depression and anxiety can make it even more difficult to get active. By its nature, depression means that you don't enjoy activities, that you're often fatigued or sedentary, that you just don't feel like it, that you lack motivation, or that you don't stick to treatment regimens very well.

You may have a hard enough time doing the dishes, showering or going to work. How can you possibly consider adding exercise to the mix?

Overcoming that inertia can be daunting. Another challenge is maintaining, or adhering to, an activity program. Setting realistic goals, doing some problem solving, and recognizing that exercise won't always be fun or easy can help.

• Talk to your doctor. Although not all mental health professionals have adopted exercise as a part of their treatment regimen, talk to your doctor or therapist for guidance and support. Jointly assess your issues and concerns about an exercise program and how it fits into your overall treatment strategy.

• Identify what you enjoy. Figure out what type of exercise or activities you're more likely and less likely to do, as well as where, when and how often. For instance, would you rather garden in the evenings, jog in the pre-dawn hours, go for a brief walk in the woods or play basketball with your children after school?

• Set reasonable goals. Your mission doesn't have to be to walk for an hour five days a week. Even a 10-minute walk can help lift your mood, get you into a more positive environment and refocus your thoughts, even temporarily, away from negative or self-critical thinking patterns. Custom-tailor your plan to your own needs and abilities.

• Break it down. It might be good to have an overall exercise strategy. But focusing on the perfect plan or an ideal rather than what's realistic for you can sabotage your efforts. Don't start with the ideal and work backward. Start with the realistic and work forward. Break your program down into smaller parts. If you can't fathom walking for 45 minutes, what is possible? Fifteen minutes? Five minutes? Start there, and build on that foundation.

  "For many of us, just getting our shoes on and getting out the door is the majority of our effort. That's the hardest part," Dr. Vickers-Douglas notes. "Once we're moving, though, it's often easier to keep moving. So put your energy into the front end — into just getting started."

• Have short-term coping strategies. You may have a structured exercise program that calls for activity several times a week at the local gym. But plan for active ways to cope immediately and quickly with unexpected negative moods, depression, anxiety or other issues. For instance, even if it's your day off from exercise, taking a 10-minute walk may quickly help lift your mood if you're sad or anxious or find yourself focusing on negative thoughts. "Try to respond to a negative mood with physical activity," Dr. Vickers-Douglas says.

• Don't think of exercise as a burden. If exercise is just another "should" in your life that you don't think you're living up to, you'll associate it with failure. Rather, look at your exercise schedule the same way you look at your therapy sessions or antidepressant medication — as one of the tools to help your treatment. "Reframe the way you think about physical activity," Dr. Vickers-Douglas says. "Don't think of it as just another thing that you should be doing, but can't because of all of the demands in your life. Instead, think of it as something positive that you can do now to help you meet your goals, including feeling better physically and emotionally."

• Address your barriers. Identify your individual barriers to launching a program. If you're self-conscious, for instance, you might not want to exercise in public.

  If depression makes you feel like you're carrying a heavy weight around, the idea of moving on purpose, doing something active, can seem absurd. The barriers may feel overwhelming. But when you have depression, it's easy to overestimate difficulty. Instead, develop a strategy to overcome or get around those barriers. If you don't want to go to a crowded gym, perhaps you can go to a quiet park or use a home treadmill or bike. If you're put off by the thought of spending 30 minutes jogging, aim for five minutes of walking instead of just doing nothing. If five minutes seems daunting, try two minutes.

• Prepare for setbacks and obstacles. Exercise isn't always easy or fun. And it's tempting to blame yourself for that. People with depression are especially likely to feel shame over perceived failures. Don't fall into that trap. Give yourself credit for every step in the right direction, no matter how small, Dr. Vickers-Douglas says.

  "Chances are, you're going to come to a time when it gets really hard," she says. "If you say that you're a failure, that you blew it, that you have to start all over, you're more likely to quit altogether. Recognize that change is hard and setbacks are part of the change process. By learning how to cope with setbacks, you'll learn skills that will help you stay active over the long term."

Launching an exercise program is hard. Maintaining it can be even harder. "In the general population, most people who start an exercise program quit after a few months," Dr. Vickers-Douglas says. "For people with depression, making change and sticking to it can be even more difficult."

A key to exercise maintenance is problem solving. "What would happen if you went out to your car and it wouldn't start?" Dr. Vickers-Douglas asks. "You'd probably be able to very quickly list several strategies for dealing with that barrier, such as calling an auto service, taking the bus, or calling your spouse or friend for help. You instantly start problem solving."

But most people don't approach exercise that way. What happens if you want to go for a walk but it's raining? Most people decide against the walk and don't even try to explore alternatives. "With exercise, we often hit a barrier and say, ‘That's it. I can't do it, forget it,’ " Dr. Vickers-Douglas says.

Instead, problem-solve your way through the exercise barrier, just as you would other obstacles in your life. Figure out your options — walking in the rain, going to a gym, exercising indoors, for instance.

"Some people have the idea that being physically active is supposed to be easy and natural," Dr. Vickers-Douglas says. "Some think of it as just having enough willpower. But that really oversimplifies it and can make us feel like failures. You can't just rely on willpower. Identify your strengths and skills and apply those to exercise. Change isn't simple, but taking a series of simple steps in the right direction can be very effective. Just figure out what is the very first step for you."

In the end, the psychological payoffs can make that effort worthwhile.

"I really believe in empowering people to take an active role in their treatment," Dr. Vickers-Douglas says. "And physical activity can be an important part of that."