They lack six-pack abs. They could lose a few. Yet they're happy, body and soul. How are such people possible in body-centric America?

They exercise. They work out. It's part of their routine. Maybe not as often as they would like or think they should, but they do something.

Sure there are the long-term benefits like lowering your blood pressure, improved strength and endurance, a trimmer physique and the confidence that follows, increasing mental alertness, and reducing your odds of cancer, diabetes and heart disease . But exercise simply makes you feel good.

It is no sure-fire happy pill, and some say it has to be intense, or anaerobic (involving short energy bursts that cause the body to run out temporarily of oxygen), to bring on the psychological boost, but it is a part of the feel-good equation, experts say.

The problem with the perfect workout

Many Americans forget or ignore both the short- and long-term benefits and avoid exercise due to a sedentary lifestyle, allowing a "perfect" workout to be the enemy of one that is "good enough," and boredom due to repeating the same exercise routine over and over, says Debbie Mandel, author of "Turn On Your Inner Light: Fitness for Body, Mind and Soul" (Busy Bee Group, 2003).

Two primary chemicals involved in making exercise feel good are cortisol and endorphins.

Cortisol is a hormone produced by the body under stress, such as anger, anxiety or fear, and it ultimately inflames and damages our organs. Exercise burns cortisol, and thereby makes us healthier and happier, Mandel says.

Endorphins are morphine-like hormone molecules that enter the brain's neurons and park on receptors that normally send pain-signaling molecules back to other parts of the brain. Some say endorphins are even more powerful and yield a more euphoric feeling than opiate drugs such as morphine and opium, which park on the same receptors when introduced to the body.

Exercise stimulates the brain's pituitary gland to release endorphins, an abbreviation for endogenous (meaning "produced within") morphine, in the bloodstream.

Get started

Even with a stagnant gym membership or so-so discipline, individual episodes of intense exercise provides psychological boosts aside from the harder-to-see, harder-to-acquire physical and disease-fighting benefits of exercise.

A single exercise session lasting 20 or 30 minutes at 80 percent of your capacity brings on pain-relieving endorphins, according to work by Robert G. McMurray of the University of Carolina at Chapel Hill.

Mandel agrees that even one session makes you feel better and clears your head. "Once you make a commitment to exercise then you are motivated to keep feeling good every day. After about two weeks of exercise you stay on course," she said in a recent email interview.

Mandel says you can ensure a psychological reward if you tailor your workout level to your stress level. "If you are highly stressed, you need to do a more intense workout which means longer than 30 minutes; if you are less stressed, then 30 minutes should suffice," she says.

Heavy lifting

Some scientists say the feel-good benefits vary with the type of exercise. Research by Ed Pierce, now at Bridgewater College, and his colleagues shows that moderate exercise and light weightlifting or other resistance training, while critical for overall health, fail to bring on endorphins.

Alan Goldfarb of the University of North Carolina-Greensboro also says endorphins are only associated with heavy weightlifting or any kind of exercise during which you sprint (such as during running, biking, swimming).

Some experts say that tolerance to endorphins increases over time, but Mandel also says this varies with the person.

"Mostly, you get a consistent high from a workout to music and a workout that you enjoy," she says. "It is important to realize that routine deadens the heart, and you have to change up your exercise regimen. The body always adapts and you need to challenge it. So, vary the intensity, cross train, take dance classes, try a new sport, use a personal trainer for a few sessions, etc. Keep it fresh, and you will get that high!"