Skipping exercise for a week or two may cramp your mood, says a study that turned regular exercisers into couch potatoes.

"We were able to measure negative results from withdrawal of exercise in just two weeks," says researcher Ali Berlin, MS, in a news release. Berlin works at the military's Uniformed Services University of the Health Sciences. She presented her findings in Nashville, Tenn., at the American College of Sports Medicine's annual meeting.

Click here to read Web MD's "Exercise for Depression Rivals Drugs, Therapy."

Stick to It

The take-home message: Once you start exercising, keep it up. That doesn't mean becoming a slave to the Stairmaster or a fanatic about any particular workout. Adjustments may be necessary from time to time.

For example, "if someone is a regular jogger or bicyclist and find they cannot do the activity for a short time, they need to do something else like walking until they can resume their preferred activity," says Berlin.

Click here to read Web MD's "Can You Really Get Fit in 6 Minutes a Week?

Forced to Take a Break

Berlin's study included 40 regular exercisers. "We were not looking at elite athletes; the study participants were people who are regularly active at a moderate level," says Berlin.

First, the participants took mood and fitness tests. Next, half were forbidden from exercising for two weeks. The others were told to follow their normal fitness routine.

The tests were repeated one and two weeks later. The results showed that the forced exercise "vacation" didn't recharge anyone's batteries. Instead, it left the former exercisers feeling worse than before.

It's one of those strange-but-true health facts: The more active you are, the more energy you have. That is, as long as you're not ill or engaging in ridiculous amounts of exercise that push the body too hard.

The CDC recommends that adults get at least 30 minutes of moderate-intensity physical activity five or more days per week.

Click here to read Web MD's "Training for the Big Run."

No Exercise, Crummy Mood

"After one week we began to see changes," says Berlin. After two weeks, those changes had deepened. Two weeks of slothfulness had pushed the former exercisers into a grim state.

By then, they were significantly more tense, tired, and less vigorous. The more out of shape they became, the more their mood and energy level worsened. "What this tells us is that any interruption in a regular fitness routine can have a negative [impact]," says Berlin.

So what's a person to do when the weather is miserable or time seems scarcer than usual? Get creative. Tweak your routine, choosing other activities to stay physically and mentally fit, Berlin suggests.

Health care workers may also want to keep an eye out for depression symptoms in exercisers who get sidelined by injury or illness, she says.

Click here to read Web MD's "Better Late Than Never for Exercise."

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: American College of Sports Medicine 52nd Annual Meeting, Nashville, Tenn., June 1-4, 2005. News release, American College of Sports Medicine. CDC: "Physical Activity for Everyone: Recommendations."