Even when you sit perfectly still, there are muscles throughout your body that are constantly moving. Muscles enable your heart to beat, your chest to rise and fall as you breathe, and your blood vessels to help regulate the pressure and flow of blood through your body. When we smile and talk, muscles are helping us communicate, and when we exercise, they help us stay physically fit and healthy.

Usually, when you exercise other parts of your body, your heart redirects blood from your hands to exercising muscles. This cools the skin and local tissues of the hand. The blood vessels in your hand try to maintain circulation but may overreact, leading to a local increase in blood and possibly swelling.

Since there are many possible specific reasons why exercise could be inhibited, this is a rather slippery term. For instance, the patient may experience unusual breathlessness (dyspnea), muscle pain (myalgia), or increasing muscle weakness while exercising, or may, after exercise, experience severe headache, nausea, or extreme fatigue. In most cases the specific reason that exercise is not tolerated is of considerable significance when trying to isolate the cause down to a specific disease.

Many diseases have exercise intolerance as one of the only symptoms, as in the case of some of the less severe metabolic myopathies. Nonspecific fatigue or pain syndromes such as chronic fatigue syndrome, fibromyalgia and Overtraining Syndrome are all collections of symptoms, one of which is likely to be exercise intolerance.

Caffeine is a central nervous system (CNS) stimulant, having the effect of temporarily warding off drowsiness and restoring alertness. Beverages containing caffeine, such as coffee, tea, soft drinks and energy drinks enjoy great popularity.That morning cup of coffee may be an antidote to post-exercise muscle soreness, if preliminary research is correct.

Muscle cramps are involuntary and often painful contractions of the muscles which produce a hard, bulging muscle.

In a small study of female college students, researchers found that a caffeine supplement seemed to lessen the familiar muscle pain that crops up the day after a particularly challenging workout.

Known as delayed-onset muscle soreness, or DOMS, the pain is common in the day or two after a workout that was more intense than normal. Exercise that involves eccentric contraction of the muscles is particularly likely to cause delayed muscle pain.

In eccentric contraction, the muscle produces a force while it's being lengthened. This happens when a person runs downhill, for example, or lowers a weight during a bicep curl.

Exercisers and researchers alike have tried many ways to prevent DOMS -- including over-the-counter painkillers, stretching and massage -- but studies have found no cure-all for the problem.

In the current study, published in the Journal of Pain, researchers at the University of Georgia in Athens looked at the effects of a caffeine supplement on delayed muscle pain in nine young women.

First, in a simulated workout, the researchers used electrical stimulation to produce eccentric contractions in the women's thigh muscles -- enough to cause moderate day-after soreness.

Next, they repeated the procedure over the next two days, but on each day, the women took either a caffeine pill or placebo pill one hour before the muscle workout. Neither the women nor the researchers knew which pill was given on which day.

Overall, the women reported significantly less muscle soreness during the workout when they took caffeine instead of the placebo. The supplement had about the amount of caffeine found in two cups of coffee.

The theory is that caffeine eases delayed muscle pain by blocking the activity of a chemical called adenosine, which is released as part of the inflammatory response to injury. Adenosine can activate pain receptors in body cells, explained Victor Maridakis, the study's lead author.

In this study, he told Reuters Health, the pain relief with caffeine was stronger than that from painkillers like acetaminophen (Tylenol) and naproxen (Aleve).

Maridakis noted that research into another popular pain reliever, ibuprofen, has shown inconsistent results, and it's unclear whether the drug -- sold under brand names like Advil and Motrin -- aids delayed muscle soreness.

Before downing a couple cups of joe before your workout, however, Maridakis recommends careful consideration of the possible side effects of caffeine. A few studies indicate that large amounts of caffeine — the equivalent of six cups of coffee a day — may slightly enhance weight loss in people who exercise and maintain a low-fat diet. But no studies indicate that weight loss from large amounts of caffeine is significant or permanent. There's also no evidence that increasing caffeine intake alone has any effect on weight loss.

"The negative side effects of caffeine are increased feelings of anxiety, heart palpitations, increased blood pressure, upset stomach, increased urination and disrupted sleep," he explained. "Caution should be used when consuming caffeine so not to exacerbate these side effects."

Though most people are "normal responders" to caffeine, Maridakis noted, some are hypersensitive to it and are at higher risk of side effects.

On the other end of the spectrum are the caffeine-resistant types. People who drink a couple cups of coffee a day tend to become desensitized to caffeine, the study authors point out, and it's unclear whether a dose of caffeine would aid their post-workout muscle pain.

Exercise is key for both heart and back patients, and a variety of specific exercise techniques are available for both groups. Some exercise specialists (e.g., physical therapists, trainers) are trained in modifications specific to these patients.Tips may help some people to prevent exercise induced muscle pain:

• Before you exercise, remove your rings and loosen your watchband.
• During exercise, do occasional forward and backward arm circles.
• Occasionally stretch your fingers out and then make a fist. Repeat this several times during exercise.