If you've been sidelined by an injury, or you're considering taking a break from exercise, you might wonder if you'll lose your hard-earned strength and endurance. Some loss of fitness is inevitable, but there are ways to help minimize it.

Here's what happens to your body when you take a break from exercise.

Matters of the heart

The degree to which cardiovascular fitness declines during a period of de-training depends upon what kind of shape you were in to begin with. Individuals who are extremely fit, such as highly trained athletes, experience a rapid drop in fitness during the first three weeks of detraining, which then tapers off.

A significant level of fitness - higher than that of an untrained person - is retained for about 12 weeks. Individuals with low-to-moderate fitness levels show little change in cardiovascular fitness within the first few weeks, but their ability rapidly declines in the weeks immediately following.

Performance jitters

The ability to perform a given sport or activity, whether it involves swinging a bat in softball or running 10Ks, invariably declines when the sport is abandoned for any length of time. One study found that marathoners experienced a 25-percent decrease in endurance time during a maximal aerobic treadmill test after just 15 days of inactivity.

Another showed that swimmer's arm strength declined by more than 13 percent within four weeks of abandoning their regular training regimen.

Numerous variables come into play when analyzing the ability to perform a particular sport-specific skill, making it difficult to analyze the effects of detraining. Some are like riding a bike - you never forget how - while others, such as the ability to deliver an accurate serve in tennis, for example, involve specific timing and well-trained muscles.

Speaking of muscles...

With the exception of a genetically blessed few, most of us have to work at it building strength through formal or informal strength-training workouts. Again, well-trained athletes have the edge, because the positive effects of training remain evident weeks, sometimes even months, after ending training.

Lesser-trained individuals can expect to see their muscle strength and conditioning decline at a slightly faster rate, though not at the levels seen in sedentary individuals.

Stem the de-training tide

Experts agree that the best way to avoid losing much of the health and fitness benefits you've worked so hard to achieve is to do something. If you can't find the motivation to run for a few weeks or longer, try walking instead. Cross training became popular because it is a viable means of maintaining, even increasing, one's fitness level.

Runners can give their knees a break by switching to cycling, swimmers can work their legs on a stair stepper, and aerobics enthusiasts can take their workout outdoors by hiking through a local park or reserve.

If an injury is keeping you from your favorite activities, take your worries to the pool. Of course, it's always advisable to check with your physician before resuming exercise after an injury. Regardless of which activity you choose, be sure to progress gradually.

If boredom is the problem, now's the time to try that sport you've been considering for so long. In-line skating, tai chi, boot-camp workouts - whatever strikes your fancy. The key is to keep your heart and muscles challenged in order to minimize the detraining effects that come when taking a break from your usual routine.