You worked hard at achieving your level of fitness and your stamina. You really don’t want it to be gone.  But if you skip your workout for only two weeks, this is what might happen. At least to a certain extent.

While people who are in shape can generally regain their fit physique easier than those who are starting from scratch, it may sound somewhat surprising that your body can fall so quickly out of shape. The phrase "use it or lose it" definitely applies when it comes to your muscle strength, cardiovascular fitness, stamina and more.

On the up-side, positive changes happen fast when you exercise frequently. For example, after just a few strength-training sessions neuromuscular adaptations occur, which means your brain has an easier time communicating with your muscles so you can use them more efficiently.

After exercising for only over one week (assuming you've gotten your heart pumping), you'll enjoy increases to your plasma and blood volume and, as you carry on, to your muscle mass and strength.

These gains can be transitory, however, if you don't keep on working out, and once they've vanished you'll have to work hard to get back to where you left. As a rule of thumb, it takes about twice as long to get back into shape as the time you've spent being inactive.

Let me start by saying that our body needs recovery time when we exercise, especially if we exercise at high intensity. Having said that, however, missing workouts for a fortnight will propel your body quickly into the "out of shape" classification.

After about 10 days to two weeks, your VO2 max, a measure of cardiovascular endurance, will begin to slide and carry on doing so at a rate of ½ % per day.

Indeed, a study found that after just 12 days devoid of exercise, VO2 max dropped by 7% while blood enzymes associated with endurance performance dropped by half.

Similarly, four weeks of idleness among endurance cyclists resulted in a 20% drop in VO2 max., keep in mind this is among competent athletes — among those new to exercise, gains in VO2 max completely vanished after four weeks of inactivity.

By contrast, however, strength loss among newbies, with studies showing newly made gains in strength tend to hold on even after months of inactivity.

For instance, among previously untrained men who engaged in a 15-week strength-training program, taking a three-week pause in the middle had no impact on strength levels at the end of the study.

Note that after three to four weeks of inactivity, your muscles will start to atrophy and your body will start to return to using carbs, rather than fat, for energy, which kick-starts insulin resistance.

Usually, if you're quite fit your body will remain in a fitter state longer than someone who's not as fit, even if you stop working out. If you're an Olympic athlete, for example, taking two weeks off at the end of the season may be just what your body needs.

The older you get, however, the faster your muscles atrophy if you're not engaging in regular exercise. Even more so, it will take you longer to regain it. Compared with 20- to 30-year-olds, 65- to 75-year-olds lost strength nearly twice as fast during six months of inactivity.

If you need to reduce your training time, incorporating some form of high-intensity exercise on a weekly basis seems to improve your chances of maintaining your conditioning, even if you can't resume your full fitness routine for several months.

In order to achieve this, you need to exercise at about 70% of your VO2 max at least once a week.

Just meeting the minimum requirement of 30 minutes of moderate physical activity a day, five days a week, can reduce your risk of death from any cause by about 20%.  Those who are involved in moderate intensity activity — a full seven days a week — further reduced their risk of death, to nearly 25%.

A separate study also found that, compared to those who exercised daily and often vigorously, sedentary people had a six times higher risk of dying from heart disease over the period of 15 years.

The greatest gains are often seen among people who go from being sedentary to physically activity, although benefits also increase with exercise frequency and intensity (to a point, as overdoing it likely to backlash).

I always tell my clients that the added bonus is that exercise not only extends life but also adds quality of life to those additional years.

All of those movements that you might currently take for granted, such as, walking up and down stairs, lifting your child, climbing a ladder to change a light bulb — are likely to become more difficult by the time you're in your 70s.

This is when sarcopenia (age-related muscle loss) tends to fast-track. You might start to feel weaker and find you can't do certain physical things, that you were previously capable of doing. But exercise can change that by helping you maintain muscle mass and strength (and even increase your muscle volume).

Simultaneously, exercise reduces the risk of chronic diseases to the extent that researchers described it as "the best preventive drug" for many common conditions, from psychiatric disorders to heart disease, diabetes and cancer.

It's worth noting, that walking 7,000 to 10,000 steps a day (which is just about 6 to 9 kilometres) in addition to your exercise program is also important for keeping your body in good condition.

One of the benefits of being fit is being able to take time off from exercise and use the "reserves" that were built up during your “down-tome”. If done infrequently, skipping a workout is unlikely to have adverse effect on overall fitness level, and in the examples that follow it is probably more advantageous than not.

• You're ill below the neck (i.e., you have coughing or chest congestion, fatigue, muscles aches, vomiting or stomach cramps)

• You have a fever

• You're injured (there are some cases when light exercise can benefit an injury; seek the opinion of a physical therapist or personal trainer if you're unsure)

• You're exhausted or depleted

You should also avoid workouts at part of your recovery process, although on your "off" days you might still do gentle exercise, like stretching or yoga, and you can still do your daily 10,000 steps.

As your fitness increases, the intensity of your exercise should goes up, and the frequency that your body can tolerate is reduced. As a consequence, I recommend that you continuously customise your program to your current fitness level and other lifestyle considerations.