The short answer is…it depends on your original level of fitness.
So how fast do you lose your fitness once you stop? If your a recreational exerciser…someone who works out 2 to 3 times a week, it takes 2 to 4 weeks of inactivity for any notable change in your conditioning. For an athlete or someone who has trained for 12 months or more, the declines are more gradual. For instance, studies have found that well trained athletes that have stopped all exercise, lose on average a little more than half their gains in aerobic conditioning in a 3 month lay off. Where as, a recreational person undertaking a 2 month exercise regimen, will lose all their aerobic gains if they stopped exercising for 2 months after the regimen.
Regardless of your fitness level, detraining affects different parts of your body…your cardiovascular system, your muscles and your waistline in different ways. The first thing to slide is your aerobic fitness…for the recreational exerciser this occurs after 10 to 14 days of little or no physical activity, the body’s ability to effectively consume and use oxygen begins to decline. The heart also gradually loses its ability to handle extra blood flow and those new capillaries begin to wither…however this can be reversed once you start exercising regularly again. Taking time out is a good idea, even elite athletes do this but instead of stopping completely try some active recovery. Do something different like mountain biking, swimming, hiking…even if its only once or twice a week.
The detraining effect seems to be less for muscular strength and endurance during the first few weeks of inactivity. But after 4 weeks muscle fibres begin to shrink and sometime between then and eight weeks that decline becomes more measurable. Muscles will feel less firm and those 6 pack abs may start to sag.
If using exercise to keep the weight off, this period of inactivity will have an impact on your weight. If your daily workout was burning 300 to 400 calories and you want to maintain your weight, you need to reduce your intake by 300 to 400 to match. Whats less simple is how those extra calories might look on your body. Fat and muscle are two different types of tissue. If you stop working out, your muscles will eventually shrink back to where they started. If you eat more calories than you burn, the extra calories will be stored as fat.
So how to stop the slide? As mentioned above, don’t stop completely…keep active, do something different. As they say a change is as good as a rest. If injured there will be some other exercise you can do, whether thats rehab or cycling instead of running which will help maintain some of your conditioning. As an athlete I always took 4 weeks off a year but I didn’t stop completely…this was my off season and it gave me valuable time to freshen up and recharge the batteries. Exercise during this time was recreational, no structured program…when I wanted, which was about 3 times a week and the intensity and mileage was low.
If your considering stopping exercise completely for several months, bear in mine, its difficult to predict exactly how long it will take to return to your former fitness level. After a break of 3 months its unlikely you will return to peak condition in a week. It may take as long as 3 months to regain all your conditioning. The actual time it takes to regain your fitness depends on your original level of fitness and how long you’ve stopped for.