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Falling out of shape may take a few weeks, researchers say

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There are many factors that determine how quickly we lose shape after we stop exercising.

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Getting in shape is not easy. But after all of this hard work, how long do we actually keep it up? It turns out that even the great effort we put in training, taking some free time can mean that we become “unfit” much faster than it took us to get in shape.

To understand how the body becomes “unfit” we must first understand how we become fit. The key to getting fitter, whether it’s improving cardiovascular fitness or muscle strength, is to go over the “usual load”. It means doing more than what our body is used to. The stress this has on our bodies causes us to adapt and become more tolerant, which leads to higher levels of fitness.

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The time it takes to get in shape depends on a number of factors, including level of fitness, age, intensity of your workout, and even the environment. But some studies indicate that even just six interval training sessions can lead to an increase in peak oxygen uptake (V02 max) – a measure of overall fitness – and improve the efficiency with which our bodies are able to. to eat using the sugar stored in our cells. during exercise.

For strength training, some muscle strength gains can be seen in as little as two weeks, but changes in muscle size will only be seen around 8 to 12 weeks.

When we stop exercising, how quickly we lose fitness also depends on many factors, including what type of fitness we are talking about (like strength or cardiovascular fitness).

Take the example of a marathon runner, who is in great sporting shape and can run a marathon in two hours and 30 minutes. This person trains five to six days a week and runs a total of 90 kilometers. They have also spent the last 15 years developing this level of fitness.

Now let’s say that they have completely stopped training. Because the body no longer has the stress of training forcing it to stay in shape, the runner will start to lose shape within a few weeks.

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Cardiopulmonary form – indicated by a person’s V02 max (the amount of oxygen a person can use during exercise) – will decrease by about 10% in the first four weeks after a person stopped training. This rate of decline continues, but at a slower rate over longer periods of time.

Oddly, although highly trained athletes – like our marathon runner – see a sharp drop in V02 max in the first four weeks, that drop eventually balances out, and they actually maintain a higher V02 than the person’s. average. But for the average person, V02 max drops sharply, returning to pre-workout levels, in less than eight weeks.

The reason V02 max decreases is due to reductions in blood and plasma volumes – which decrease by up to 12% in the first four weeks after a person has stopped training. Plasma and blood volume decrease due to the lack of stress on our heart and muscles.

Plasma volume may even decrease by about 5% within 48 hours of stopping training. The effect of decreasing blood and plasma volume leads to a decrease in the blood pumped through the body with each heartbeat. But these levels only go down where we started, which means we’re not going to get any worse.

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Of course, most of us are not marathon runners, but we are not immune to these effects either. As soon as we stop exercising, the body will begin to lose these key cardiovascular adaptations at a rate very similar to that of highly trained athletes.

When it comes to strength, evidence shows that in the average person, 12 weeks without training results in a significant decrease in the amount of weight we can lift. Fortunately, research shows that you retain some of the strength you gained before you quit exercising. What’s intriguing is that despite the significant decrease in strength, there is only a minimal decrease in muscle fiber size.

Much of the reason we lose muscle strength is that we no longer put stress on our muscles. So when we stop working our muscles hard, the muscles become ‘lazy’, resulting in a decrease in the number of our muscle fibers and fewer muscles recruited during an activity – making us less able to lift the heavy weights than we do. used to do. .

The number of muscle fibers used during exercise drops by around 13% after just two weeks without training, although this does not appear to be accompanied by a decrease in muscle strength. This implies that the losses observed during the longer periods of “de-training” are a combination of both this initial drop in the number of muscle fibers we use, but also the slower decline in muscle mass.

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For the average athlete who lifts weights, they would experience a decrease in the size of their muscles – over time it would be more difficult for them to lift heavy loads because they recruited fewer muscle fibers.

So even after all these efforts to get in shape, we start to lose cardiovascular fitness and strength within 48 hours of quitting. But we don’t start to feel these effects for at least two to three weeks for cardiovascular fitness and around 6 to 10 weeks for strength. The rates of “de-training” are similar for men and women, and even for older athletes. But the fitter you are, the slower you will lose your gains.

Falling out of shape may take a few weeks, researchers say

Dan Gordon is Associate Professor of Cardiorespiratory Exercise Physiology at Anglia Ruskin University. Justin Roberts is Associate Professor of Health Nutrition and Exercise at Anglia Ruskin University.

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