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(The Conversation) – Getting in shape is not easy. But after all that hard work, how long do we really keep it? It turns out that, even with the great effort we put into training, taking time off can mean losing shape much faster than it takes us to get fit. To understand how the body loses shape, we first have to understand how we get into shape. shape. The key to getting in shape, whether it’s improving cardiovascular fitness or muscle strength, is to overcome your “usual load.” This means doing more than what our body is used to. The stress this places on our body makes us adapt and be more tolerant, leading to a higher level of fitness.
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The time it takes to get in shape depends on several factors, such as physical level, age, intensity of exercise, and even environment. But some studies indicate that even six interval training sessions can increase maximum oxygen consumption (V02 max), a measure of general fitness, and improve our bodies’ effectiveness in fueling itself by using the sugar stored in our muscles. cells during exercise.
In the case of strength training, an increase in muscle strength can be seen in as little as two weeks, but changes in muscle size will not be seen until 8-12 weeks.
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When we stop training, how quickly we lose fitness also depends on many factors, including the type of fitness we are talking about (such as strength or cardiovascular condition).
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As an example, consider a marathon runner, who is in top athletic shape and can run a marathon in two hours and 30 minutes. This person spends five to six days a week training, running a total of 90 kilometers. He has also spent the last 15 years developing this level of fitness.
Now let’s say you stopped training completely. As the body no longer has the training stresses that force it to stay in shape, the runner will begin to lose his physical form in a few weeks.
Cardiorespiratory fitness, indicated by 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 stops training. This rate of decline continues, but at a slower rate for longer periods.
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Interestingly, although highly trained athletes, such as our marathon runner, record a sharp decline in V02 max in the first four weeks, this decline eventually stabilizes and, in fact, maintain a higher V02 than the average person.
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But for the average person, V02 max drops sharply, returning to pre-workout levels, in less than eight weeks.
The reason why the V02 max. This decrease is due to the reduction in blood and plasma volumes, which decrease by up to 12% in the first four weeks after a person stops training. The plasma and blood volume decreases due to the lack of tension that is exerted on our heart and our muscles.
Plasma volume can even decrease by around 5% in the first 48 hours after stopping training. The effect of decreased blood and plasma volume causes less blood to be pumped through the body with each heartbeat. But these levels only go down to the starting point, which means that we do not get worse.
Of course, most of us are not marathon runners, and 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.
In terms of strength, tests show that, in the average person, 12 weeks without training causes a significant decrease in the amount of weight we can lift. Fortunately, research shows that some of the strength you gained before you stopped training is maintained. What is intriguing is that, despite the significant decrease in strength, there is a minimal decrease in the size of the muscle fibers.
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The reason we lose muscle strength largely has to do with the fact that we are no longer stressing our muscles. Therefore, when we are no longer working our muscles hard, they become “lazy”, which causes the number of our muscle fibers to decrease, and less muscles are used during an activity. This ultimately makes us less able to lift the heavy loads that we used to lift.
The number of muscle fibers used during exercise decreases by around 13% after two weeks without training, although this does not appear to be accompanied by a decrease in muscle strength. This implies that the losses observed in the longer periods of “detraining” are a combination of both this initial decrease in the number of muscle fibers we use and the slower decrease in muscle mass.
In the case of a person who goes to the gym and lifts weights, they will experience a decrease in the size of their muscles and, over time, it will be more difficult to lift heavy loads with fewer muscle fibers working.
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So even after all that effort to get fit, we start to lose cardiovascular capacity and strength within 48 hours of quitting. But we didn’t start to notice these effects for two to three weeks for cardiovascular fitness and 6-10 weeks for strength. The “detraining” rates are similar for men and women, and even for older athletes. But the more fit you are, the more slowly you will lose what you have gained.
– Dan Gordon is Associate Professor of Cardiorespiratory Exercise Physiology at Anglia Ruskin University. Justin Roberts is associate professor of health and exercise nutrition at Anglia Ruskin University.
Published under a Creative Commons license by The Conversation.
Editor’s note: This note was initially published in May and was updated in July 2021.