One of the realities of getting fit is if you stop training you will slowly lose the gains you worked so hard to achieve. Conventional wisdom says this is true of strength training and aerobic conditioning. This phenomenon is known as the principle of reversibility and is sometimes called detraining. If you don’t continue to train, you lose the fitness gains you incurred. Makes sense, doesn’t it? You don’t need extra muscle or superior cardiovascular fitness if you aren’t moving as much.
But, wouldn’t it be nice if the strength gains you make were permanent? Surprisingly, there is preliminary evidence that once you’ve strength trained for a while and your muscles adapt to that training, some of those adaptations may be permanent. Keep in mind, though, the evidence comes from animal research.
Can Muscles Be Permanently Changed by Strength Training?
In one study published in the Proceedings of the National Academy of Science, researchers found preliminary evidence that some changes that happen to muscles in response to strength training are long-lasting. One way muscles adapt to strength training is to form more muscle myofibrils. These are the contractile elements of a muscle cell, the components that give a muscle the ability to contract with more force. They also lay down new nuclei within the existing muscle fibers and this happens even before the muscle changes in size. The nuclei within muscle cells are “command central” for a cell. The nucleus contains the muscle cell’s genetic information and is the site where replication of DNA takes place, the first step in the synthesis of new muscle proteins.
The researchers found when mice went through a training program, they laid down new muscle nuclei, but even when the mice stopped training, the nuclei remained. The mice gradually lost muscle mass when they stopped training, but the nuclei didn’t disappear. Having those extra nuclei inside muscle cells gives muscle cells a jumpstart for growth if training restarts. The DNA in the nuclei are primed to replicate DNA and restart the building of new muscle proteins. The nuclei that form during strength training may be long-lasting. Even after the researchers removed the nerve supply to the mice’s muscles for 3 months, the nuclei they had accumulated remained.
How do muscle cells get those extra nuclei? Satellite cells, located around the muscle fiber, donate nuclei to the muscle cells that need them to grow. Satellite cells are precursor cells that muscle cells can call upon when they need additional support, in this case, more nuclei for growth. The additional nuclei fire up muscle growth.
Muscle Memory: Yes, Muscles Remember!
You’re probably already familiar with the concept of muscle memory. If you hypertrophy and strengthen a muscle and then stop, you will gradually lose some of the strength and size it gained. Yet getting that muscle and strength back is faster the second time around. You may have spent 6 months to accumulate your strength. But if you take a long break and lose those gains, you might get them back twice as fast. What took you six months to build, you regain in three months. That makes taking time off a little less intimidating, right?
One of the reasons muscles can recoup their gains so quickly is because the extra muscle nuclei are already there and ready to go. There’s also a neural component to regaining strength. The brain keeps a record of the muscle recruitment patterns for specific exercises. Even if you take a long break, your brain still recognizes the movement patterns you previously learned to do a certain exercise. For example, you probably learned to ride a bike as a child, but even if you haven’t ridden in decades, you can jump back on and go for a spin.
When You Start Strength Training May Matter Too
According to the study in Proceeding of the National Academy of Science previously mentioned, the earlier you start strength training, the more likely you are to lay down muscle nuclei that last. It looks like the ability to add new muscle nuclei is reduced in older animals and, possibly, humans too. However, the ability to lay down new muscle nuclei doesn’t decline until the last third of life. Although older humans can build muscle size and strength, it may not be as easy for them to add and retain nuclei. This is a disadvantage if an older person stops training for a while. So, it’s best to begin strength training before late middle-age, although anyone, regardless of age, can benefit from training.
Another point to remember. The stronger you are when you take a long break, the faster and easier you’ll make a comeback. The results of these studies suggest that we should start training during early and middle adulthood and continue training throughout life. But, if you need to take a break, you have the framework set up to make gains faster after you make a comeback.
The Timetable of Detraining
How long does it take to lose strength and muscle size? We hold on to strength gains longer than we retain gains in aerobic capacity in response to cardiovascular training. You can take a two-week break from strength training and retain most of your strength. However, you may lose some muscle endurance. In one study, participants lost only 12% of their muscle strength after two weeks and 7% of their fast-twitch muscle fibers. Other studies show after two weeks the loss is even less.
But, the longer you don’t train, the greater the losses. For example, in one study, powerlifters lost 35% of their strength after seven months of not training. However, research suggests that doing some training, even as little as once per week, greatly reduces or even prevents the loss of muscle size and strength due to detraining. If you don’t train at all, you’ll start to see a gradual decline in strength and power after 3 weeks. However, the loss will be slower if you trained hard before taking the break.
The Bottom Line
Muscles really do have memory and even long-term memory. There’s even some evidence that strength training changes a muscle’s structure by adding more muscle nuclei. Thanks to the presence of more muscle nuclei and muscle memory, you recoup your strength faster.
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Sports Med. 2013 May;43(5):367-84. doi: 10.1007/s40279-013-0031-3.
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