Author: Troy Theodosiou
Most studies show that muscle loss doesn’t begin until after two or three weeks of complete detraining. That means no weightlifting or formal exercise of any kind.
It is important to note that these studies may have overestimated muscle loss because of the tools they used to measure body composition.
More often than not, scientists only measure total lean body mass (LBM), that is, everything in your body that isn’t fat. If your LBM goes down, then it’s generally assumed that you’ve lost muscle.
Muscle isn’t the only thing that contributes to your lean body mass, though.
Glycogen is a substance that is deposited in bodily tissues as a store of carbohydrates. For every gram of glycogen that is stored, an additional three to four grams of water is stored together, the added glycogen and water can increase muscle volume by about 16%.
When you stop training, one of the first things that happens is that there is a drop in muscle glycogen levels.
After one week of detraining, your muscle glycogen levels can drop by 20%, and after four weeks your glycogen levels are close to half of what they normally are.
The drop in water and glycogen can cause muscle volume to shrink about 10 percent over the course of a month. This loss of lean mass returns quickly when people start lifting weights and eating more carbs.
Despite the fact that studies have shown lean mass starts to disappear after about two or three weeks, it may take slightly longer for you to lose actual muscle.
The good news is that when you start lifting weights again, you can expect to gain size and strength faster than you did the first time around!
This scientifically verified phenomenon is known as “muscle memory.”
The answer to this enigma begins with an interesting fact about muscle cells themselves: they’re much larger than most other cells and are one of the few multinuclear cells in the body. This means that they don’t contain just one nucleus but many.
As you overload your muscles with resistance training, new nuclei are added to the muscle cells, which then allows them to grow larger. In fact, the number of nuclei within the muscle fibers is one of the most important factors that regulates muscle size.
It turns out that while an extended break from the gym clearly results in smaller, weaker muscles, the new nuclei added during the training period are retained for at least 3 months of inactivity. Some evidence shows that these new nuclei are never lost, meaning that strength training permanently alters the physiology of muscle fibers.