Your body can adapt to stressful stimulus. For example, resistance exercise triggers increases in muscle mass.
But if you stop the training stimulus, you slowly lose these adaptations.
However, some adaptations may be permanent, according to researchers from the University of Oslo.
Have you ever had a long layoff from resistance exercise? How did your body respond once you started training again?
It is much easier to regain your old fitness level, than it was to reach that level in the first place. This phenomenon is called muscle memory.
What is the mechanism behind muscle memory? Is it simply that people learned what kind of training is effective for them?
Another possibility is the central nervous system.
The central nervous system controls your muscles and training learns it to be more efficient at this. Thus, “muscle memory” might actually occur in the CNS.
The researchers had another idea. They speculated that myonuclei (nucleus in the muscle fibers) might be involved. The nucleus is the control center of a cell. As muscle fibers grow, they need more nuclei to keep up with the increase in muscle volume.
The researchers wanted to find out how myonuclei react to training and detraining.
They damaged one of the leg muscles of mice. Therefore, the other leg muscles had to work harder to compensate. After 21 days, this overload resulted in muscle growth.
In addition, the number of myonuclei increased. This happened before the increase in muscle mass as can be seen in the figure below.
This supports the notion that the number of myonuclei needs to increase to support an increase in muscle mass.
In a second experiment, leg muscles were overloaded in similar fashion for 14 days. Next, the researchers cut the nerves to the muscle to prevent muscular activity. As these muscles can’t be used anymore, this results in a detraining effect.
As expected, this decreased muscle size after 14 days.
However, the amount of myonuclei did not decrease as can be seen below. In a third experiment, they found that the amount of myonuclei did not decrease after 3 months either.
The researchers speculate that myonuclei are retained even after prolonged detraining. More myonuclei means faster and more capacity to adapt to training.
The researchers suggest that it might be wise to fill up muscle fibers with myonuclei when you are young. This might help prevent muscle weakness as you get older.
Anabolic steroids have been shown to increase the number of myonuclei.
Thus, the benefits of steroids might be permanent. The researchers conclude this should be taking into account when athletes are caught using steroids.