Muscle mass grew by 30 percent
A research team at Oslo University, headed by Professor Kristian Gundersen, exposed the mice to anabolic steroids for two weeks, which resulted in increased muscle mass and an increase in the number of nuclei in the muscle fibres.
The drug was then withdrawn for three months, a period which corresponds to around 15 percent of a mouse's lifespan. After the withdrawal, the mice’s muscle mass grew by 30 percent in six days following load exercise, while untreated mice showed insignificant muscle growth during the same period.
This suggests that the steroids still had a clear effect on the muscles in the first group even after a long period with no steroid use.
Muscle memory
The specific time aspect is of course challenging to extrapolate from mice with a lifespan of two years to humans, who live for 80 years. However, the cell nuclei in humans are known to be very stable. If the muscle memory mechanism in humans is similar to what we observe in mice we could be talking about
several decades of advantageous effects.
Kristian Gundersen
The mechanism behind this effect can be described as a form of ‘muscle memory’, where an increased number of nuclei in muscle cells is maintained after temporary use of performance enhancing drugs.
Each nucleus can produce proteins for a certain volume of the cell. Thus, each nucleus and the associated synthetic apparatus can be viewed as a small protein factory that builds muscles. In principle, the more nuclei, the bigger muscles you can obtain.
“There is an accumulation of nuclei when you build muscles, and these nuclei seem to promote the gain of muscle mass with future exercise,” Gundersen says in
an article on the Oslo University website.