Below you will see extracts from the journal paper and quotes from the senior author. 

Key points from the paper

Training studio folklore suggests that previous strength training, with or without the use of anabolic steroids facilitates re-acquisition of muscle mass even after long intervening periods of inactivity. This “muscle memory” has previously been attributed to motor learning, but our data suggest the existence of a cellular memory residing in the muscle fibres themselves.

Muscle fibres have multiple nuclei, and the number of nuclei increases when muscle mass increases.

When mice were briefly treated with steroids the muscle mass and number of nuclei increased. The drug was subsequently withdrawn for 3 months and the muscle mass returned to normal, but the excess cell nuclei persisted. When such muscles were subjected to overload they grew by 30% over 6 days while controls grew insignificantly.

Our data suggest that previous strength training might be beneficial later in life, and that a brief exposure to anabolic steroids might have long lasting performance-enhancing effects.

Quotes from Gundersen

Mice were briefly exposed to steroids which resulted in increased muscle mass and number of cell nuclei in the muscle fibres. Three months after withdrawal of the drug (approximately 15% of a mouse's life span) their muscles grew by 30% over six days following load exercise. The untreated mice grew insignificantly. 

The results in our mice may correspond to the effects of steroids lasting for decades in humans given the same cellular ‘muscle memory’ mechanism. The new results might spur a debate on the current World Anti- Doping Agency (WADA) code in which the maximum exclusion time is currently two years.