http://www.physoc.org/press-release/2013/steroids-muscle
They did a study on mouses, giving them steroids.
(Steroids and resistance training both increase the amount of nuclei, so view it as resistance training, as nuclei is what they attribute the results too).
They then waited 3 months, or 15% of their lifetime.
They then made these previously doped mice, and also a control group exercise.
The previously doped Mice muscles grew 30% after the exercise, while there was no obvious difference in the control group.
Think of training your muscles as increasing the amount of volume your muscle cells can support. When you lose muscle, the volume of your cells decrease, but the ability for your muscle cells to support that size is still there. This makes retraining like blowing up a balloon that has already been stretched out, way easier, and way faster.
This effect is because the more myo-nuclei allows a higher rate of protein synthesis. More muscles require more myo-nuclei, to prevent breakdown, so they need more to for the same size to be maintained.
Although a beginner may have much less nuclei than an advanced lifter, they also have less muscle to maintain, so they can build muscle much faster.
But an atrophied advanced lifter will be able to generate muscle extremely fast, since they can synthesize muscle very fast, but have very little "upkeep"
Here is an chart to hopefully clarify:
| Protein breakdown/Day | Protein Synthesis Ability/Day | Net Possible gain/Day | |
|---|---|---|---|
| Beginner | -25g | +50g | +25g |
| Advanced | -100g | + 105g | +5g |
| Antrophied Advanced | -25 | +105 | +75 |
(This is just for example to explain, not actual or realistic values)
Source that myo-nuclei are not lost after resistance training:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2930527/
There is another principal in muscle memory with strength. This is because when your nervous system learns to do something, it never really forgets. This is why if you learn to ride a bike, in 20 years, you make be shaky, but you will pick it up very fast. Same thing with strength. This will also enhance your ability to gain muscle compared to a new lifter, as you can put additional stress on it.
What can we learn from this? Pain is temporary, but gainz are forever.