Most body composition researchers and experts agree on the following:

  1. Most guys can gain 15-to-25 pounds of muscle in their first year of proper strength training (and women should cut those numbers in half).
  2. Most people can gain about half as much muscle in year two than in year one.
  3. Most people can gain about half as much muscle in year three than in year two.

Opinions diverge on what happens next, though. 

Some authorities claim that muscle growth becomes vanishingly small after four-to-five years of proper strength training and eventually comes to a standstill. Others disagree and say that although muscle growth slows down considerably with each successive year of training, it never stalls altogether (“there’s always another pound to be gained”).

The truth is somewhere in the middle. 

It’s beyond dispute that the rate of muscle gain decreases as training experience increases until it’s a fraction of what it was in year one, but there’s no scientific evidence that the nadir is always zero pounds per year. 

That said, we do know that most natural bodybuilders and athletes reach a point where progress is so slow it’s almost impossible to see or measure and thus might as well be zero.

This phenomenon could be caused by a genetic or physiological ceiling on muscle growth, but it could also be mostly a function of the practical limits of training volume and intensity. That is, while a highly trained guy or gal might technically be able to gain more muscle or strength, the training rigors required to achieve it might be too much for their body to handle. Especially as they get older.

So, I like to think of our absolute potential for muscle gain as an asymptote—a point we’re continually moving toward but never quite reach, like flawless verbal fluency or a perfect golf swing. 

And that means that while most of us can’t gain a considerable amount of muscle after our first few years of proper strength training, we can still continue to make some progress for the coming years and possibly even decades.