Progressive overload means gradually increasing the demand you place on a
muscle, so it has a reason to adapt. In practice that is usually a little more
weight, one more repetition, or one more set than you managed last time on the same
exercise.
It is the principle underneath almost every strength programme ever written. The catch
is that it only works if you know what you did last time. Beat a number you cannot
remember and you are not overloading, you are guessing. That is the plateau most people
hit, and it is a bookkeeping problem rather than a training one.
Progressive Overload is a free gym workout tracker for Android, made by
an independent developer. It does that bookkeeping, and
answers the question beginners actually have: what am I supposed to do, and how do I do
it? New to all of this? Start with
progressive overload for beginners.