If someone lifts weights or takes a long jog after not doing it for a while, they can experience delayed onset muscle soreness (DOMS).
However, when they return to the same exercise days afterwards, the chance of a new DOMS episode occurring diminishes.
I used to think that it was partly due to muscle getting larger. However, an individual who trains themselves to lift 100kg, stops for 2 months and still manages to lift the same 100kg can experience DOMS (assuming that little has changed in the muscle size and force it can exert).
This leads me to ask: are there other biological phenomena involved, rather than just muscle size?