It is very common to get soreness/pain/DOMS when you do something you haven't done in a while (like skiing or bench) - Even when working far from max.

Is this because something with the muscles, or is it more related to what we are doing?

Is the training less effective at this point or will you gain more compared to how hard you work (because untrained muscles are easier to train)?(In relation to max).

Does this "regularness" effect continue into regular training? (If we compare doing something regularly/often compared to less regularly/often)

If you for example compare a program with many sets (Starting Strength), to one with few sets (4 hour body)?

Does this irregulars effect have a name? Is there some methodology for how to minimize it?

Practically for things I do like weights, hikings, Pilates, Yoga with some strength I want to minimize this effect (Be beeing "just regular enough")