This question has been around as long as man has lifted weights.
Delayed onset muscle soreness (DOMS) is really a misnomer.
I don’t believe human muscle has the nerves necessary to register
pain. (Think intramuscular injections for instance.) But clearly some-
thing is getting sore, but I have no clue what and neither does
anybody else.
DOMS is primarily caused by eccentric “exercise”, although I have
have experienced incredible soreness as a result of static contraction
(think forearms in rock climbing for instance) and never from just
concentric exercise. Interesting.
In exercise, it is not necessary nor desirable to induce DOMS and
is for the most part avoidable if one takes the proper precautions.
Now . . . and in an attempt to answer your original question “Are
DOMS an Indicator of Growth?” I would say no from my personal
experience although I do know, when I was growing, and growing
fast, I was not sore (but could make myself sore if I wanted to) but
my muscle did “feel” different, not sore, but always tight and full
during these growth spurts.
And lactic acid absolutely nothing to do with it. That is just so far
out in left field I don’t have neither the time nor the inclination, will
not even attempt to answer the whys and wherefores . . .