weak? did you physically damage it? make sure the lights are not too far away.. if your using cfl's make sure thier 1-3 inches away from the top of the plant...
Try to bury the damaged part of the stem in soil...and squeeze tite. it should be fine if its just minor.
hey read this link I know this is not your case but you might find this interesting it has to do with pinching your branches so if u stay on top of your plant it could come back strong good luck Jmac https://www.rollitup.org/view.php?pg=faq&cmd=article&id=383
yes hes right ,, pinching your stems does work well ,, it breaks the inner part of the stem , & when it heals it will be ALOT stronger ,, kindda like a knot in a tree ...