Actually, yoga is rather a discipline of meditation techniques,
where you adopt various poses and chant mantras in order to seek
some kind of spiritual salvation, e.g. obtain release from bondage
to this illusory, material world and be united with the Brahman
(loosely translated, "Universal Spirit").
(Personally, I would avoid it.)
Weightlifting, on the other hand, is about obtaining a stronger,
bigger, and healthier body.