[@LeeRoy] Gah, of all the things I meticulously checked over, I forgot her starting baseline... Blythe starts at roughly 100 tons lifting capacity, and every strength increase from that point forward is directly measured against the forces leveled against her, i.e. if someone attacks her with 200 tons of force, Blythe's strength increases to match that attack, for however long it is measured against her. The instant increases in strength are temporary, for Blythe to permanently increase her strength she needs to work out like anyone else, but that would entail having a powerful force measured against her constantly and repeatedly while she works up her new baseline to match it. 
In other words, an infinite increase would require constant and ever increasing amounts of force, constantly applied over days, if not weeks or months.