Mighty Morphin Muscle Girl Warriors (Patreon)

In 1993, upstart TV cable network Fox Kids launched a low-budget tokusatsu show featuring three girls gifted with superpowers, and super-muscle, by an alien benefactor, to fight the invading hordes of Hortense Horribilis. The alien recruiter picks three highly intelligent, nerdy library science majors from a nearby state college to fight for Earth against Horribilis and her minions. In the first episode they are poorly equipped to deal with the menace, but over time the alien benefactor's technology transforms them into powerful warriors of impressively muscular stature.

The pilot for the show was filmed with three actresses who'd never been given Boomgirl, and were each physically average. While the plot specified that they were treated with "Megaboomer", a substance that had the physical benefits of  Boomgirl but also bestowed superhuman strength and other gifts, each of the actresses was treated with Boomgirl after the filming of the pilot. Over the first two seasons, viewers got to watch the characters grow into powerfully muscled warriors. 

Sequences involving the giant Amazord incarnation of the three lead characters were borrowed from a Japanese TV series with a similar theme, 超人司書 筋肉少女忍者 [Superhuman Librarian Muscle Girl Ninjas].

The series continued on for over 15 years, with a new cast being brought in every one to two years to take on the mantle of the initial three fighters. Each time the young actresses were treated with Boomgirl and their slow muscle growth transformation was used as part of the plotline.