Dumbbell Nan Kilo Moteru?
Sakura Hibiki is your average high school girl, with a voracious appetite. Noticing her clothes tightening in lieu of her slowly expanding waistline she decides to look into enrolling in the nearby gym. There she runs into a girl from her grade named Souryuuin Akemi.
Akemi, who has a muscle fetish tries to get Hibiki to enroll in the gym despite its high ratio of macho men. Thankfully a beautiful trainer, Machio, appears and unknowingly convinces her to enroll and start her quest to a great body.
(Source: MU, edited)