Dumbbell Nan Kilo Moteru?
Hibiki is a teenage girl who loves to eat, but when she notices her waistline expanding, she decides to check out the local gym. The gym is full of buff dudes…and Akemi, the student council president?! When Akemi tries to convince Hibiki to take up weight training, Hibiki resists–until she meets pretty boy trainer Machio. Now, Hibiki is willing to do whatever it takes to get fit!
(Source: Seven Seas)
Note: This manga is set in the same universe as Kengan Ashura.