Dumbbell Nan Kilo Moteru?

Synopsis

At the gym, Hibiki weighs herself and notices that she still gained weight. She asks Machio for advice to lose weight. Akemi tells Hibiki to try the Lat Pulldown Machine. After using it, they visit the gym's bar and Akemi offers Hibiki more protein. The next day, Akemi convinces Hibiki to go to the swimming pool to get some exercise. Later, at Ayaka's house, Hibiki and Ayaka are watching a movie. Just as they are about watch more movies, Ayaka's sister asks her to help her out and bring Hibiki along too. To Hibiki's surprise, she finds out that Ayaka's family owns a boxing gym called the Glory Gym. Ayaka's sister reveals that their dad taught them how to box and they serve as the coaches when he isn't there. When Ayaka stops to rest for a moment, Hibiki notices her physique and asks about how she works out. Ayaka tells her about some of the exercises that she does. Afterwards, Ayaka's sister suggests that Hibiki should try the punching bag. When she punches it, the bag breaks.

(Source: Wikipedia)