Pump Up the Healthy Love Episode 4 begins with Hyeon-joong abruptly removing Rosa from her gym responsibilities. Instead, he instructs her to prove herself by entering a bodybuilding competition, prompting her to begin intense training. Meanwhile, Mi-ran receives a sudden text and rushes home—her mother, Lee Sook-im, is arriving unannounced. Mi-ran, her sister Ji-ran, and Ji-ran’s boyfriend Kang Dan scramble to clean the house, even hiding Kang Dan in the closet. Once Sook-im approves of the home, she demands to meet Mi-ran’s boyfriend, Joon-seok. Mi-ran stops Ji-ran from revealing their breakup and quickly makes an excuse to leave.

Back at the gym, Hyeon-joong starts teaching Rosa how to pose for the competition. He also takes her to a tanning salon, where they encounter Lee Roy, formerly Bong-won, who is coaching another competitor. Mi-ran, having nowhere else to go, ends up at the gym and hides when Hyeon-joong arrives. Mistaking her for a ghost, he flees. Mi-ran then snoops around his room while he’s gone.

Later, Rosa gets a call from Nabbi Korea to verify her age, being older than the average contestant. A heated disagreement with Hyeon-joong about her lifting capacity ends with her injuring her foot and declaring she’s out of the competition. Meanwhile, Mi-ran prepares for a family dinner, only to learn her mother expects Joon-seok to join. Her boss Joon-bae distracts Joon-seok so Mi-ran can manage the situation, but Ji-ran accidentally reveals the breakup. Mi-ran explains that Joon-seok refused intimacy, prompting Sook-im to criticize her weight. Frustrated, Mi-ran walks out, upset that even her own mother finds her lacking.

She ends up at a fried chicken place where Hyeon-joong joins her, punishing himself for Rosa’s injury by eating greasy food. Mistaking soju for water, he ends up drunk. After some chaotic drunken antics, Mi-ran hauls him back to the gym. There, they both witness something shocking—though the audience isn’t shown what it is.

The following morning, they drag a bewildered Rosa and Alex into a cab and head to the competition venue. Rosa is furious, but Hyeon-joong reveals they saw her secretly exercising—she never injured her foot. Encouraged, Rosa decides to compete. When her moment comes, Rosa confidently performs her routine, continuing to pose even after the music stops. She wins a participation award, which sparks her motivation to keep pursuing bodybuilding.

Back at home, Mi-ran finds that her mother has cooked dinner. Sook-im tries to make amends and tells Mi-ran not to give up. Mi-ran then shows her a photo of Rosa, expressing her wish to be like her. Sook-im dismisses it, saying no man would be attracted to such a physique. Mi-ran firmly responds that wanting it for herself is reason enough.

Meanwhile, Ji-ran and Kang Dan dress in punk outfits and ambush Joon-seok outside his office, warning him never to treat Mi-ran disrespectfully again. At the gym, everyone gathers to celebrate Rosa reaching the finals. A fellow member reveals to Mi-ran that Hyeon-joong was once in love. The episode closes with a young boy entering the gym, calling out to Hyeon-joong as “Daddy.”

In the epilogue, Rosa works out while Mi-ran and Hyeon-joong are asleep at the gym. After Rosa leaves, Mi-ran attempts to sneak off with one of the sweet Yokan bars meant for Rosa. Hyeon-joong stops her by pulling her in close.