Episode 4 of "Pump Up the Healthy Love" kicks off with an intriguing twist as Hyeon-joong declares that Rosa's gym duties are no longer required. Instead, he challenges her to step up and prove her worth by entering a bodybuilding competition. This declaration ignites a fierce determination in Rosa, leading her to embark on an intense training regimen.
Elsewhere, Mi-ran finds herself at the gym but is abruptly interrupted by a text message that sends her rushing back home. The reason for her haste? Her mother, Lee Sook-im, is about to arrive. In a panic, Mi-ran, Ji-ran, and Ji-ran's boyfriend Kang Dan scramble to clean up the house, with Kang Dan ultimately hiding in the closet to avoid detection. As Sook-im arrives and inspects the premises, she declares her satisfaction. However, her satisfaction is short-lived as she expresses her desire to meet Joon-seok, Mi-ran's ex-boyfriend. Mi-ran, desperate to keep the break-up a secret, quickly agrees to set up a meeting and then makes a swift exit.
Back at the gym, Hyeon-joong takes center stage, coaching Rosa on how to pose for the competition with confidence and elegance. He then whisks her away to a tanning salon, where they unexpectedly encounter Lee Roy, who is also training a competitor for the same event. During their casual conversation, Lee Roy reveals that he has changed his name from Bong-won to Roy, adding a touch of mystery to his character.
With nowhere else to go, Mi-ran finds herself back at the gym. When Hyeon-joong arrives and prepares to disrobe, Mi-ran, embarrassed and unsure of what to do, hides herself away. Mistaking her presence for a ghost, Hyeon-joong is spooked and flees the gym in a panic. Taking advantage of his absence, Mi-ran sneaks into Hyeon-joong's room and starts snooping around, curious about his personal life.
The next day brings another challenge for Rosa. She receives a call from Nabbi Korea, the organizers of the competition, requesting confirmation of her age due to her being older than the other contestants. This call sets the stage for a heated argument with Hyeon-joong over her lifting capabilities, which ends abruptly when a weight falls on her foot. Frustrated and in pain, Rosa decides to withdraw from the competition.
At work, Mi-ran prepares for dinner with her mother, a ritual of shared warmth and sustenance. Suddenly, Sook-im's call interrupts the quiet anticipation, requesting that Mi-ran invite Joon-seok along. To facilitate this unplanned gathering, Mi-ran's boss, Joon-bae, chivalrously diverts Joon-seok's attention, allowing Mi-ran to subtly whisk her mother away. Mi-ran crafts a makeshift excuse, claiming Joon-seok is out of town, but Ji-ran, unwittingly, spills the beans about their breakup. Mi-ran confesses that Joon-seok's reluctance to share intimacy deepened her wounds, only to have Sook-im criticize her for not shedding pounds. Hurt by her mother's dissatisfaction, Mi-ran storms out of the restaurant, leaving behind shattered expectations.
Seeking solace, Mi-ran finds herself at a fried chicken joint. Just as she's about to indulge, Hyeon-joong joins her, using the greasy delight as a penalty for allowing Rosa to come to harm. Mistaking soju for water, he inadvertently gets tipsy, leading to a series of playful, albeit drunken, antics. With some effort, Mi-ran guides the now-intoxicated Hyeon-joong back to the gym, where an astonishing revelation awaits them, though its nature remains hidden from our view.
The following morning, Hyeon-joong and Mi-ran forcibly escort a disgruntled Rosa and Alex into a taxi, bound for the competition venue. Rosa, understandably upset, learns that Hyeon-joong and Mi-ran had witnessed her workout sessions. Far from injured, her foot had been fine, and she had been training diligently. Hyeon-joong, ever the encourager, urges her to participate.
The competition unfolds swiftly. When Rosa's turn arrives, she strides out to thunderous applause, posing confidently even after the music ceases. Rosa secures a participation trophy, a modest prize that ignites her passion for competing further.
Returning home, Mi-ran discovers Sook-im has prepared a meal, a gesture of reconciliation. Sook-im attempts to mend fences, urging Mi-ran not to be discouraged. Mi-ran responds by showing her a picture of Rosa, expressing her desire to embody such vigor and strength. Sook-im disagrees, insisting that no man would prefer such a physique, but Mi-ran asserts that wanting to look like Rosa is validation enough for her.
Meanwhile, Ji-ran and Kang Dan, adorned in bold punk attire, stood in anticipation outside the office, awaiting the arrival of Joon-seok. When he finally emerged, they confronted him with stern warnings, insisting that he never again address Mi-ran with disrespect.
Inside the gym, a festive atmosphere enveloped the room as everyone rejoiced over Rosa's advancement to the finals. Amid the celebrations, a gym member shared an intriguing tidbit with Mi-ran, revealing that Hyeon-joong had once been smitten with love. The fourth episode of "Pump Up the Healthy Love" concluded on a whimsical note, with a young boy entering the gym and innocently calling Hyeon-joong "Daddy."
In the epilogue, a tender scene unfolded as Hyeon-joong and Mi-ran dozed off at the gym, oblivious to the world around them while Rosa vigorously worked out. After Rosa's departure, Mi-ran stirred, intending to leave. However, Hyeon-joong gently held her back, playfully preventing her from sneaking a sweet Yokan bar he had thoughtfully purchased for Rosa.
