When 17-year-old high school student Jake Harmon told his friends he was going to train only the right side of his body for six months, they thought it was a joke. But 182 days later, the results of his one-sided experiment have shocked not only his classmates, but also fitness trainers and even medical professionals.

The idea started as a personal challenge and a social media stunt. “I wanted to see what would happen if I only worked out one side,” Jake said in a TikTok video that now has over 4 million views. “Like, would I walk crooked? Would I look like a comic book character? I just had to know.”

Armed with a dumbbell, a gym membership, and an unusual sense of determination, Jake committed to training only the right side of his body — that meant right arm, right leg, right chest, and even half of his core. His routine included one-arm curls, single-leg presses, one-arm bench presses, and one-sided planks. He avoided all bilateral exercises and completely neglected his left side.

After 182 days of consistent, targeted training, the difference between the two sides is astonishing. Jake’s right arm now measures over 3 inches larger in circumference than his left. His right leg is visibly more muscular, and even his chest is noticeably uneven. “My shirts fit weird now,” he laughs. “Like one sleeve is tight and the other just hangs.”

But while the results might look funny on the outside, fitness experts say Jake's experiment touches on something deeper: the body's ability to adapt — and the surprising way it compensates.

“What Jake did is extreme, but not entirely unheard of,” says Dr. Kevin Reynolds, a sports physiologist. “There’s actually a phenomenon called the cross-education effect, where training one side of the body can cause strength gains in the untrained side. But visually, the muscles won’t grow the same.”

Dr. Reynolds explains that Jake’s right side has clearly experienced hypertrophy (muscle growth), but his left side may still be stronger than it appears thanks to neural adaptations. “The brain learns movement patterns, and the untrained side can ‘borrow’ that learning. But aesthetically, yes — it creates a very uneven look.”

Jake has documented the entire journey on social media, posting monthly progress photos and funny updates, including videos of him trying to do yoga, run, or ride a bike with his now-lopsided physique. His followers have dubbed him “One-Side Jake,” and many have asked if he’ll start training the other side to balance things out.

“I think I will,” Jake admits. “The experiment was fun, but I don’t want to walk in circles for the rest of my life.”

While Jake insists his body is still functioning well — no injuries or joint pain yet — some physical therapists are more cautious. “Muscle imbalance can lead to posture problems, back pain, or even long-term joint issues,” says physical therapist Angela Kim. “It’s important to maintain symmetry, especially in young people whose bodies are still developing.”

Even so, Jake says he’s proud of what he’s learned — and what he’s taught others. “I didn’t do this to go viral,” he says. “I did it because I was curious. But if it gets people to think differently about fitness, or even laugh a little, that’s a win.”

Now with over half a year of “unilateral gains” under his belt, Jake is already planning his next fitness challenge — though this time, it may involve both sides of his body.