The new viral challenge is to run 5 kilometres in the smallest space possible - a kitchen, a corridor, an aircraft toilet. On the spot, with no back-and-forth movement. The record-holder is Dom Stroh on TikTok. The clips rack up millions of views. The advice from trainers - do not do it.

Trainer Lety Pellegrín Fernández explains why. When you run on the spot, the movement becomes vertical and repetitive. „You are jumping in place." The same joints get hit 5,000 times - ankle, knee, lower back. Without horizontal movement, the shock absorption disappears. What is left is just impact on the same part of the body, again and again.

It gets worse when the challenge involves unstable surfaces - on top of a fridge, in a bathtub, on a chair. On those surfaces, broken joints and torn ligaments are not rare. Social media is full of „successful 5K" clips and empty of the ones who ended up in A&E.

There is another problem - muscle activation. When you do not move forward and only jump, mostly the hip flexors work - the muscles that lift the front of the thigh. The glutes and the back of the thigh barely take part. The result - pelvic imbalance, a twisted spine, and potential hip pain for months.

The trainer's advice: if you want to run, go outside. If there is no space, first learn proper technique - with targeted strength training, gradually introduce impact, and only then allow yourself running sessions. Without those steps, every „home run" is an investment in pain you will feel months later.

In the end Pellegrín Fernández sends a very clear message. „Chasing attention on social media is no guarantee of health." The Balkans have known that for a long time - here we run on asphalt, not on top of a fridge.