Every summer brings a new fitness trend that "everyone is doing", and this year it's the so-called Norwegian method - short but brutally intense intervals popularised by celebrities like Elsa Pataky. The question rarely asked: does it actually work, or is it just another fashionable label?

The method is simple on paper: four intervals of four minutes each, at an effort of 85 to 95 percent of maximum, with three minutes of rest between them. Add a warm-up and cool-down, and the whole session lasts about 40 minutes. The idea is for the body to work in the "golden zone" where the biggest adaptations happen, without overloading to exhaustion.

Trainer Nerea Povedano explains that the whole logic revolves around lactate - a substance the body produces under effort. "Lactate was wrongly linked to fatigue, but now we know it's an important source of energy," she says. The method, according to her, boosts cardiovascular capacity and metabolic efficiency, but it comes with one important limitation.

And that limitation is precisely the thing the fitness industry rarely flags: this is not for beginners. Povedano says plainly that the method is meant for people with some sporting experience and a good base, not for those just getting up off the couch. For weight loss it can help, but only as part of a balanced programme with strength training. In other words, there's no magic trick - only hard work in a neat package, which is exactly why trends like this come and go, while the real result always demands the same thing: persistence.