What is the first thing that pops into your mind when you hear the word “exercise”? Hours in the gym—squatting, curling, lunging, and sweating. What if exercise does not have to involve any of these?

A Swedish trainer says you can build muscle using three minutes of this exercise, so we looked at the science.

Ever noticed how tough it feels to hold a plank for just a minute? That is the magic of isometric exercises. They do not need fast movements but still challenge your muscles intensely. These exercises ...