What is it? You know how much you hate planks? A mountain climber is basically a plank where you run on the spot. I know, right? Fun.

How much does it cost? Nothing. You could drop to the floor right now and do some if you wanted. You won’t, obviously, because that sounds hellish. But you could.

What does it promise? A great explosive bodyweight exercise, mountain climbers help to strengthen your abs and lower body, while simultaneously giving you a decent cardio workout.

What’s it actually like? First, here’s how you do a mountain climber: you get into the plank position and, without letting your foot touch the ground, draw your knee up to your chest. Return it and repeat with the other knee. Do this over and over again as fast as you can in bursts of about 30 seconds or more. Keep your hips low, like you do for a plank.

If that sounds awful, that’s because it is awful. It wears you out, it hurts your arms and it looks like the stupidest thing ever invented. As part of a circuit class, though, it fits in nicely with star jumps and burpees. Just don’t get good at them, because next comes sliding mountain climbers. This is where you keep your feet on the ground at all times, sliding with your socks or on upturned carpet squares, and that’s even more awful than the regular version.

Best and worst bits Unless you count your eventual uptick in basic fitness, mountain climbers have no best bits. The worst bit, though, is when you attempt to do them tired. Your technique will go to the wall and they may end up doing more harm than good.

Is it worth it? Painfully so.