I made a vow to be more adventurous this year, so I’m signing up for all the weird and wonderful workouts I can find in my hometown of London, then reporting back on what I’ve learned about fitness, ...

If you’ve ever held a plank, paused at the bottom of a squat or pressed your palms together in front of your chest, you’ve done an isometric exercise. Ta-da! These holds might look simple — after all, ...