Start on all fours. Extend your right arm in front of you and your left leg behind, actively reaching in opposite directions.

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, ...

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, ...