Planks are the MacGyver of bodyweight movements: They’re super tough and great for almost any situation. The versatile move is best known for working your core, but planks also engage more than 20 muscles, including your shoulders, back, arms, legs, and glutes. Even better, planks allow you to work your core without the risks of back injury and overstressed hip flexors that come with traditional sit-ups.

Source: 47 Crazy-Fun Plank Variations for a Killer Core | Greatist