The plank is a popular isometric exercise that works every core muscle, as well as muscles in the back, shoulders, hips, and legs. While most traditional core exercises train the core through movement, the plank trains the core to resist movement by keeping the body stable for a period of time. Known as an anti-core exercise, it builds strength and stability and can improve strength in lifts like squats and bench press. Because there is no spinal flexion involved, planks are a good alternative for those who find ab exercises like sit ups and crunches stressful on the back. Planks can also help to build core strength and master correct engagement to make these exercises easier.