A plank is a simple yet effective exercise that targets the core muscles, including the abdomen, back, and shoulders. To perform a plank, one typically lies face down and then lifts the body off the ground, balancing on the forearms and toes. The body should form a straight line from head to heels, engaging the core to maintain stability. Planks can be modified in various ways to increase or decrease difficulty. For example, a side plank focuses on the oblique muscles, while a forearm plank is a common variation. Regularly incorporating planks into a fitness routine can improve overall strength and posture.