You may be able to hold a regular plank—but can your core keep you stable when your body is loaded from one side? That is where the side plank becomes especially valuable. Running, golfing, skiing, cycling, lifting, and field sports rarely challenge your body in a perfectly symmetrical position. One leg accepts your weight. Your torso rotates. Your arms and legs generate force in different directions. Your core must keep your spine and pelvis controlled through all of it. Sid