Start: Assume a plank position: forearms and hands on mat, body lifted, holding body weight between arms and toes. Do not lock knees. Keep abs pulled toward spine, shoulders down and back, and head in line with spine. Avoid arching back, lifting butt, or dropping hips to one side.
Move: Lift right leg out to right side, and touch floor with toe. Bring leg back to center, then move left leg out to left side. This equals one rep.
Repeat: Perform two sets of six to eight reps with one minute of rest between sets.