Medicine Ball Crunches
Hold a medicine ball (or dumbbell) and lie flat on your back with knees bent, legs hip-width apart, abs engaged, and arms extended straight up toward the ceiling.
EXHALE: Use your abs to "crunch" up by lifting your head, neck and shoulder blades off the mat. INHALE: Slowly return to the mat to complete one rep.
Keep your shoulders relaxed and your arms extended. Make sure your lower back doesn't arch up from the mat. Only crunch up as high as you can in good form while keeping legs still and feet flat on the floor.
Muscles Worked: Abs