Core Strength is a popular fitness buzz word in spite it's exact definition being somewhat ambiguous. While a multitude of torso muscles are involved, I simply define (and assess) 'core' strength, in a functional context, as the ability to effectively transfer force between the arms and legs. Therefore, 'core' strength is assessed indirectly with movements that require the transfer of force from the ground (or other surface) through the body. The exact muscular demands will vary based on the movement and amount of force output.
The Turkish Get-Up:
The Turkish Get-Up is a full-body, multiple-plane exercise that can be used to assess and develop full-body strength, including 'core' strength and joint stability. It can be described as moving your body from a lying position, to a standing position, back to a lying position while holding a weight in one hand (both sides are assessed or trained independently). As simple and common the movement is, it illuminates deficiencies in movement effficiency. These deficiencies can be the result of a combination of a lack of joint mobility, joint stability, body control, and muscular strength. Since the Turkish Get-Up is a dynamic exercise, the muscular strength and stabilizing demands continually change as one moves through the exercise. Additionally, the external resistance (weight held in one hand) can be modified to more effectively discriminate strength and stablilty levels.