This video clip shows two variations of the push-up, a traditional core
exercise still very much used in current core programming. Both
variations, unstable lower, complex and arms elevated, pike complex,
can be made easier (the higher the incline the easier the challenge) or
more difficult (the farther away from the axis the load is placed on the
lever arm, the more challenging an exercise will be).
See more push-up variations and over 300 exercises in Conditioning to the Core (Human Kinetics 2015).