When a force is exhirted on your core it is felt throughout the entire body, just as a spiderweb responds to a touch on a single strand. Though it will not be as powerful or concentrated as where the initial force was made, the movement does affect the rest of the body. by strengthening the real core - which is, for us, the posterior chain - you will create a tangible impact in the movement of all the surrounding tissues, including your extremities.