A “Six-Pack” does not automatically equal a strong core.
What is the core? Put simply, it is a group of muscles that are in your midsection.
You want a strong core? Then you have to understand the function of the core is to stabilize the spine. You want a strong core? Stop trying to isolate a group of muscles ( sounds ridiculous, doesn’t it?)
In my opinion the best way to develop the ability to stablize the spine is to do movements that:
1. train the correct firing patterns and
2. support weight with full body tension.
One movement that covers both criteria: The Hardstyle, Kalos Sthenos style Get-up