The "core" is often used in relation to the abdominal muscles. However, the core is the entire trunk of the body - all muscles excluding the musculature of the limbs. The function of the core is to stabilise the body. So, to challenge and strengthen the core, sit-ups are not going to do it. What we need to focus on is compound exercises which put the body in an unstable environment - in doing so, the core will have to engage in order to stabilise the body and control the movement. This program has 4 sessions per week focusing on these unstable compound lifts in order to build core strength and stability. You may notice that the program includes many overhead exercises - this is because overhead exercises are fantastic at challenging the core. You'll also notice that there are no specific "ab" exercises - remember, we are focusing on the entirety of the core and not just a specific muscle of the core. The sessions will challenge the whole body and within a few weeks of the program you should be feeling more stable and strong. As you work your way through the 4 weeks, you need to think about pushing the intensity a bit by adding more load - if we fail to do this, the body may not optimally change. Challenge brings about change.