The name is both a description and a warning. Hard Core is an forearm-plank-based core workout built entirely around position and disruption - everything happens from the plank, and every exercise is designed to make maintaining that position progressively harder. Plank leg raises, body saw, up-and-down planks, and three closing 10-count holds make up the full session.

Plank leg raises isolate one side of the posterior chain at a time: glute and lower back on the working side, full core brace on the stabilizing side to prevent the hip from tilting as the leg lifts. Body saw - a forward-and-back shift of the entire body over the forearms - is a long-lever anti-extension drill that loads the deep stabilizers, particularly the transverse abdominis, far more than a static hold does because the lever arm changes throughout the movement. Up-and-down planks - transitioning between forearm and high plank - add dynamic shoulder girdle demand while the core has to stay rigid through the positional change, requiring the serratus anterior and rotator cuff to work in coordination with the abs. The three closing holds are not decoration: they arrive after all of the above, making the final isometric challenge significantly harder than it would be cold.

Keep the hips level throughout the leg raises - any rotation in the pelvis means the obliques have already given up and the lower back is compensating. On body saw, the movement should be long and controlled; short, choppy saws reduce the lever arm and take away most of the exercise's value.

The core isn't a six-pack. It's everything holding you together when everything else wants to fall apart.

Make it harder: Extend all holds to 20 counts and add a push-up between each up-and-down plank transition at the top position.

Make it easier: Perform leg raises and body saw from a high plank position instead of forearms, and reduce holds to 5 counts.