So you've built your core to the point that your horse hill climbers (mountain climbers) feel effortless with high rep ranges? Well add 2 sliders under your feet and have a go.
Core sliders are two-sided discs which can be used to challenge body awareness, control, stability, strength training and cardiovascular endurance. If used correctly, they REALLY engage your core
When used under your feet, you will increase the time under tension with your feet remaining on the floor surface (through the sliders) longer. Your core will thank you - after its finished burning 😉