Weighted Plank

Set up in a standard forearm plank, elbows under your shoulders, body in a straight line from head to heels, with a weighted belt around your hips carrying the load. Brace hard through your core before you settle into position — the added weight makes it much easier to let your hips sag the moment you get tired. Keep your glutes and abs squeezed the whole time rather than resting into your lower back to hold the weight up. If your hips start dropping or your lower back rounds to compensate, that's the point to stop rather than grinding through extra time in a bad position.