Spiderman Plank

The spiderman plank takes a standard plank and adds a knee drive toward the elbow on the same side, which turns a purely isometric hold into a movement the obliques have to produce. The plank position still demands everything it normally does, holding a straight line from head to heels against gravity, but now one leg leaves the floor on every repetition and the trunk has to stay level while it does. That combination of holding and moving is closer to how the core actually works than either a plank or a crunch on its own. The tell that the exercise has stopped working is the hips rising. As the knee comes forward it is tempting to pike upward to make room, which releases the tension the plank was creating. Keep the hips low and let the knee travel as far as the position allows.