Copenhagen Plank

Prop your top leg on a bench with your knee straight, resting on the inside of your shin or ankle, and stack your forearm on the floor beneath your shoulder. Lift your hips and your bottom leg off the floor so your body forms a straight line supported by just that forearm and the propped leg. Your top inner thigh, pressed against the bench, is doing most of the work holding you up here — that's the piece a standard side plank doesn't touch. Keep your hips square and lifted rather than letting the bottom hip sag toward the floor.