The great yoga teacher B.K.S. Iyengar performed planklike yoga poses of extraordinary difficulty, balancing prone on his hands alone, with or without a leg folded beneath his body. These arm balances are out of reach for all but the most advanced yogis. However, less esoteric plank variations will provide a considerable challenge, even if you're extremely fit. The hardest variations call for both strength and balance.
Hardest Front Plank
The hardest front plank is the so-called atomic push-up, and it requires suspension-training equipment. Lie on your stomach and slip your feet into the footholds directly under the suspension device's anchor in the ceiling. Place your hands just outside your upper ribs, with your palms facing forward and your elbows tucked in next to your body rather than splayed to the sides. Engage your core, legs and glutes. Straighten your arms and press into a high plank, keeping your back straight. Your body should be parallel to the floor. Next, move your knees toward your chest and allow your hips to rise up over your shoulders. Return to plank position, then lower slowly to the floor.
Hardest Side Plank
The most difficult side plank variation will challenge your core, especially the hard-to-reach muscles on the side of your torso and flank such as the gluteus medius and obliques. To start, lie on your side with one leg stacked directly on top of the other. Bend your lower arm and rest on your forearm, keeping the elbow directly below your shoulder. Bend your bottom leg until your knee is even with your hip. Engage your core muscles, then lift up off the floor until your body forms a straight line. Keep your bottom leg bent and raised along with your body, maintaining a 90-degree angle with your knee. Gently lower to the starting position.
If you're flexible and strong, other challenging plank variations may be within reach. Upward plank pose requires shoulder flexibility as well as core strength. Sit on the floor with your hands several inches behind you and facing forward, your legs bent and your feet on the floor. Press your hips up until your torso is straight and parallel to the floor. Carefully straighten your legs one at a time and keep your hips high. To exit, slowly lower your hips to the floor.
Side Plank Variation
This side plank variation requires less strength than the side plank with bent lower leg, but it calls for great lower-body flexibility. To start, perform an ordinary side plank with straight arms, balancing on your hand. Bend your upper leg and grab your big toe between the first two fingers and the thumb of your upper hand. Straighten the leg and extend it to the sky, keeping hold of your toe. To exit the pose, gently release your toe, return your leg to the starting position and lower your body to the ground.