The biggest factor determining your destiny on the mat is not the flexibility of your 600 muscles. It's the versatility of eight joints--and the unique shape of the 206 bones responsible for their range of motion.

This kind of understanding and respect for each individual's skeletal limitations are the roots of yin yoga, also called Taoist yoga. The key to the practice is focusing on the connective tissues instead of muscles.  Lengthening these rope-like tissues requires tailored (but not simple) positions and intense stretches held anywhere from 5 to 20 minutes at a time. (When's the last time you spent 10 minutes in Pigeon? Thought so.) Again, yin is not a replacement for yang yoga: Your body needs to both build strength and tame tension, no matter how inflexible it may feel. "The fact that someone bends further than you isn't an indication that they are healthier," Grilley says. "It is only in relation to our own skeleton that we can ask, 'Am I adequately flexible and strong?'"

Philosophically, yin yoga does not send you in search of poster-worthy poses. Instead, it enables you to exercise deep bundles of tension in our eight key joints--ankles, knees, hips, three parts of the back, neck, and shoulders--leading us to one primary goal: increased flexibility, no matter how flexible you are (or aren't). "It's not about whether your shoulder moves 115 degrees or 90 degrees. What's important is that you regularly and routinely take your shoulder through whatever range of motion your bones allow," Grilley says. So, if you feel like a steel rod, that's no excuse to skip yoga. Losing a few degrees of motion might not sound like a lot, but if you have only 20 degrees to begin with, losing half of that will certainly feel like a lot.

To increase energy flow and loosen up, use the following poses from Grilley's Yin Yoga: Guidelines for a Quiet Practice. Work one set of joints daily, or do all of the poses at once. Hold each pose for 3 minutes and work your way up to 20 minutes if possible. You'll likely notice each pose stretches more than just the joint targeted.

If a pose feels painful, or you feel like your bones are blocking movement, skip it or try the suggested modification. Where relevant, the poses are demonstrated two ways: limited joint mobility first, followed by a wider range of motion. And remember: One is not better than another. Stretching, period, is beneficial. Now let's get started.

HIP

These three poses encourage flexion, extension, abduction (like Open Horse, which should free the spine), and adduction (squeezing knees together at chest, for example). All of which means that after a long commute or meeting, you won't walk out hoping the circulation returns in the foot that fell asleep. Not to mention that you're also lowering your chances of a future hip replacement. If you've been on your feet all day, a spinal twist can relieve whole body strain.

Open Horse Stance

While standing, turn feet out in a wide stance. Open legs 3 feet wide. Bend knees deeply until you are in a wide squat. Drop butt back and rest forearms on thighs. Bring weight off your thighs and onto your arms.

Folded Pose

Lying flat on your back, draw your right knee into your chest, clasping both hands at the knee. Switch sides and repeat. Then bring both knees to chest.

Dragonfly

Sit with your legs 90 degrees apart or more. Lean forward. Try to touch hands on the floor in front of you, gradually allowing the elbows--before your cheek follows suit--to rest on the floor.

Spinal twist

Overhead View

Side View

Lie on back, squeezing both knees to chest with ankles together. Cross right leg over left leg and drop both legs to the left, holding top of right thigh with left hand. Draw knees up as close to chest as hip bones allow. Turn head and look right. Repeat on other side.

Have another joint that needs oiled? Pick up the new issue of YogaLife, on newsstands now, for tips on stretching your ankles, knees, back, and shoulders.