Warrior III
How to do it
Stand tall, then move the weight onto one foot, spreading it across the big toe, little toe and heel. Keep that leg long with the knee soft rather than locked. Hinge the torso forward from the hip joint and let the other leg lift behind you at the same rate — the two ends of one lever, tipping like a see-saw. Stop when the torso and the lifted leg form a single line roughly parallel to the floor. Turn the lifted hip back down so both hip points face the floor, and flex the lifted foot, pressing back through the heel with the toes pointing down. Gaze at one spot on the floor beneath you. Hands rest at the chest, reach back alongside the body, or extend forward past the ears — hardest last. Hold, then step back to standing and switch sides.
Why it's good for runners
This is the closest thing in yoga to what a running stride actually is: standing on one leg, hinged at the hip, with the pelvis held level by nothing but the glute on that side. The standing leg's hamstring and glute work hard to hold the line, the foot and ankle make constant small corrections underneath, and the deep hip has to stop the free side of the pelvis from dropping. That last job is the one that quietly fails in the back half of a long run, and when it does the knee starts collapsing inward on every footstrike. Held before a run, Warrior III wakes that whole chain up as a contraction, so nothing about it costs you freshness.
Common mistakes
Don't let the lifted hip roll open toward the ceiling — it's the most common fault in the pose and it takes the standing glute straight out of the job. Don't lift the back leg higher than the torso has lowered; that arches the low back and turns a hip hinge into a back extension. And don't lock the standing knee — a soft knee lets the foot and ankle do the balancing, which is the point.