Half Saddle
How to do it
Kneel on the floor. Extend the right leg straight out in front. The left knee stays bent under you, top of the left foot on the floor, sitting back toward (but not necessarily on) the left heel. Lean back on the hands first. If that's comfortable, lower to the forearms. If that's comfortable, lower the back to the floor. Most runners stop at the forearms. Hold and breathe, then switch sides.
Why it's good for runners
The left-leg quad and hip flexor are exactly the tissues running tightens — and Half Saddle stretches them both at once, on one side, while keeping the right leg out of the way. Doing it asymmetrically lets the tighter side actually get released without being limited by the other. This is the most direct quad-and-hip-flexor opener in the catalog.
Common mistakes
Don't push past sharp knee pain — the front of the kneeling knee gets loaded here, and runners with cranky knees often need to skip this pose or stay propped high on the hands. Don't crank your way down to the floor if the quad won't allow it; the forearms are a perfectly good stopping point. And if the top of the ankle complains, fold a blanket under it.