Chair
How to do it
Stand with the feet together or hip-width apart, whichever is steadier. Bend the knees and send the hips back and down, as though lowering onto a seat set behind you. The weight rides in the heels — you should be able to lift the toes and still balance. Let the tailbone drop so the low back stays long, keep the ribs over the hips, and reach both arms forward and up alongside the ears, palms facing each other. Shoulders slide down away from the ears. Hold, breathing steadily, then press through the heels to stand.
Why it's good for runners
Chair is a held squat you do standing up, and it asks the quads, glutes and calves to work in the range a run is about to use, without any impact and without a single rep. Coming before a run, that matters more than the stretch: a held contraction wakes those muscles up and gets blood into them, which is what a warm-up is actually for. The ankle position is a quiet bonus — sitting back with the heels down loads the ankle into dorsiflexion under bodyweight, the range that lets you roll through a footstrike instead of falling off the front of it.
Common mistakes
Don't let the weight drift into the toes and the heels lift — that turns it into a knee-forward squat and takes the glutes out. Don't arch the low back to keep the chest up; drop the tailbone first and let the chest be wherever that allows. And don't chase depth — a shallow Chair with a long spine beats a deep one held together by the low back.