Seated Fold
How to do it
Sit on the floor with the legs straight out in front of you, feet roughly hip width apart. If your pelvis tips backward as soon as you sit down, sit up on the edge of a cushion or a folded blanket. Bend the knees as much as you need — for most runners that is more than they expect. Fold forward over the legs, letting the spine round completely and the head hang. Rest the hands wherever they land. Then stop working and stay.
Why it's good for runners
This is the whole back line in one shape: the soles of the feet, the calves, the hamstrings, the low back and the long muscles either side of the spine, all lengthened at the same time. That matters, because they are one chain and they tighten together. Chasing them one at a time is the battle nobody wins — tight hamstrings arrive with a tight low back and tight calves because they are not three problems.
An hour of running locks that whole chain long and tight, and the five-breath fold in a normal routine is a maintenance dose. Three minutes is a different thing entirely. Muscle lengthens and springs back within seconds; it takes minutes before the connective tissue underneath starts to answer, and that tissue is what decides how much range you keep.
Common mistakes
Don't force a flat back. Every other fold in this method is a flat-back fold and this one is deliberately not — an athlete drilled on the halfway lift will fight the roundness for three minutes and get nothing. Don't pull on the feet; the hands rest, they never haul. Don't keep the knees locked straight out of stubbornness, which just moves the load to the back of the knee where it does not belong. And don't keep adjusting — the depth you arrive at in the first ten seconds is not the depth you finish in, provided you leave it alone.