Puppy
How to do it
Start on hands and knees. Keeping the hips stacked high over the knees, walk the hands forward along the mat and let the chest melt down toward the floor, resting the forehead or the chin on the mat. Keep the arms straight and reaching, with the elbows lifted off the floor. Breathe into the sides of the ribs. Hold, then walk the hands back to come up.
Why it's good for runners
This is the only shape in the method that trains overhead directly. Down dog and the upward salute pass through the position, but neither one stays there long enough to change it. Everything else works the legs, hips and spine — but a kettlebell session spends its time with the bells racked in front of you and locked out above you, and both of those close the front of the shoulders and shorten the lats. Puppy reopens the line from the armpit down the side of the ribs, which is what lets you get overhead without arching the low back to fake the range.
Common mistakes
The one that matters: letting the hips travel back toward the heels. The moment they do, this becomes child's pose and the shoulders stop being stretched. Keep the hips high over the knees the whole time. Don't rest the elbows on the floor either — straight, reaching arms are what makes it work. And back off if you feel pinching at the front of the shoulder rather than length under the arm.