The upper line of head, neck and shoulders sitting on top of the frame. Its tension comes from the upper back, never from the hands — it is the channel every lead travels through.
The frame is not decoration, it is the wiring: the lead travels as a kinetic chain from the torso through the shoulders into the arms — if the topline collapses, nothing reaches your partner. Two errors dominate. First, hunched-up shoulders: set them up once, then far back and down, shoulder blades flat and lightly together, and leave them there. Second, holding the frame with your arms instead of your upper back — your arms will be shaking within two minutes. What gets missed: “upright” does not mean arched. Two-thirds of standard dancers report lower-back pain, and the road there almost always runs through a topline built from the lower back rather than from core strength. Done properly, the side effect is measurable: an average thoracic kyphosis of 33° versus 39.6° in non-dancers.