Prior framing (since 2026-04): the cup is a head-position cue. If the head lifts, the cup falls. The cue trains "looking at the finish" (water line at forehead, eyes to the wall behind).
1. The cue now has a biomechanical justification, not just a behavioural feedback loop. "Keep the head back because the cup stays on" is a closed loop (cup → cue). "Keep the head back because it flattens the body, and a flat body reduces drag" is an open loop (cue → mechanism → outcome). For athletes who want to understand why, the open-loop framing is the durable one. 2. The carryover to swim-backstroke is clearer. A swimmer who learns the head-back cue still has to learn to flatten the body off the cue. A swimmer who learns the head-back = flat-body = drag reduction chain has the whole outcome in the loop from the start. 3. The cup-cue's failure mode becomes diagnostic. "Cup stays on but body still sinks" → the issue isn't the head, it's somewhere downstream in the chain (hips, knees, kick).
The cup + three BK kick variations (streamline / alignment on back / rotation kick) has been the Carter program pattern since 2026-04 (see Cup On Head Backstroke Head Cue). The 2026-07-01 Wed session is the first time the cue has been linked to the chain: head → body → drag.
2026-07-01 framing: the cup trains head position because head position controls body position, and body position controls drag. The cup isn't the goal. A flat body is the goal. The cup is the lever.
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