Domain: Healthcare — Human Physiology
Target concept: Achilles Tendon Reflex (Seated)

Video generation prompt: A subject sits on a chair in a relaxed position with the lower leg naturally hanging down. The examiner locates the Achilles tendon above the heel and strikes it once with a reflex hammer. The movement of the foot is recorded from a lateral perspective. The lower leg, ankle joint, Achilles tendon, and the striking action of the reflex hammer are clearly visible. The entire process is performed as a continuous and smooth maneuver.

Evaluation guide:
(i) Target concept: Monosynaptic myotatic reflex elicited by mechanical stretch of the Achilles tendon.
Minimum mechanism: Intact S1–S2 dorsal root ganglia, spinal cord synapse, ventral horn motor neurons, peripheral nerve conduction, neuromuscular junction transmission, and contractile function of gastrocnemius/soleus.
(ii)Storyline: [Frame 1–3] Subject seated, lower leg hanging, tendon exposed and at rest in lateral view. [Frame 4–6] Hammer approaches tendon along smooth arc, maintaining fixed lateral perspective. [Frame 7] Hammer contacts tendon — visible indentation and localized tissue deformation. [Frame 8–10] Immediate plantarflexion of foot begins *only after* contact; ankle rotates while knee/hip remain immobile; tendon recoils; foot returns to baseline without oscillation. Visibility constraint: Entire sequence must be captured from fixed lateral angle with unobstructed view of heel, tendon, ankle joint, and hammer contact zone.

Manual:
Experimental Procedure
1. Subject sits upright on standard chair, hips and knees at ~90°, lower leg hanging freely, foot relaxed.
2. Examiner stands laterally, locates Achilles tendon as vertical cord-like structure 2 cm above heel bone.
3. With reflex hammer, delivers single brisk tap to mid-tendon.
Observation of Experimental Phenomena
Foot exhibits immediate, brief, involuntary plantarflexion (downward flick of forefoot) with no voluntary movement; lower leg remains still; tendon visibly indents then recoils upon strike.
Summary of Experimental Principles
Achilles tendon reflex tests S1–S2 spinal cord integrity via monosynaptic stretch reflex: tap stretches gastrocnemius/soleus muscle spindles → Ia afferent signal → direct synapse in spinal cord → efferent alpha motor neuron activation → rapid plantarflexion.

Prompt Grounding rubric:
level_1: No seated human subject is visible on a chair; the lower leg is not shown hanging down; the Achilles tendon and heel region are absent from the frame; no reflex hammer is present anywhere in the shot; the camera is not positioned at a lateral (side-on) angle to the leg.
level_2: A seated subject and chair are present with the lower leg oriented downward, but at least one setup element is wrong: the Achilles tendon/heel region is occluded or pushed to the frame edge, OR a reflex hammer is visible but not held near the tendon, OR the camera angle is frontal, overhead, or three-quarter rather than a true side-on lateral view of the leg.
level_3: The subject is seated with the lower leg hanging naturally, the Achilles tendon above the heel is clearly visible and centered in a lateral view, and the examiner holds a reflex hammer positioned adjacent to the tendon; chair, subject, hanging leg, tendon/heel region, and hammer are all present together in one coherent lateral scene.
level_4: Everything required for score 3 is present, and the hammer visibly strikes the tendon (a discrete contact moment is shown), the foot's movement only begins after that contact is shown (never before or simultaneous with it), and the whole sequence from hammer approach through strike to the foot's first movement plays as one uninterrupted lateral shot with no cut, camera-angle change, or object jumping to a new position.
level_5: Everything required for score 4 is present, and the lateral framing keeps the heel, Achilles tendon, ankle joint, and hammer contact point unobstructed for the entire sequence (no hand, sleeve, or other object crosses in front of this region at any point), the examiner withdraws the hammer cleanly after the strike so the tendon and heel stay fully visible afterward, and the subject's seated posture and the chair's position remain fixed throughout with no repositioning.

Scientific and Causal Correctness rubric:
level_1: No foot movement follows the strike at all, OR the foot moves upward into dorsiflexion or twists sideways instead of flexing downward, OR the foot moves before the hammer makes contact, OR the hammer swings but never actually touches the tendon.
level_2: The foot moves after contact, but the response is unclear or physiologically off: the direction is ambiguous (not clearly a downward flick of the forefoot), OR the motion visibly originates from the knee or hip rather than the ankle alone, OR the tendon is struck yet the foot fails to move, OR the movement is slow, multi-phase, or sustained rather than the brief single jerk expected of a spinal reflex.
level_3: After the hammer strikes the tendon, the foot produces a single, brief, involuntary downward flick (plantarflexion) of the forefoot with no sign of voluntary correction; the movement is visibly confined to the ankle joint, with the knee and hip staying still throughout.
level_4: Everything required for score 3 holds, and the lower leg shows no pre-strike tension or bracing (it looks fully relaxed right up to impact), the hammer visibly lands on the taut tendon cord roughly 2 cm above the heel bone (the calcaneal insertion), on the midline, rather than on the fleshy calf muscle or directly on the heel bone, and the resulting foot movement is clearly visible to the eye rather than a barely perceptible twitch.
level_5: Everything required for score 4 holds, and the plantarflexion is entirely isolated to the ankle with no visible knee or hip motion at all, the tendon visibly compresses inward at the instant of strike and then springs back outward, showing elastic recoil, the foot settles back to its resting position without extra bounces or overshoot, and there is no sign of the subject voluntarily resisting or bracing (e.g., curling toes, stiffening the leg) before, during, or after the strike.

Spatiotemporal Consistency rubric:
level_1: A severe continuity break is present: the subject or chair vanishes and reappears in a different position between frames, the lower leg's orientation jumps discontinuously (e.g., from hanging to raised) with no visible motion connecting the two states, the reflex hammer jumps to a new location in space between frames, the lighting on the tendon/heel region flips or changes abruptly with no in-scene cause, or the shot cuts or zooms mid-action.
level_2: Moderate continuity problems are present: the heel/tendon/ankle region is blocked from view for more than a few consecutive frames, the shadow falling across the tendon area shifts inconsistently from frame to frame, the lateral viewpoint shows visible warping or parallax mismatch, the leg or foot flickers in and out of visibility, or the hammer's swing is jerky or freezes and then reappears in a different position rather than moving continuously.
level_3: The chair, subject, and hanging lower leg stay in one fixed spatial arrangement throughout; the reflex hammer travels toward the tendon along a single continuous, visible path; the foot's movement begins from rest and follows an anatomically plausible arc; nothing in the scene disappears or jumps position, and the lighting on the heel/tendon area stays consistent with no unexplained flips or bursts.
level_4: Building on score 3, the hammer's swing visibly slows as it nears the tendon and the foot's plantarflexion accelerates then decelerates smoothly rather than snapping instantly to full extension; the skin, heel, and tendon contours do not stretch, warp, or slide out of place; the tendon and heel landmarks stay aligned from one frame to the next with no visible misregistration.
level_5: Building on score 4, the proportions of the heel, ankle, and lower leg stay consistent in every frame; the tendon's visible thickness and contrast remain steady rather than flickering; motion blur never obscures the moment of ankle articulation; the strike-and-response sequence shows no skipped phases (the tendon indenting and the foot moving are both visible in sequence, not jumping straight from contact to full plantarflexion); and the lateral camera alignment does not drift or wobble across the sequence.