Domain: Healthcare — Human Physiology
Target concept: Achilles tendon reflex (standing position)

Video generation prompt: A standing subject leans slightly forward with both feet flat on the ground. The examiner stabilizes the subject, locates the Achilles tendon above the heel, and strikes it once with a reflex hammer. The calf and feet are clearly displayed, with emphasis placed on the striking action and the ankle joint at the moment of hammer contact. The overall presentation is simple and follows standard clinical demonstration procedures.

Evaluation guide:
(i) Target concept: Monosynaptic deep tendon reflex elicited at the Achilles tendon in standing position.
Minimum mechanism: Intact S1–S2 spinal segment; functional neuromuscular junction; passive stretch of gastrocnemius-soleus complex must trigger involuntary, synchronous, short-latency plantarflexion without supraspinal modulation.
(ii)Storyline: [Frame 0–2] Subject stands still, then adopts slight forward lean (center of mass shifts anteriorly, knees slightly flexed, feet flat); [Frame 3–4] Examiner positions hands on subject’s upper back/shoulders for stabilization; [Frame 5–6] Examiner visually identifies and targets midline Achilles tendon above heel; [Frame 7] Hammer impacts tendon, single, crisp, vertical contact; [Frame 8–10] Immediate ankle plantarflexion occurs: foot rotates downward around talocrural joint, calf muscle shortens visibly, no ancillary joint motion; all events occur from fixed front-lateral viewpoint ensuring full visibility of feet, ankle, calf, and hammer–tendon interface.

Manual:
Experimental Procedure
1. Subject stands upright, then leans slightly forward with both feet flat on ground.
2. Examiner stands behind, stabilizes subject by placing hands on upper back/shoulders.
3. Examiner locates Achilles tendon directly above heel (midline, taut band between calf and calcaneus).
4. Examiner strikes tendon once with reflex hammer in vertical downward motion.
Observation of Experimental Phenomena
Ankle joint undergoes immediate, isolated plantarflexion: foot moves downward without knee/hip motion; calf muscle visibly contracts synchronously.
Summary of Experimental Principles
Achilles tendon reflex tests S1–S2 spinal cord integrity via monosynaptic stretch reflex: tapping stretches gastrocnemius/soleus → Ia afferent firing → direct synapse on alpha motor neuron → rapid plantarflexion.

Prompt Grounding rubric:
level_1: No standing subject is shown; feet are not flat on the ground; no examiner appears; the Achilles tendon or heel area is not shown; no reflex hammer is visible; no striking action takes place.
level_2: A standing subject with both feet on the ground appears, but either the examiner is missing, or the reflex hammer is missing, or the hammer strikes somewhere other than the Achilles tendon above the heel (for example the calf belly or ankle bone); the striking action itself is missing or not recognizable as a strike.
level_3: A standing subject leaning slightly forward with both feet flat on the ground is shown; an examiner is present and stabilizes the subject with hands on the shoulders or upper back; the Achilles tendon above the heel is visibly targeted; a reflex hammer makes contact with that spot; the ankle and calf stay fully visible; the strike happens after the stabilization, matching the order described in the prompt.
level_4: Everything described in the 3-point level is present, and in addition the strike is a single, clean tap rather than a double-tap, drag, or sustained push; the subject stands still and upright right up until the strike; no unrelated props such as chairs, tables, or on-screen labels appear in the clinical setting; the camera holds a fixed front-lateral framing that keeps both feet, the ankle, the calf, and the hammer-tendon contact point in view together.
level_5: Everything described in the 4-point level is present, and in addition the hammer lands on the midline of the Achilles tendon rather than clearly off to one side, with the tendon visibly taut and continuous from the calf muscle down to the heel bone; the subject's forward lean is visible as a clear forward shift of the head and shoulders relative to the ankles; the clip plays as a single unedited take from start to finish with no visible cuts or frame skips.

Scientific and Causal Correctness rubric:
level_1: No ankle response occurs at all; the calf shows no visible contraction; the foot shows no downward (plantarflexion) motion; or the motion contradicts the expected reflex, such as the foot lifting upward, turning inward, or the knee bending instead of the ankle moving.
level_2: The ankle does move, but not in a way consistent with a fast reflex: the response is clearly delayed (roughly a second or more after the tap), or the foot jerks more than once, or the motion visibly starts at the hip or knee rather than the ankle, or the calf shows no visible contraction even though the foot moves.
level_3: Within the clip, the foot plantarflexes (toes dip toward the floor) shortly after the tap; the motion stays confined to the ankle joint with no visible knee or hip movement; the calf muscle visibly tightens or bulges during the motion; there is no conflicting motion such as the foot lifting or twisting instead of dropping.
level_4: Everything described in the 3-point level is present, and in addition the foot only begins moving after the hammer makes contact, with no movement beforehand; the motion is a single quick downward beat that settles rather than bouncing or oscillating; the calf's visible bulge and the foot's downward motion happen together rather than one clearly before the other; the subject does not appear to consciously resist or correct the movement.
level_5: Everything described in the 4-point level is present, and in addition the foot's downward travel looks like a normal, moderate reflex, visible but not extreme, without the heel lifting off the floor or the whole body swaying; the visible contraction stays in the calf itself, without the thigh or the top of the foot bulging or moving; the tap-to-response timing looks immediate and involuntary, matching a standard clinical Achilles reflex rather than a slow, voluntary foot movement.

Spatiotemporal Consistency rubric:
level_1: Severe continuity break: the subject appears to jump between two different poses with no motion shown in between; a limb (foot, calf, or hand) disappears from view and is simply present again later with no motion connecting the two; the scene's overall lighting suddenly takes on a different character from one moment to the next; the background changes abruptly; the camera view jumps or swings sharply mid-clip; the leg or foot looks structurally broken, such as the foot appearing detached or floating away from the leg.
level_2: Noticeable continuity problems: part of a limb is blocked from view and looks different once it comes back into view; shadows on the subject suddenly point a different way than the rest of the scene, with nothing in the shot explaining why; the overall lighting flickers or dims for no reason tied to the action; the camera drifts noticeably, with a visible tilt or pan that never settles; the calf or ankle region drops out of frame for several consecutive frames in a row.
level_3: The subject stays visible for the whole clip; both feet stay flat on the ground with no floating or sliding; the calf and ankle stay fully in frame throughout; the lighting stays steady with no flicker, pulsing, or sudden color shift; the camera framing does not pan, tilt, or zoom; no body part or the hammer appears to stretch, bend, or warp; every motion (the lean, the strike, the stabilizing hold) follows a plausible physical path.
level_4: Everything described in the 3-point level is present, and in addition the subject's forward lean stays consistent before, during, and right after the strike, without snapping back upright too soon; the examiner's stabilizing hands stay in the same place on the subject's back or shoulders without sliding off or lifting away; the hammer travels toward the tendon along a smooth, direct path rather than wavering, pausing mid-air, or taking an erratic route.
level_5: Everything described in the 4-point level is present, and in addition the motion throughout looks like one continuous, fluid sequence with no visible stutter, repeated frames, or freezing; the hammer, tendon, and background elements keep sensible depth relationships as the camera holds its view, with nothing appearing to pop in front of or behind something it shouldn't; the changing distances (the hammer approaching the tendon, the foot moving relative to the floor) look smooth and continuous rather than jumping between positions.