Domain: Engineering — Biomedical Engineering
Target concept: EMG signal

Video generation prompt: On the electromyography (EMG) acquisition platform, surface EMG electrodes were placed on the surface of the biceps brachii muscle. The subject was instructed to slowly flex the elbow and maintain different angles (30°, 60°, 90°). EMG signals were then acquired and displayed in real time on a screen, with the amplitude of the EMG waveform marked in red.

Evaluation guide:
(i) Target concept: Real-time electromyographic response to graded voluntary muscle contraction.
Minimum mechanism: Surface electrodes must be in direct, stable contact with electrically active tissue; muscle fiber depolarization must generate time-varying potential differences detectable as oscillating voltage; mechanical joint angle change must drive proportional neural drive and thus EMG amplitude modulation; red visual encoding must be bound to the signal"s vertical dynamic range.
(ii)Storyline: Frame 1–2: Stable wide shot showing EMG platform, subject"s arm at rest, biceps surface visible, electrodes already placed. Frame 3–5: Smooth elbow flexion initiating from ~0°, progressing through identifiable intermediate posture (~30°), then ~60°, then ~90°, all within continuous motion under fixed viewpoint. Frame 4–8: Waveform screen enters view (or is already present) and displays evolving oscillatory signal; amplitude envelope widens progressively with each angle increment. Frame 5–10: Red marking appears as a thin, saturated red outline strictly bounded by the top and bottom extremes of the waveform oscillation, scaling vertically in exact synchrony with amplitude growth, never extending to time axis, baseline, or noise floor. No cut, no zoom, no repositioning: all elements co-located and co-evolving in a single continuous take.

Manual:
Experimental Procedure
1. Place surface EMG electrodes on biceps brachii muscle surface.
2. Instruct subject to slowly flex elbow through 30°, 60°, and 90° angles.
3. Display real-time EMG waveform on screen with amplitude marked in red.
Observation of Experimental Phenomena
- Electrodes remain fixed on biceps surface throughout.
- Elbow angle progresses visibly and continuously across three distinct positions.
- Waveform amplitude increases with elbow flexion angle.
- Red marking appears exclusively on waveform amplitude envelope.
Summary of Experimental Principles
- Surface EMG detects electrical activity from skeletal muscle fibers.
- Biceps brachii activation increases with elbow flexion torque demand.
- Amplitude of raw EMG correlates with motor unit recruitment level.

Prompt Grounding rubric:
level_1: No EMG platform is shown; the biceps region is never visible; no electrodes are placed on the skin; the elbow never flexes; no waveform screen appears; and no red marking is used anywhere on the screen.
level_2: The EMG platform or the biceps region appears, but at least one required piece is missing: electrodes are never shown on the biceps skin, the elbow never visibly flexes, no real-time waveform screen appears, or red is never used to mark the waveform.
level_3: The EMG platform, the biceps with electrodes attached, the flexing elbow, the waveform screen, and red marking on the waveform are all present in the same scene, but the order is off, e.g. the electrodes appear only after flexion has started, or red marking is visible before any waveform is shown.
level_4: Electrodes are visibly attached to the biceps before flexion begins and stay on the skin throughout; the elbow flexes through three visually distinct stages progressing from a small to a larger bend; the waveform screen is present and shows a continuously updating trace for the whole clip; red marking sits on the waveform region rather than on unrelated parts of the screen; at most one small flaw occurs, such as the red line briefly flickering or a short hand occlusion of the electrodes.
level_5: Electrodes are shown placed only on the biceps skin, not slipping onto the tendon or nearby bone, and remain fixed there for the entire clip; the elbow shows an unbroken, continuous flexion through three clearly distinguishable joint angles; the waveform screen displays a continuously changing trace throughout; red marking sits on the waveform's amplitude region rather than on the axis, labels, or background for as long as it is visible; the platform, biceps, electrodes, screen, and marker are all visible together in the same fixed shot without disappearing or being occluded.

Scientific and Causal Correctness rubric:
level_1: The waveform shows no relationship to the elbow's motion, for example it stays flat while the elbow flexes, or the red marking sits on parts of the screen unrelated to the waveform's amplitude, such as a label or the background.
level_2: The waveform changes as the elbow flexes but in the wrong direction, for example amplitude shrinks as the angle increases or the trace is busiest at rest, or red marking is placed on an arbitrary screen element rather than tracking the waveform's height.
level_3: Waveform amplitude visibly grows as the elbow angle increases from the smallest to the largest bend, matching the expected rise in muscle activation; red marking sits on the waveform itself, but it covers the whole trace line rather than just the top-to-bottom span of the oscillation, or it stays a fixed height even as the amplitude visibly changes.
level_4: Waveform amplitude increases step by step as the elbow angle increases across the three flexion stages; red marking tracks only the top-to-bottom span of the waveform's oscillation and widens as the amplitude grows, but the red marking disappears briefly during one of the angle transitions, or its color visibly fades during the highest-amplitude stage.
level_5: Waveform amplitude rises visibly and consistently at each successive elbow angle, matching expected muscle recruitment; red marking stays confined to the waveform's peak-to-peak span at every moment it is shown, its height tracking the amplitude change with no visible pause, gap, or fading, and no appearance on unrelated screen regions; the marking's behavior stays tied to the muscle's activation level throughout.

Spatiotemporal Consistency rubric:
level_1: Electrodes jump from one location to another between frames, the elbow's angle changes with no visible motion in between, the waveform screen abruptly changes size or orientation, or the lighting on the arm changes drastically from one moment to the next.
level_2: The electrodes visibly slide to a different spot on the skin without any repositioning action, the waveform screen tilts or shifts position on its own, or the red marking pops on or off the screen with no fade or motion leading into it.
level_3: Electrodes stay in the same place relative to the skin's surface features; the elbow's flexion looks like one smooth, continuous motion rather than a series of jumps; the waveform screen stays still and undistorted; the red marking stays attached to the waveform rather than drifting off it, but there is one brief, noticeable stutter, such as a short camera wobble in the background or a moment where a hand partly blocks the electrodes before moving away.
level_4: There is no jump in electrode position, no screen warping, and no sudden lighting change anywhere in the clip; electrodes keep the same position and angle on the biceps throughout; the elbow's flexion looks anatomically smooth with no sudden speed changes; the waveform screen stays rigidly fixed in place; the red marking's vertical extent moves only in step with visible amplitude changes, without any separate, unrelated jitter of its own.
level_5: Electrodes show no visible slipping or drift on the biceps at any point; the elbow's flexion is fluid and continuous with no skipped frames or unnatural speed changes; the waveform screen shows no warping, no shift in position, and no flicker in brightness; the red marking's appearance, growth, and shrinkage track the waveform's shape smoothly, without any visible stutter, overshoot, or lag that a viewer would notice.