Knee Hyperextension
The knee travels behind the plumb line and locks past neutral in standing.
What this describes
Hyperextension is the knee resting behind the line from hip to ankle instead of on it. It is read as an angle in a side photo, not as a feeling: most people with a substantial hyperextension angle do not feel it at all. The companion readings are the end-point of a seated knee extension and what the joint does at the top of a heel raise, because a knee that locks harder under load is the pattern worth recording.
Three-grade thresholds
| Grade | Threshold |
|---|---|
| Within range | Hip–knee–ankle within 3° of a straight line; heel raise ends with the knee still on the line. |
| Borderline | Knee sits 4–8° behind the line, or the standing angle increases by more than 3° at the top of a heel raise. |
| Deviated | More than 8° behind the line, a visible backward bow from the side, or a heel raise that ends with the knee locked hard and the calf unable to control the descent. |
Self-screens for Knee Hyperextension on this site
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Heel Raise Lock Check
Rise onto the balls of the feet and watch what the knee does at the top. The same joint that rests past neutral while standing often locks harder the moment the calf works.
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Side Photo Knee Angle
One relaxed frame and one extended frame, taken from knee height on a marked spot. The difference between the two is what separates a joint that rests past neutral from one that cannot reach it.