ok but real talk, knees are genuinely one of the most marvellous pieces of biomechanical engineering. They can withstand decades of constant movement, can allow extension (with a lot of force) even when bent 180°, can withstand - and move - hundreds of kg per knee (with enough practice) periodically also for decades, and can comfortably remain with your entire body weight resting on them at any angle from 0 to 180° for any length of time. It's amazing that everyone doesn't have constant knee pain or have their knees simply fail altogether.