What happens to the facet joints during spinal flexion and extension?

During spinal flexion when we bend forward, the facet joints open on both sides between each vertebra. This allows some movement while still limiting excessive stress. As stated in the text, "when we get a lot of that down through the spine, that would be an indicator maybe of excessive opening."

Conversely, during spinal extension when we arch backwards, the facet joints close at a certain point and we get a bony lock that prevents us from bending too far. The text notes that "As we go into extension, these joints close at a certain point and we get a bony lock."

So to summarize, during forward bending flexion, the facet joints open to allow movement but limit too much stress. And during backward bending extension, the facet joints close to create a bony stopping mechanism that protects from going too far into extension. The opening and closing of these joints facilitates spinal movement while protecting from injury.