What is it that tightens in hind legs when out of work?

[maya2008]

My farrier said, in conversation a while ago, that my retired mare found it so difficult to hold her rear hooves up to be trimmed/picked up because something (a ligament?) tightens in horses that are not being worked. She is now back in light walk work and he was so right - she can now hold her hooves up just fine!

I feel stupid asking him what it was though - does anyone on here know? And can you stretch it without ridden work?

 

[SEL]

Not exactly sure what he's talking about, but my arthritic ones struggle with the farrier down to their joints seizing up more the less work they do. I feed danilon the day before feet trims to help out.

One of mine can get very tight hamstrings, but that's actually in work rather than out of work.

Hopefully someone more clued up than me can help!