I have really tight hips and lower back. There was a time three burpees would send me to the chiropractor whining that my hip was trying to kill me. I sprained my hip sometime in the past once or maybe twice while falling on ice or falling off a horse. I am not sure which. I told my chiropractor he should just pick one because I was not sure which of many falls did it. Thanks to my excellent chiropractor and greater attention to mobility and flexibility training I can now do things like burpees and mountain climbers. But some days my hip mobility still really sucks. I have been working on being able to get all the way down for a full squat with good form. I find the absolute bottom tough to reach although I am much closer than I use to be.
I found the following article on bodybuilding.com that makes suggestions on how to work on reaching a full squat (ass to ankles). The best part about these suggestions is that no equipment is required.
How to perform a full squat and reap the benefits: