I've had mine for 30 years--bought one again in my early 20's LOL because I've always enjoyed hula-hooping sp? for fun.
I have to flex, tighten my abs, etc. to keep it going around so I do feel it in my entire core area. I don't know if constant use strengthens the area, I think it would. Again, I hula hoop merely for fun.
I'd love to know if others use it for exercise; I assume they're en vogue again?
I have a weighted hula hoop on my wish list because I loved using them as a youngster (I had a hula hoop with a "bee" in it so it buzzed as I used it) and a few years ago tried one that a coworker had. I do not doubt it helps with strength and flexibility but also with coordination. The coworker who had me try it was amazed at how I could quickly change from one direction to another and walk while doing it. I'm thinking there is a certain amount of brain usage that goes into it that you may not normally use (if that makes any sense). Of course the fun factor is always a plus.