Ditto the other posters.
I have one TWH that is long/lanky and very athletic. Until he was around ten, he burned up calories standing still and I always had trouble "covering" his hip bones. Now that he's 19, sadly he doesn't have that problem anymore; he needs to lose about 50 pounds
The other two have always looked like QH's and both of them have metabolic issues.
Years ago, I was on a trail ride with my eldest TWH, and somebody asked me how I taught that Quarter Horse to gait