Personally, I think it's in an interesting grey area. Before I played chess, I definitely would have said no, because I associated sports with physical exertion (I was a soccer player). However, when I went to my first chess tournament, I could feel real, physical effects. My heart was beating like crazy, and there was a lot of mental exertion. It's like a mental workout, even though it's not a physical one.
Hope this helps!
