Why do i sweat so much?

its only when im exercising but geez do i sweat and the thing is that im in excllent shape. like a couple weeks ago i was playing one of friends in tennis (he plays D3 in college) and i can usually beat him but the whole time my body is just SOAKED... and i dont even feel tired at all... and its really not all that hot where im at (mid- high 70s)