Niall Horan was blazin' in the sun Friday during a very hot afternoon jog.
The former One Direction singer stripped down -- partially -- during a jog in the place celebs love to be seen exercising -- Runyon Canyon in L.A.
Niall's gotta be feeling good about himself ... his song, "Slow Hands" has soared like the L.A. PM temp.
If you're thinkin' of coming to L.A. and you want some exercise ... Runyon's got all shapes and sizes -- it's super fun.