You should be on pavement with a very slight downward slope. (si.com)
Thousands of acres of pavement for roads and malls and businesses and homes tend to alter the drainage patterns that had evolved for thousands of years. (judithcurry.com)
Your body has to work harder with every step, thanks to the textured, uneven terrain which adds to a super intense, effective workout that's way better than pounding pavement. (myobuddy.com)