PivLock refers to the way you swap lenses in these new shades from Smith: Just flip the earpiece skyward and it snaps free at the temple so you can go from clear to dark in seconds. The PivLock is ideal for runners: It's super lightweight; the field of view is endless; and the hydroleophobic-coated, carbonic TLT lenses are tough to break (and easy to clean).  Also, the nosepiece has three different settings to lock it down tightly on your face so there's no annoying shaking and jiggling when you're in a flat sprint or scrambling on a mountain trail (shaking and jiggling being reserved for the podium dance). [$159; smithoptics.com]