These are probably the only form-fitting pants I wouldn't feel uncomfortable seeing people wear in public. Sometimes you'll catch a glimpse of someone in leggings at the grocery store and it gives you the heeby-jeebies, but if they're in a pair of Icebreakers you'll most likely end up tipping your hat to them. And then giving them your coupon for OJ.
Honestly, you'd be doing your lower half a huge favor with Icebreaker leggings. With flat-lock stitching, breathability and ease of motion beyond your wildest dreams, Icebreaker base layer bottoms make all and any of your physical activities a complete and total breeze. Icebreaker Bodyfit leggings are available in full length or legless. The legless ones hit just below the knee.
Icebreaker leggings and base layer pants come in different weights, so there's a pant for any activity and climate. For a lightweight legging, check out the Icebreaker Ultralight or Icebreaker 150 leggings. If you need something a little warmer the Icebreaker 200 leggings are the way to go, with their 200 gram merino wool construction. For a super lightweight but warm baselayer in cold conditions, Icebreaker Bodyfit 260 is the only way to go.
Performance-wise, the road runner comes to mind. Not only would he look adorable in a pair of Icebreaker long underwear pants, but you'll probably run just like him if you have them on. Or was the road runner a girl? No idea. Still fast, either way.