The exact time it adds to running is 1.8x. This works when you start your sprint with the Skorpion, MP9, or the USAS 12. You can always switch back to your other gun as long as you started your sprint with one of those three guns. The whole hoax with "The Skorpion must have extended mags" thing is stupid. You don't need any atatchments, just the gun. Also, in the video it says "Unlimited Sprint"... Lol. Wrong. It should be "Run 80% (1.8x) longer". Extreme Conditioning allows you to run twice as long (2x) so if you do the sprint trick with one of the three guns, you'll be able to sprint 2.8x longer. Which is about 20 seconds worth of running.