I started doing stair sprints this week in my building. I managed to do 16 floors x3 within 10 minutes (From 2nd to 19th, since there is no 4th, 13th, and 14th floor......crazy asians). I got one word to describe the experience..........BRUTAL!!!! I then followed up with a crossfit style work out consisting of three 6 minute circuits. 20 seconds on, 10 seconds off for 6 minutes alternating between two different exercises. Each circuit contains 2 different exercises and one of them is always legs. Finished off with a 10 minute jog or run, depending on how your legs feel.