During the summer I was doing a 5 mile run (my best was 44 min over a hilly course) once a week for tennis and general fitness. After a while I began to look for an alternative. I never felt like I was built for long distance running and my knees began to bother me (they never hurt after tennis). Plus, long distance running was slowing me down on court. I read a little about interval training here on the board and did a quick search on the internet. The idea that a quick workout once or twice a week can boost your cardiovascular capacity and make you faster sounded good to me. I found some tennis specific interval drills that mimic the quick movements needed on court but I figured I'd start by making up my own routine to get a taste of what interval training is like. I have access to a local track and I decided to do the following: 1 lap slow jog 1/2 lap 70% run 1 lap slow jog and then repeat the following 3 times 100 meters at 100% sprint 1 lap mixed slow jog walk then finish with another 100 meter 100% sprint So far I've done this once a week for the last month. This workout literally makes me sick. I never felt so bad in my life - my head starts to throb, I break out in a cold sweat, and I feel like I'm going to vomit (I'm suprised I haven't - I pulled my car over and stuck my head out the window - but nothing came out). Is this the way interval training is supposed to make you feel? I don't think I have any medical problems. Is this the correct way to do interval training? Am I doing too much or am I just in really bad shape and finally pushing myself? On the bright side, I do feel faster on court (this might be psychological or it might be a benefit of no longer running longer distances). Yet, even if interval training does make me faster I don't think I'll keep it up if I have to feel like hell once a week (I'm a wimp).