After six weeks of steady-state cardio 4-6 times a week, I decided to try HIIT. The plan is to do HIIT three times a week. I started Monday. Because of bad knees, I'm using a machine called a Gazelle that has two platforms that swing. I started off with two minutes of "jogging," followed by one minute of "sprinting." I repeated this for 20 minutes. I don't have a heart rate monitor yet, so I don't know if I got my heart rate up enough during the sprints.

Tuesday morning my thighs, the tops, were very painful; as in, hard to walk almost. Is this normal? Was this the result of the sprinting (short bursts of high intensity) or the way I was using my legs? Or both? Should I wait until they're no longer sore before doing another HIIT session? Are they always going to be sore after a HIIT session? Can I not just take a pill and poof--I'm 175 lbs, 9% BF strong, healthy and fit? LOL...of course not; I know that.

it might be normal if you are out of shape. You may want to start doing squats to gain some strenght in your legs. I usually dont get any soreness from sprinting but if I do it is usually in my hams (back of the thigh).