I used to do HIIT years back but stopped for regular cardio (just becuase I enjoy it more). I knew it a bad switch, but as I said I just enjoy long endurance bouts more. The last couple of years Ive made minimal upper body progress and almost no lower. So I decided to go back to sprinting. I started a few days ago and my legs are still shot. I'm sore in places I forgot you could be sore in (particularly the groin). Anyways I'm expecting results from this. I should see results from quitting the prolonged bouts of cardio but am hoping to benefit from the added explosive movement as well. At least it cant hurt.