Wow, you can sprint for 2 minutes straight?
I'd use the HIIT on your off days from the gym and only if your diet is right. Tread HIIT like a weight training session nutritionally speaking.
A good guideline to follow is a 3:1 ratio of rest to "sprinting". I usually do mine on a exercise bike and will go all out for 15 seconds then pedal at a slower pace for 45 seconds to let my heart rate get closer to normal.