I'm new to running. I was originally working toward long distance running until I recently learned about interval running. I did my first workout today and loved it. The thing is, I also love long distance running eventhough my "long distance run" is 3-4 miles of continous running. I'm alternating my interval workouts, running on Monday, Wednesday, and Friday. In between, I work on my upper body, do yoga, and work on my core. My aim is to feel and look fit. My question is, because I'm doing interval running and workouts in between, do I stop doing continous running? I really enjoy it but my main focus at the moment is to get fit and interval running seems to have a better effect.
If I can still do continous running, do I run on the same day I do interval running or on my workout days?
Were it that I was coaching you I would tell you to do the exact opposite of what you're wanting to do. Why? The core systems of the human body require time to develop, and difference systems develop at different rates. While the cardio-vascular systems and the muscular system develop at a relatively rapid rate, the skeletal, joints, and connective tissue (ligaments and tendons) infrastructure develop at a very slow relative rate. By engaging in speed drills of any type (intervals are by definition a speed drill) before you've built a good solid base of Long Slow Distance (LSD) miles, getting injured is not so much a matter of "If", but "When".
Once again, were I coaching you, I would recommend you log at least 600 LSD miles before gradually incorporating intervals, ladders, fartlek, repeats, or any other faster paced workouts into your weekly routine.
Disclaimer: there are exceptions to every rule, and there are a few (very few) "special" individuals out there who can start right off with speed drills and never seem to get injured; that said, I've yet to meet one such individual in the flesh.
Are you talking about High Intensity Interval Training (HIIT)? The objective of HIIT is quite different from distance running. There are varying opinions on which is more effective for general fitness. It is possible for the two to complement each other but I woldn't recommend doing them on the same day. Also, as shipo mentioned, the potential for injury is higher with HIIT, which imposes high, sudden loads on muscles, tendons, ligaments and joints. Be sure to fully warm up before doing HIIT.