30 mins?
that's more like a warm-up plus a 25 minute run, my friend. how many leg days do you have? HIIT can really tax your legs, so you'll definitely be fatigued the day after, even two days after if you're really pushing yourself. when you're training, something's gotta give. if you do 2 leg days a week plus 2 sessions of HIIT, I would say you can write off the rest of the week completely for legs. if you want to measure your endurance, take at least 2 days off from leg lifts and/or HIIT, preferably 3-4 days, and you should have more endurance for sure. you should be able to run faster too. if this isn't the case, you may be overtraining
and will need more time to fully recover so you can make better progress.
I just love to run, man. The endorphine got me feeling like I'm running on cloud.
Prior to doing the HIIT, I used to do 4 miles in 30mins with no problem on the treadmill (I only use this as a measuring mark BTW, I know it's not exactly precise). After the HIIT, I'm in the low 3mile in the same time frame.
I always run for 30 mins (or when I'm not really feeling it, the elliptical for 30 mins because it's easier on the legs and I go at a low intensity).
Plus I can NOT lift w/o doing some sort of cardio for 30 mins. It's a mind thing I know, just can't get into it. I've been toying with the ideaof replacing running on the treadmill with elliptical and just use the HIIT for running 2 times a week.
Aside from HIIT and running, I work out my legs on Wednesday and Saturday...nothing major, just 3 exercises per day.
Edit: To make things clear because I re read what I wrote and it sounded confusing.
I do HIIT on Monday and Friday afternoon, around the street near my house. I go to the gym in the morning, from Monday-Saturday. Every time I go to the gym,I always do cardio of some sort for half an hour. I don't go running for 30 mins before the HIIT itself.