I've been doing resistance training for the last 3 years, while mostly slacking off on the cardio side of things. Overall the training hasn't really helped my cardio problems in all this time.

I was checking my heart rate the other day. While sitting it's around 90, standing is 100 and walking is 110. Last time I checked it on waking it was 85. Doing something as simple as climbing stairs will leave me slightly out of breath. Also, I've been a chronic asthmatic since I was 7 so my lung capacity is pretty shot at the best of times. My asthma got really bad in march this year, but I'm just managing to maintain with increased strength meds. Does anyone know if a lifetime's worth of medication would have contributed toward this problem?

I decided to go running a few days back and discovered I can't really put too much effort in without my heart rate soaring. So what I ended up doing was running at a fair speed for 30s and then doing a fast walk for 1min30. For my heart this pretty much equates to HIIT, but not the muscles. During the walk it would drop to around 140 and running would peak it around 180.

My question is this, is what I explain above a good way to increase my cardio fitness? I'm going to go get a proper set of running shoes fitted tomorrow as I want to try do this 3x a week for around 30 mins a session. One thing to mention is that where I live it's extremely hilly (many inclines sharper than the highest setting on a treadmill), so speed varies a lot; this is also the reason I can't cycle, as it's too difficult to regulate my heart rate.

HIIT is really the best thing you can do to improve your cardio fitness. However, if you can do it for 30 mins then I wouldn't personally count it as HIIT, more as just regular interval training. During your high intensity sets you should be putting in an all-out effort: if you can go harder, then you're not pushing yourself enough. Start out with 30 seconds of sprinting as fast as you can, followed by 90 seconds to 120 seconds of walking. Repeat that for 10-15 minutes. As your cardiovascular fitness improves, reduce the recovery periods.

HIIT is not about heart rate at all. It's about perceived effort. You don't need to watch your heart rate at all really (unless you're just curious).