Usually when I do HIIT, my heart rate is sitting around 180-190 bpm, and I've even registered around 200bpm at times.
Obviously, that isn't a good idea for you. But, in your situation, I would probably keep on doing what you're doing, and slowly increase your heart rate from week to week. Say, shoot for 155bpm for a few weeks, and push yourself a little harder after that, perhaps to 160bpm. Make sure you check with your doctor though; I have a healthy heart, so its no problem for me to max it out as much as possible. But I had to start slow too.
How hard do you go with your elliptical? And what is your diet like? The 100lb loss is simply fabulous, but as you're almost certainly aware, you have to adopt a pretty good diet, and eat healthy to avoid gaining most of that weight back.
IIRC, you were eating at a pretty low calorie total last time we talked about this, so I assume you're off of it. The best option would probably be to figure out your BMR - basic metabolic rate - making sure you include the amount of exercise you do everyday. Find out what this is, and slowly bring up your calorie amount each day, until you're 500-1000 short of that.
Here is a site that calculates it for you.
http://www.tlbc.ca/blog/index.php/bmr-calculator/
I'm at 2300, resting, meaning that is what my body would burn if I lay in bed all day. Add my activity level in, and suddenly I'm up around 3600. So, I'd have to eat around 3000 calories in order to lose 1 lb per week, and around 2500 to lose 2 lbs per week.
Once you have that figured out, adjust accordingly, but make sure you 'slowly' bring yourself to that level. Meaning if you're eating 1000 calories right now, 'slowly'....even if it takes you a month, bring yourself up to 2500(if that is what it'll take to lose at a rate you're happy with). Reason for this is because your metabolism has adjusted itself based on the diet that has lost you 100lbs. You'll slowly want to adjust it back to a different level.
Exercise is beneficial....diet is fundamental. Weight lifting would be an added bonus; muscle burns more calories at a rested state than fat does, and for someone who is overweight, you can burn fat for energy to gain muscle.....which helps immensely because you won't have to eat at a calorie surplus in order to create that muscle.
I'm going to post 2 different links to different threads that explain weight loss, and diet better than I ever could.
Here:
http://forums.johnstonefitness.com/s...ad.php?t=19229
And here:
http://forums.johnstonefitness.com/s...ead.php?t=1222
Both of them have helped me completely change my life. Bookmark them, or even sign up on the forum if you have other questions. And read them often.
Also
www.fitday.com is a online resource that helps you track calories eaten, and calories burnt. Check it out....pretty simple to use, and motivating for someone starting out.
Hope this helps you out.
Oh, I wouldn't recommend watching the scale, or weighing yourself more than every 2 weeks. Keeping tabs on your body fat is a much better idea, and I have a home test spreadsheet that I can send you, where you basically input the measurements from all over your body, and it gives you a pretty accurate result. Within 1-2% for sure.
Here is a link in regards to scale watching...
http://www.primusweb.com/fitnesspart...ight/scale.htm