Fast heart rate & calories burned

So I'm pretty out of shape. Even just walking at 3.3 mph with a 1% incline my heart rate gets up to 150 BPM max. How am I supposed to keep my heart rate in my target heart rate zone if by just walking, it goes above it? Also, if I stay in my target heart rate zone, it doesn't feel like i'm doing anything.

As for calories burned, my heart rate monitor says I burned 614 KC by exercising at 3.3mph for 35 minutes, but MFP says I burned 235 or so. Which value do I trust?

Thanks

The best thing to do would be to see a doctor and get a stress test. When I started using a heart rate monitor I was alarmed because my heart rate was off the charts when I exerted myself and when I stayed in what the "fat-burning zone" I couldn't break a sweat. It turns out that women often have higher heart rates because they have smaller hearts. My heart rate also recovered very quickly after I stopped, which was a good sign. I ultimately had a stress test, which was normal. I've never been overweight; I'm not sure that a heavier person should just push himself if he has doubts. Maybe you could do a combination of endurance cardio, like walking, and HIIT.

I ignore all calorie estimates on exercise equipment and HRMs. They're usually not accurate. Besides, I look to calorie reduction for most weight loss. If you're creating a good calorie deficit and working out consistently, you'll lose weight.

As you indicated, your heartrate is high walking because your aerobic fitness is poor. You are doing the right thing to improve it. For right now I wouldn't be overly concerned with the heartrate. It will come down as your fitness improves. For the long term, the best way to improve aerobic fitness is to exercise for long durations at around 75% max heartrate. For you, this would be around 157 bpm. Right now you are there walking. Pretty soon you will have to run to get your heartrate that high.

Aerobic condition improves slowly but it can continue to improve for years. Because of the specific physiological changes induced by the exercise you should see some improvement every 3 to 6 weeks. The more you exercise within your current capacity the faster improvements will occur.

Just to give you some idea of what kind of improvements can occur with dedicated and correct training, I am 53 years old and have been doing a lot of running for 2 years. Right now when walking outside at around 3 mph my heartrate is usually between 60 and 65. That is lower than my resting heartrate was when I started.

So, you're doing great. Keep it up and the improvements will come.