How to improve heart rate?

I'm 25 , male 155Lb, 180 cm. I am trying to burn some fat by doing a good aerobic workout like the ellipticals (cross trainer). I cant do jogging because I have a knee injury (ACL).

Now the machine tells me I need to keep my heart rate at 127-135 for effective fat burn. I cant keep it at this level for more than 10 minutes..it goes up to atleast 160 at 60 RPM that is. I can keep it at 130 tops if I keep the RPM at 45 or lower but then the cal per hour is very low and that would mean longer workout

So I figured ok , I got to improve my heart rate so even at 60 RPM it should be under 130, so I have now been doing the cardio workout and working out with my heart rate at 150-170 or so.

How how long will it take before I see an improvement in my heart rate.1 month.2 months..or more.?

I know a lot depends on my body type , food habbits etc..I'm in pretty good shape..trying to shed off those last bits of fat from the abdominal area to get those perfect abs

Thanks in Adv

don't rely on that machine; it uses a "standard" table of pule rates etc and nobdody will match it.

generally, interval training is the trick to do what you want to do - which means go "hard n fast" for 30 seconds or a minute or two, then recover, then repeat.

the machine probably has an intervals program. or you can do it manually.

but... fat burning is a different goal than improving your pulse at a given setting. the idea of a "fat burning" zone is very popular in the fitness world, but it's been oversimplified so much that even most trainers have an incorrect understanding.

you will burn calories no matter what kind of exercise you do. it you exercise more intensely, you will burn more calories.

whether those calories burned cause your fat to melt away is determined by many other factors, like diet, when you eat before and after exercise, and of course your total calories eaten.

if you want to lose fat, just eat right, exercise, and give it time. the last few bits of flab are the hardest.

When i started aerobics i had to start out slow if my heart raced i just slowed down and continued at a slower pace till my heart beat was OK. i kept doing exercise and my body got use to it as time went on. As time went by i could increase the time and amount of strength when doing aerobics