fast walk or jog

[irish bulldog]

ive started my first day of cardio,i did about three miles jogging at a low speed,i see people do cardio for 45min+ which is what im aiming for but my three miles only lasted 20 mins and i couldnt do anymore but i know im not fit,my legs were sore and lungs very sore does this mean it is too intense for fat burning.
i need to get a hr monitor which will give me a better idea but is it better to power walk?and should you be out of breath and tired after it cardio for fat burning,thanks

[bluethunder]

If you are only doing 20 minutes thats fine until you get condition & lung capacity increases. If you did that on empty stomach and had high intensity 20 min is okay , remember if it is done 4-5 days a week it adds up. Power walking is good as a warmup but not too good for burning the calories unless it is a long time. Just my 2cents

[irish bulldog]

ok bro thanks for the info

[ImmmtheIceman]

Definitely do cardio on an empty stomach..much better results.