I did a stress test recently, and while my heart is healthy, my stamina is very, very low(expected for somebody who sits as much as I do).
I rarely run, but when I do I can only run for less than 10 minutes, if even that much. For obvious reasons I decided to change that and set a goal for myself, and that is to be able to run a half-marathon (20km) which some of my friends are able to do with relative ease. I'm 22, have low body fat, eat healthy, but not on any strict diet.
In order to have stronger motivation for reaching the goal I need to set the date for it, so my questions are how long will it take to achieve the said goal, how often should I exercise and what is the most efficient way to do it? Thanks in advance