Ok, I have a question about running.
the first question, your welcome!
Is it safe to jog on asphalt or is it bad for my joints? I'm not overweight.
that questions can be answered by your shoes!
when you go buying running shoes, the first question you should be faced with is, where do want to go jogging?
if the surface is rather smooth (forest trail) your shoes should be underdamping. the exact opposite should be for running on asphalt, there you need much more damping!
considering you as an ectomorph, that should not be the problems for your joints, just use good damping shoes.
There might be a more serious problem for your joints (separated from the surface your running on), if you tend to supination or pronation, i.e. your foot tend to roll to the inside or outside. you should consider a qualified seller for further advice! Using the wrong shoes could increase a supination or pronation!
How long should I prepare to be able to run 42.2km?
that questions can't be answerd spontaneously.
it depends on your instant capablities, so for that i should have more information ;-)
I love running but I don't want to lose weight (if I lose 5 more kg I'll be underweight 
), how should I do it? I try to eat often and as much as I can take but now matter how much I eat I'm can't gain weight. ;]
), how should I do it? I try to eat often and as much as I can take but now matter how much I eat I'm can't gain weight. ;]don't say those things to loud, there might be jealous people out there ;-)
generally you can reduce that problem (as losing weight as well) to a simple calcualtion (ok very simplyfied):
your body need energy for every days life as well as for extracurricular sports and activity. the way you gain this energy is eating and drinking. you lose weight if you eat/drink less then you need and vice versa.
the fact, that you love running implies that your extracurricular activity is very high and that might be hard for you to eat that much. more interessting might be your basal metabolism rate (BMR), that might help to qualify your special underweightborder! once there was a compareable case, a teenager joining a more professional soccerteam, which made him and his parents take care of a healthy nutrition. it doesn't take long for this boy complaining about doziness and weakness and so on. the simple explanation after a MD consultation was that his BMR is exceptional high! this boy was able to eat everything an as much as he wishes to without any limitations.
doing a spirometry might verify that, so that your personal underweight can be defined. methods like BMI, Caliper or other formulas for evaluating your weight always relays on a model, there will always be people that doesn't match that models ;-)
an MD can resolve exactly if 5kg less will be a risk for your health, and thats the point it depends on, not some tables with lots of numbers that say who is underweight or overweight.
Or should I wait a few years till my metabolism starts changing (I'm young and I'm an ectomorph)
this answer is associated with the risk for your health discribed above.
i hope that could be of any help for you!
