If you are 14-years-old and want to gain weight so you can train for martial arts how can you gain weight without build-ups?

If you are 14-years-old and want to gain weight so you can train for martial arts how can you gain weight without build-ups?
In a moment I'll answer this question, but I honestly think you've asked the wrong quesiton : Let me show you what I mean:I've trained extensively in Kendo and to a lesser degree in Judo and Aikido. During the time I trained, I had the opportunity to meet and speak with a huge number of martial artists and especially teachers -- sensei's in my form. And every one answered this question the same way:Each one said that you modify your own approach to the art to take advantage of your strengths and your body type. Some of the animal forms work very well for one body type, and not at all for another, so, if your ryu includes animal forms, consider letting your technique lead you to forms that will focus on your strengths, instead of changing your body type.I'm 5'11" and about 210lbs. When I was practicing martial arts I was in excellent shape (not so good now, darn it!). My sensei was 5'4" and perhaps 145lbs. I used a Bear for, which allowed me to use my mass as a weapon. He used a combination of forms, with tiger and snake being a large part of it. You'd think that I sould have been able to simply pick him up and carry him around for a while: but the truth of it was, in spite of his size, I never once was able to lay a glove on him or even control the match.If you're smaller than I, you can change direction faster than I -- it's simple Newtonian physics. Sparring with me then, you'd avoid my driect moves, go at an angle to my direction, and strike vulnerable spots. My sensei would agree that there's no reason you can't win with that approach.If you must gain weight, the best way is to train -- roadwork, gym and dojo -- and then eat a balanced meal in quantities proportional to your calorie burn. As you build muscle, your weight will automatically increase. You'd be wise to have a chat with a licensed nutritionist about this too.