Ok so Im 15 and I am asian and I try to run for 1 km (actually im not sure how many km but it took me 30 mins and I run on an average speed) my PE teacher says I won't have a big legs but a tone one...I mean according to a Thai girl in my country we are very petite and small but I dunno if I keep running will I have a big ugly legs?????

I'd think being female, unless you're genetically gifted, or chemically enhanced it's very hard to gain bulk/size. Plus running I think doesn't lend itself to bigger muscles - if that were true all the runners you see would have huge legs and tiny upper bodies.

no, running wont bulk up your legs. So dont worry about that.

OK thank u for ure answer ^_^!! if u dun mind I wanna know what is a good side sit-up???

Most runners have long lean legs. I think a good oblique workout is side planks resting on the elbow.

lol you most likely ran further than 1km if you ran for 30minutes unless you were crawling and took a 5 minute break

Yup...5K = 3mi / 10k = 6mi

A decent 5K would be around 20min. If you are running longer distances then your legs will be sure to stay lean.

If you start out with super thin legs they might build up a little, but running certainly isn't going to make them bulky

I would think if you are concerned about bulky legs then you would be concerned about a wide waste. If so then training obliques directly is not something you want to do.

Wide waist? can u explain more about that? and if Oblique make u have a wide wasit than what excersie should I do?

You're 15 years old: you should be focused on developing a solid structure and healthy attitude towards exercise and diet, not misguided concepts of "big ugly legs" and "getting your sides lean." You have an opportunity that I didn't have when I was 15: learning proper exercise and weight management, not wasted time and effort on poor exercise, habits and focus with easily accessible information.

Look through the stickies, read and learn, and lift heavy and with purpose of form and function, not "what your friends tell you."

Running doesn't make your legs big and bulky.

My ex-girlfriend was a cross country runner and she had hott legs let me tell you.

Tell your PE teacher to look up the words "toning" and "muscle tone".