However, good muscle can enable us to run in a good shape easier, which let runners continue their races with less effort and prevent us form injury. Especially, for cross country runners and trail runners in the mountains, good inner muscle is essential to keep your balance even on the dirty unpaved road.
So, here is how to improve your muscle.
First, as I mentioned before a little bit, inner muscle is very important to keep you body balance while you run. Apparently, you use only your legs to run, but actually, we can say we run with your upper body. You never need to strenghthen it like a lift up athlete because heavy upper body can damage your legs. (Muscle is rather heavy. It's three times as heavy as fat in the same volume!!) But appropriate inner muscle can decrease the damage to legs and you'll have less chance to get injured or falling down during your race.
I recommend you to do core training for your upper body. For beginners, first, fall prone to the floor, and try to keep your body in the air except your arms and feet. Your body should make one line, so not to put your butt too high or too low. Your abs should hurt. You'll keep this form for about 40 seconds and do it twice or three times.
Also, you should train your muscle on the side. You lie on one of your sides and try to put your body in the air except one arm and foot. Make your body a line again, and do this training on both sides.
You won't need strong shoulders for running, but waving your arms in the appropriate form can enhance your performance. You'd better improve your shoulders to achieve it, not arms themselves because you'll use the conjunction of your body to move your body as well.
Prepare dembbells which weighs 1~2 kg each. Have them in your hands, and keep your arms parallel to the ground. It'll be tougher training than you think. Keep this form for 30~40 seconds, and do this exercise twice.
And don't forget your legs training of course! Squat is a well known training, however, wrong squat can cause knee injury, which is difficult to cure. When you squat, try to bend your knee in the same direction as your toes. It prevents you from twist your conjunctions of your knees.
Biking and daily running will be good, too. And strong calves will absorb the damage to your legs. Repeating putting your heels up and down is the best way to strengthen your calves. You can do this exercise even on the train.
I hope you'll be a good runner by having a good training and an appropriate rest.
