I want to do muscle strengthening exercise. I heard that you need a certain amount of carbs to build muscle tissue. Is that true and how many carb per day. Can I stay low carb and still build muscle strength?

Yes, you need carbs to build muscles efficiently, but if you don't mind slower progress, you can build muscle even on low levels of carbs.

How much depends to a large extent on your muscle mass. It's very individual. Even adding 25-40g of dextrose around my workouts allows me to build muscle at a reasonably fast pace.

Even on induction levels of carbs, though, I added 6lbs. of LBM while losing 4lbs. overall, over the course of 9 or 10 months doing barely any exercise. The high-protein supports muscle development and maintenance on its own--and don't forget that your body can convert protein to carbs if it has to.

This is a very good question, and not so straight forward to answer. I will try to answer as clearly as possible.

Strictly speaking, for your body to grow muscle you DO NOT need carbs. However that is only a part of the story...

First.
In order to grow muscle you need to stimulate the muscle fiber (e.g. weight training), and have progressive stimulation, meaning you need to be able to train at a consistent or improving level. If you are on reduced carbs (under 100) this can be a very difficult thing to do. Many weight lifters report that their performance is quite hampered by LCing (can't lift the weight today they could lift a few days ago). So their training is not progressive.
This means the muscle is not getting the total stimulation to grow that it needs, leading to reduced gains.


Second.
Being in ketosis is a catabolic environment. That means the body is in a breakdown or losing environment. To gain optimum muscle mass an anabolic environment is needed, a gaining and growth environment. So LCing and ketosis is not optimum for muscle gain.

That said, in a little over a year period I have gained about 8-10lbs muscle mass on 20 carbs a day. Doing a total of about 10 carb-ups in that time period.

If your goal is to be a pro Bodybuilder LC is a hard, slow way to get there. But if you don't mind slower growth LC will work OK.

JWJ

Just an addendum to jwjpilot's (great post, BTW) and my posts:

If you're new to resistance training, you'll progress faster because there's more improvement to be made, kind of like you lose weight faster when you've got more to lose.

People in good shape already progress more slowly, and those who got into good shape on relatively high carb levels are going to have a period of adjustment before they start making any gains at all.

On CKD, though, over the course of 8 weeks I lost (and bear in mind I'm a little person) over 2% BF and gained a couple of lbs. of LBM. That's just 2 months, on a little person. Larger people (read: regular-sized ) tend to change faster!

Patience, my dear, patience. Slow and steady and all that.

you also get the advantage of beginner gains - that is, as you begin weight training your nervous system gets better at recruiting the muscle that you do have - so you'll see pretty good strength gains w/out any gain in muscle - at least for the first few weeks. But because you are working more of the muscle that you have (doing more work with it) you now get the full calorie burn benefit of the muscle you do have.