You will gain strength, endurance, balance, and coordination through karate. Muscle bulk? Not so much, although you might see a little bit of definition after awhile. The strength you build will be through simply using the muscles you use in karate. If you were to also life weights, the gained muscle would not necessarily be targeted so as to help you in karate. You need to decide what your goals are. If you simply want to build muscle, you need to lift weights. If you want to do karate, just go to class twice a week (or more, if possible) and focus on getting stronger and better each day.

No striking art by itself will gain you muscle the only way to get that is though resistance eg grappling another person and using strength and skill. I'm a big fan of using the body and other people's body's as well as natural exercises to gain muscle but that takes about 2 hours of continues training to do right and still learn something. Not to say that karate will not teach you grappling but your average class won't. I would look into some wrestling or judo or bjj to go with your karate if your after useable muscle.

45 minute classes? That's crazy! What can you possibly learn in 45 minutes? It takes almost that long just to warm up. Kids classes can be 45 minutes because they don't have the attention span but serious training should be 1 1/2 hour classes. Even my kids classes are 1 hour because I feel if the kids can not pay attention for 1 hour they are not ready to learn a martial art.

I doubt that you can do serious training in that school so I think your results will be accordingly. However if you are training hard then karate can definitely change your muscle tone and it will also condition you but it is not easy training. It definitely changed mine but I did 1 1/2 hours three times a week and more.

Practicing any martial art for a prolong period of time, particularly karate will cause your muscles to develop in some way. One of my good friends has been doing karate for years without lifting weights and he has more defined ab muscles than many athletes from other sports. The kind of muscle you will develop in karate is 'sports specific' muscle which is functional within the domain of karate.

There are academic articles that state that physiological changes occur with Karate. The article I have a link to on my website on the benefits of Karate on men over 50. One of them is states "...Karate training seems to enhance psychologic and social dimensions as well as physiologic performance..."

Sean you are not likely to gain muscle from practicing martial arts. I did so for years you will get other benefits. You can expect it to tone you if you have flab at all but muscle building comes from weight training which some Martial Arts Dojos do have and recommend. Karate or other such arts are not going to make you muscular though. All the UFC fighters if you watch them on TV they train hard at gyms lifting weights. Get some free weights or go to your school gym if you have one.

Yes it really helps you in cardio exercises if you did not stop the karate

I would do some kind of weight training or body weight exercises to supplement your martial arts studies. Have fun! :D

I currently have next to no muscle on me and no fat and I'm signing up for karate which is 2, 45minute lessons a week. Am I going to gain any muscle from doing this? and when will they become noticable?