In my (NSH) opinion, weight training should be a part of any half-way serious Martial Artist's training.
Whether you're into competitions, or just training to be able to kick just a little bit more ass than the next guy.
For 3 important reasons...
1. Hit harder.
2. Move faster.
3. Hit harder. (Which is important enough to be included twice)
For about the last year and a bit, I've been weight training pretty seriously, although I've trained on and off for over 8 years.
At the start of this, I decided that I wanted to train mainly for increased strength, rather than to get bigger, as I thought that an increase in mass might be more of a hindrance in Karate.
Since then, I've only really put on 3-5 pounds, but I've got stronger, am moving noticeably faster and hitting with more power.
If you'd like to see this put in a more scientific, and probably more convincing way, follow this link.
There's a few things you need to do before you set off on this voyage of discovery.
Examples of crap advice that you will be given.
"lifting heavy weights'll make you too big" - Oh really? Just try it then, and see how bloody easy it is to get 'too' big.
"do 20+ reps with a light weight to develop speed" - This just doesnt follow. Speed depends on a lot of factors, one of which is how strong you are.
20+ reps does not make you any stronger.
"you shouldnt do squats, it's bad for your back/knees. Do leg presses instead" - Squats are only bad for your back or knees if a problem already exists there, or if you are doing them badly.
They are an essential excercise for ANYONE training with weights for a sport.
Some leg press machines can actually be worse for your knees and back.
"you shouldn't do deadlifts, they are bad for your back" - This is said by people who are feart of deadlifts.
As long as you're doing them properly, they are great.
Do a heavy set of deadlifts and you'll get an object lesson in channeling aggression.
I've enjoyed doing this crap advice section so much, I'm going to add to it periodically.
Basics
As I said, the 3 things you should build your weight training routine round should be the Squat, Deadlift and the Bench Press.
That's because, with these 3 movements, you can train your entire body with a relatively high weight, which is the key to strength training.
Also, these excercises are relatively easy to learn, when compared to the Olympic lifts, which are another good option for strength training.
But, as I've said before, it's absolutely critical that you get coaching on these lifts by someone who knows them.
The Squat.
Squats rule.
They should be the most important excercise in your routine, as they'll give you the most benefit.
Done properly, Squats work all of your legs, with emphasis on the thighs and glutes. It also strengthens your lower back.
Aside from this, it helps develop a raftload of supporting muscles, used to help stabilise the bar and balance yourself with the weight on your shoulders.
Theres a bit of a debate ongoing about whether you should squat either above, to or below parallel.
Personally speaking, I'm firmly in the 'squat deep' camp.
Basically, I think squatting deep uses more of the range of motion of your knee joint, which, if done properly, can only be healthy.
There was a (very long) thread on uk.rec.bodybuilding recently which covered this very topic.
I've posted a response from one of the regulars, George UK, that explains the benefits of the full squat very well, and more importantly, backs it up with research.
To get to it, follow this link.
The Deadlift.
Deadlifts are my personal favourite, purely because it's a scary looking, brutal lift, in which you can lift a shed-load of weight.
Once again, though, learn the proper form for these, cos there's no surer back wrecker when done badly.
With deadlifts (DLs), you squat down in front of the bar, getting your hips as low as possible.
With your back straight, and your eyes looking straight ahead, you simultaneously push upwards with your legs and pull your torso to vertical.
Deadlifts are another excellent whole body excercise, hitting the legs, entire back, especially the lower back, arms and grip.
The Bench Press.
This is another favourite of mine, which is arguably one of the best excercises for developing upper body strength.
Aside from ensuring that you do this properly (which should go without saying by now) you have to be careful with this one if your'e working out alone.
Failing at the bottom with a 200 pound barbell sitting on your chest, with no-one to lift it off is not an experience I'd recommend.
That's the 'why' covered.
I hope I've been convincing.
At some point in the near future, I might even cover the 'how'.