pie`n`mash said:
throwing a sandbag builds functional strength for...yes throwing a sandbag, a sandbag is no way similar to MMA, yeh it might help a little but it`ll never substitute grappling training or boxing training, sandbag training is just a strongman thing that somehow found its way into the MMA community coz some company wanted something they could sell at a super marked up price. The fact is that if you train in MMA you need to get used to throwing a person around, a sandbag doesnt try and escape when you try and slam it or try and knee you in the solar plexus when you try a takedown on it.
Sorry guy, but I'll try to explain it as best as I can. Mind you I will be paraphrasing what was said by someone much more knowledgable then me (James Smith).
Here's why you train with heavy weights in what may not be a perfectly "sport specific" motion:
Let's take bombing people as an example. True enough that the best way to practice this is to do it on people. I can't fight that. However, you can strengthen the needed muscles more effectively by using barbells, dumbells, ect. Why? Because chances are you won't find a person that weighs 300, 400, 500, whatever to practice with on any given day. Now you might say, "But I would be fighting in my weight class (205 being mine) so why the hell would I care if I can bomb a 300 pound person?" Well the fact is, the higher the weight you practice with, the easier the lower weights are to handle. (And by lower weights I mean the people in your weight class) Even if the motion you train is not a perfect copy of picking someone up and dropping a person. The muscles used in this act are being trained to be much stronger then what you need, and with practice (grappling) you learn to use them in a sport specific ways. Beyond that, it allows you to handle people of your body weight in a much faster manor then if you don't strength train at all.
For example, I have not a lot of grappling under my belt, about 3-4 months, and one of the people I grapple with has been doing it for 2-3 years. Now we weigh about the same (200-205). I powerlift 4 times a week and he never lifts weights. He can easily drop a person in his weight class and has done so on many occasions in fights. He can somewhat manage to get a person who is 260 (Another one I train with), but that is tough for him. I on the other hand, with very little knowledge and horrible technique, have really no problem bombing people who weigh that much. With technique I guarantee you I will be able to do it faster and with less strain then him.
How does this apply to sandbags? Well if your body is used to picking up and slamming a 300 pound sandbag, it will make it that much easier to do so against a 180 pound human. And I guarantee the guy using the sandbag will be more prepaired and less strained then the guy who doesn't. I find the old excuse, "I don't lift weights because they aren't sport specific" as the battle cry of the ignorant at best.
And sorry if I totally kill what James wrote. I'm pretty sure the real version is still at his site.