Thanks for all the replies so far.
It's interesting that some have noted the weight differences between the DA's since the claimed weights from the manufacturers are all pretty close:
FLEX XC3401 5.73 lbs
PC7424XP 5.75
G110V2 5.5
GG6 3RD GEN 8 (shipping weight is all that's listed so this is high)
RUPES 15 5.3
RUPES 21 5.5
So it must be more about the apparent weight while using it, due to the balance of each machine. Either that or the manufacturers misstate the weights.
I know my previous post was a little rough (since it tried to address too many things) but the main message in it is still valid, which is that Strain = Work x Time (<-- this is way to simple, so please no flaming)
Here are a bunch of the elements that come to play in the biomechanical calculation (and since I am about to start my day at work I may miss a couple of things)
1) The weight of the machine
2) The vibration of the machine
3) The weight of the counterweight
4) The throw of the machine
5) The speed of the machine
6) The grasp you have on the machine (hand positions)
7) The leverage pertaining to the joint evaluated (shoulder, elbow, low back etc..)
8) The applied pressure on the machine
9) The speed of the movement produced with the machine
10) The linear and angular force vectors associated with the directions to or away from the joint being evaluated
11) The isometric, isotonic and isokinetic properties of the muscle group surrounding and protecting the joint being evaluated (ie. slow twitch and fast twitch fiber concentration)
12) Obviously you have the length of time spent in the position and composition of the muscle protecting the joint
13) You also have pre-existent injuries and instabilities which may have temporarily or permanently affected the biomechanical capacity/tolerance of the tissues at hand
etc.......
As you can see it get a lot more complicated than "what is the best machine for low back pain?"
So how can we simplify this? Well, the short of it is that you can only change the things you have control over. You can't change the weight of the machine but you can buy another. You can't change the weight of the machine but you can reduce the time spent on it. For the business minded people, it is all about the cost/benefit ratio! To improve profits you need to decrease the cost, and improve the returns. Your muscular system works exactly the same.
Do yourself a big favor and eliminate the stupid concept of "No Pain = No gain", this only serves to "rob Paul to pay Peter"..... everybody pays up in spades in the end!!!
Same as how you treat paint, you need to:
1) Prevent and minimize exposure
2) Prep
3) Work
4) Maintain
--->You should do the same on your body!!
To exercise on a regular basis serves to prep and maintain the body, but you still have to prevent and minimize exposure (this is where proper ergonomics come in).
I don't mind chatting about ways I use to reduce the stress on my own back and shoulder and neck (considering I am 6'6", 240lbs ex-basketball player (college) with prior L5-S1 disc herniation) but understand that my solutions do not apply to all; and my tolerance and capacities are not the same as all; and the list goes on.
I preach the COMMON SENSE approach to my patients every day. I can guarantee that none of your guys can say that it makes sense for someone to spend 12 hrs straight polishing on a car, or stand on concrete for 10 hrs, or deal with the environmental or chemical exposure..... but we all do it!... and we pay the piper in the short and long term!
If you want to increase your life expectancy then you need to be smart about exposure especially the strain/duration factors.
P.S. I forgot to address that the weight difference of grams x hours x repeated exposure = major strain difference in the end!
