Here is the info you need to make a deformation animation.
Go to this page:
https://jira.secondlife.com/browse/VWR-2242
And download the zipped .bvh files. Open them as a TEXT DOCUMENT and have a look - especially at the difference between TinyDeformForearmr and UnDeformForearmr. ("forearmr" means "right forearm"

Please correct me if Im wrong, but heres what I know:
The things to change are at the TOP and BOTTOM of the text file. The middle stuff should not be changed.
At the top it says
>> HIERARCHY
>> ROOT rForeArm
>> {
>> OFFSET 0.000000 0.000000 0.000000 etc etc etc
>> CHANNELS 6 Xposition Ypos etc etc etc
You need to change the ROOT to whichever body joint you want to affect.
ROOT rForearm will move the right elbow joint. It actually stretches the length of the upper arm. ROOT rHand will move the wrist join and will lengthen the forearm. Try to keep this in mind not to get confused!! ;p You can't stretch the hand itself because there is no joint at the tips of the fingers - obviously.
Another way to keep it straight is to think of ROOT forearm as you grabbing the forearm with both hands and pulling it away from the body. the forearm wont stretch because your holding it, but the upper arm will stretch like rubber.
So - STEP 1: Change ROOT to the joint you want to move.
(eg ROOT rForeArm, ROOT Head, ROOT Chest) be careful of capital letters.
STEP 2:
At the bottom, youll see this:
>> }
>> MOTION
>> Frames: 2
>> Frame Time: 0.033333
>> 0.000000 43.528519 0.000000 0.000000 0.000000 0.000000 0.000000
>> -0.075000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000
>> 0
>> 0
>> 0
Now its the 2nd row of numbers you should look at.
-0.075000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000
The first 3 numbers are the x, y, z coordinates as far as I can tell.
So, the position of joint in space relative to parent joint is:
x -0.075000 (length/shorten)
y 0.000000 (to the side of AV)
z 0.000000 (forward of back of AV)
I THINK that if you decrease the x value, (make it a more negative number) the right limb will stretch. This is for the RIGHT arm and RIGHT leg only.
For the LEFT arm and leg, and you can see in the bvh files, IN-creasing the x value (more positive) will stretch the arm.
Always compare it to the UnDeform file. The unDeform files have the "normal" values for an avatar.
NORMAL values for Av:
Right side : neg value (eg -10.2 for right forearm)
Left side : pos value (eg 10.2 for right forearm)
Try to keep these straight in your head as well

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
X Side note: For some reason, the left forearm has 3 lines of numbers X
X I assume the 3rd line is the one to change, since it has an X
X x value of 10.12 X
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Now, for the right arm, making it more negative than the "Normal value" will stretch it.
Since the Normal Value is -10.266 , lets change that to -60.00.
Save the file as a Deform_Right_Forearm.bvh file (not a .txt)
And go into SL.
Upload animation Deform_Right_Forearm.bvh
Find it in inventory
Play animation.
Viola - your right upper arm should be longer. about 5 times longer I think.
Stop Animation.
Your arm will still be long. There are 2 ways to Normalize it.
1 - Upload UnDeformrForearm.bvh and play it.
2 - Relog.
I have a touch start script (with llRequestPermissions of course)
which plays each animation in turn automatically. I have my deforem button, and undeform button and it works very nicely.
One hint:
To save 10Lndens on uploading 100 of test animations, when you login to SL, press CTRL SHFT G. (or is it CTRL ALT G??) to get a pulldown menu of Grids. Then choose the 2nd grid Aditi where you can beta test all your animations for free. When you find the one perfect animation, you can log into SL proper (Grid named Agni) and upload for 10 lindens.