Did you even TRY doing a prior search of the forums to see whether in all V3's years of existance this question hasn't been already raised and answered?
DPH

I try but don't even know what keywords to use. my keywords don't return any good results. my keywords are "V3 knee bending problem" or "v3 knee" or "v3 fix knees"

Oh come now, be immaginative!  Try knee, try bend, and DO try to expand the search beyond the default past 45 days.  I always set my searches to 'newer than 100 years'.  That way I insure to get ALL the archive files on a subject, and then USE a bit of patience and elbow grease, and start sifting through the files.  They date back to 1999, so there must be TONS of usefull information buried in them.
DPH

there is a set of morphs in the freebies. by maveris, i think. A. ps: it is ok to answer a question. it is also ok not to answer a question. but to say: 'go, find your answer' is a bit ...

OK bad image. I keep forgetting P7 is set the other way for compression. That will teach me to not export the image in a proper image format. Never use JPG.

While working for a simple fix I found that by using a magnet on the thigh it should work for most purposes. Typically a thigh will flatten or widen when the leg flexes significantly, this magnet tries to create that effect.

After creating a magnet on the right thigh it was edited to have the following settings:

Mag Base 1    0    scale    Spline    0.1537    10
Mag Base 1    0    yrot    Spline    0.0000    2
Mag Base 1    0    xrot    Spline    0.0000    1
Mag Base 1    0    zrot    Spline    0.0000    3
Mag Base 1    0    xtran    Spline    -0.0389    4
Mag Base 1    0    ytran    Spline    0.1720    5
Mag Base 1    0    ztran    Spline    0.0397    6

Mag 1    0    scale    Spline    1.0000    10
Mag 1    0    xScale    Spline    1.5920    7
Mag 1    0    yScale    Spline    1.0000    8
Mag 1    0    zScale    Spline    1.0000    9
Mag 1    0    yrot    Spline    0.0000    2
Mag 1    0    xrot    Spline    0.0000    1
Mag 1    0    zrot    Spline    0.0000    3
Mag 1    0    xtran    Spline    0.0000    4
Mag 1    0    ytran    Spline    0.0000    5
Mag 1    0    ztran    Spline    0.0520    6

Mag Zone 1    0    scale    Spline    0.0769    10
Mag Zone 1    0    xScale    Spline    0.5720    7
Mag Zone 1    0    yScale    Spline    1.0000    8
Mag Zone 1    0    zScale    Spline    0.6160    9
Mag Zone 1    0    yrot    Spline    0.0000    2
Mag Zone 1    0    xrot    Spline    0.0000    1
Mag Zone 1    0    zrot    Spline    0.0000    3
Mag Zone 1    0    xtran    Spline    -0.0389    4
Mag Zone 1    0    ytran    Spline    0.2400    5
Mag Zone 1    0    ztran    Spline    -0.0213    6

The numbers that matter are the ones after spline for each entry. So the magnet base scale is 0.1537 and so on. These values are in Poser native units. If you have Poser setup for inches multiply the translations by 103.09 or switch to Poser native units while you enter the values.

For the other thigh the magnet would have the same values except that the x translations are mirrored.

I wish I could save the magnet but Poser 6 does not save magnets properly.

Anyone is free to improve on this and repost the new settings.

good luck,

FlyerX

V3 shouldn't be THAT bad.  

Dont twist the shin in poses like this (it distorts the bend area). Use side-side on the foot instead.