I'd say it's tubes of stockinette -- rapid increases after the ribbing, and rapid decreases as you get to the elbow ribbing. Not that 3-d modellers have to make things close to 'reality'.
I'd make them reversible, if possible, so that you can wear them either way. How I'd do it would be average the below-elbow and wrist measurements, and knit a ribbing that's not too tight for the elbow, but not too loose for the wrist. Do an increase in maybe every knit stitch of the ribbing, and then mirror those increases for the decreases. ie, if you've got a k2p2 rib, increase in the knits, and say, k2tog twice, k 2 for the row leading to your ribbing.
Just kinda thinking "out loud" as it were.