lower limb unloading simulate microgravity and induce an atrophy :

http://jap.physiology.org/content/70....full.pdf+html

"The major findings of this study were the marked decreases in muscle strength and CSA observed after 4 wk of unilateral lower limb unloading. These responses are of similar magnitude to those produced by 4-5 wk of bed rest (5, 7, 10). This experimental model appears to be a valid simulation of bed rest and hence of changes (29) within the musculoskeletal system that occur in microgravity."

clic on "full text", see the picture.