i rememeber laura's post and she did say she only burned 5 more calories when using two risers on each side. once i changed to one riser on each side, i noticed my knees felt better (i had used 8" for years). i think if you are really tall (i'm not) then an 8" height might be better, but for me at 5'3, one on each side is fine. i just try to jump higher and really concentrate on my moves. i have been very happy since i switched to one on each side. although, when doing weights, i pile four risers on each side. i like being high up so i can really extend my arms for things like pullovers.