▁of ▁single ▁frequency ▁B IA ▁analyz ers ▁then ▁became ▁commer cially ▁available , ▁such ▁as ▁R J L ▁Systems ▁and ▁its ▁first ▁commercial ized ▁imped ance ▁meter . ▁ ▁In ▁the ▁ 1 9 8 0 , ▁L uk ask i , ▁Seg al , ▁and ▁other ▁research ers ▁discovered ▁that ▁the ▁use ▁of ▁a ▁single ▁frequency ▁( 5 0   k Hz ) ▁in ▁B IA ▁assumed ▁the ▁human ▁body ▁to ▁be ▁a ▁single ▁cyl inder , ▁which ▁created ▁many ▁technical ▁limitations ▁in ▁B IA . ▁The ▁use ▁of ▁a ▁single ▁frequency ▁was ▁in ac cur ate ▁for ▁populations ▁that ▁did ▁not ▁have ▁the ▁standard ▁body ▁type . ▁To ▁improve ▁the ▁accuracy ▁of ▁B IA , ▁research ers ▁created ▁empir ical ▁equations ▁using ▁empir ical ▁data ▁( gender , ▁age , ▁eth nic ity ) ▁to ▁predict ▁a ▁user ' s ▁body ▁composition . ▁ ▁In ▁ 1 9 8 6 , ▁L uk ask i ▁published ▁empir ical ▁equations ▁using ▁the ▁imped ance ▁index , ▁body ▁weight , ▁and ▁react ance . ▁ ▁In ▁ 1 9 8 6 , ▁K ush ner ▁and ▁Sch ol ler ▁published ▁empir ical ▁equations ▁using ▁the ▁imped ance ▁index , ▁body ▁weight , ▁and ▁gender . ▁ ▁However , ▁empir ical ▁equations ▁were ▁only ▁useful ▁in ▁predict ing ▁the ▁average ▁population ' s ▁body ▁composition ▁and ▁was ▁in ac cur ate ▁for ▁medical ▁purposes ▁for ▁populations ▁with ▁dise ases . ▁In ▁ 1 9 9 2 , ▁K ush ner ▁proposed ▁the ▁use ▁of