FFM measurements were compared with corresponding data using Dual X-ray absorptiometry (DXA). 
Dual X-ray absorptiometry
Accuracy of plantar electrodes compared with hand and foot electrodes in fat-free-mass measurement.This paper investigates the measurement of fat-free mass (FFM) by bioimpedance using foot-to-foot impedancemeters (FFI) with plantar electrodes measuring the foot-to-foot resistance R34 and hand-to-foot medical impedancemeters. 
bioimpedance using foot-to-foot impedancemeters (FFI)
Accuracy of plantar electrodes compared with hand and foot electrodes in fat-free-mass measurement.This paper investigates the measurement of fat-free mass (FFM) by bioimpedance using foot-to-foot impedancemeters (FFI) with plantar electrodes measuring the foot-to-foot resistance R34 and hand-to-foot medical impedancemeters. 
hand-to-foot medical impedancemeters