磅重量時的心理矛盾

找了一些資料,原來是一種叫生物電阻分析法(BIA)的方法

http://www.slimming-methods.org/txtsrvwn.html
ANTHROPOMETRY, or
BODY  COMPOSITION  ASSESSMENT  METHODS.

Scientists and medical specialists for various reasons are interested in the percentages of types of soft tissue, adipose tissue, bone tissue, water, etc. in the composition of the body. A wide range of Body Composition Assessment Methods has been developed for these purposes. Among those are Electromagnetic Scanning (EMSCAN), the application of Ultrasound, the measurement of the natural gamma radiation of potassium (⁴⁰K, Kalium) and others. Please consult the Overview in  ³⁰ ).
For the day to day medical practice a simpler, efficient method for fat% prediction is needed. The skin fold measurement with calipers is frequently used but experience is needed to interpret skin folds at different locations and to base a prediction for the fat%  in the body on the caliper readings.
Recently the Fat Impedance Method has become popular as an efficient tool in the medical practice.
 
The BIOELECTRIC  IMPEDANCE  ANALYSIS
for FAT%  PREDICTION.

Bioelectric Impedance Analysis, BIA is not a Fat Measurement Method in the strict sense. It is a fat% estimate based on an impedance measurement. The distinction is important because both parts cause different errors.
The impedance measurement (electrical resistance is a simple form of impedance; impedance includes the effects of non-conductive  areas like the cell lining, causing capacitive effects) measures a phase shift in an applied alternating current; its frequency can be some 50 kHz. The phase shift is caused by capacitive effects in body tissues. The amount of phase shift depends on the ratio of the fatfree mass (FFM containing body fluids with electrolytes) and the fat_containing_tissue. Fat containing tissue has a low conductivity, it does not contain water.
In this type of impedance measurement two causes of errors may occur.

• The first is the great difference in skin resistance per person and even with one person in time. This can be overcome by applying the tetrapolar technique, a 4-pole measurement technique that enables the chip in the equipment to eliminate skin resistance from the measured impedance.
  
• The second cause is the sequence of various body compositions from one hand through the arm, shoulder, trunk etc to the other hand, or from foot to hand or from foot to foot. The impedance measured is connected with a mix of compositions that is not necessarily equal to the composition of each region. Research is going on in so called "Regional Impedance Measurements".
  

BIA是利用脂肪和肌肉的水份含量差別,以電阻來推測體脂比例.脂肪的電阻高,水份少;肌肉電阻低,水份多.由電阻求出身體水份含量,就可計算非脂肪體重;再由重量減非脂肪體重;求出脂肪比例.