• What is assessed?
• How is the measurement conducted?
• When is this method used?
• How are estimates of body composition derived?
• Strengths and limitations
• Populations
• Further considerations
• Resources required
• Instrument library
• References

Total body electrical conductivity (TOBEC) analysis is a bioelectrical technique that uses measures total body electrical conductivity to estimate lean body mass. Other dimensions can also be assessed. The method was originally developed to quantify lean tissue in meat.

The TOBEC method is based on the principle that organisms placed in an electro-magnetic field perturb the field. The degree of perturbation is dependent on the amount and volume of distribution of electrolytes present. Fat free mass (FFM) has a much higher water and electrolyte content than fat mass (FM) and the strength of the field depends on the electrolytes found in the person's body water.

1. The TOBEC instrument is a scanning device in which the participant moves on a motor-driven sled through a 2.5-MHz coil electromagnetic field at a constant rate.
2. The participant passing through the electromagnetic field of the coil absorbs heat energy, thereby perturbing the electrical field of the coil. The loss of energy detected in the coil is an index of the conductive mass of the body.
3. For adults, the whole body is scanned, and information is collected at 64 positions along the length of the body. The length of an infant's body is sufficiently short that a static measurement can be made; that is, if the outer coils are about twice the length of the body, then the infant can be placed at the center of the coils for the measurement.
4. Each assessment takes approximately 40 seconds.
5. The electrical conductivity of the participant is summarised by the an output referred to as the TOBEC number'.

Participant instructions

1. Participants should remove shoes, jewelry, and clothing containing metals
2. Participant should be fasted
3. Participant bladder should be empty
4. Participant should not be under or over hydrated
5. Clothing should be dry

This method is most accurate when measuring lean mass. However, it is not widely available and expensive to purchase.

TOBEC has been used mainly to monitor changes in body composition in women during pregnancy or lactation, in infants and in childhood obesity.

1. The human body is approximated by a cylinder of volume (V) and length (L)
2. It is assumed that V is directly proportional to: (E×L)^1/2, where E is a variable called the “TOBEC number” provided by the instrument
3. The conduction volume is assumed to be the body's total electrolyte volume
4. Thus the TOBEC instrument has been calibrated with a measurement of TBW

An overview of the characteristics of TOBEC is outlined in Table 1.

Strengths

1. Compares favorably against underwater weighing, and deuterium dilution, particularly for fat free mass
2. It is easy to use and requires no preparation from the participant

Limitations

1. It can be affected by hydration status
2. Has a high cost
3. Not widely available
4. It is based on regression equations for the estimation of TBW, FFM and FM

Table 1 Characteristics of TOBEC.

Considerations relating to the use of TOBEC in specific populations are described in Table 2.

Table 2 Use of TOBEC in different populations.

*TOBEC has been used mainly to monitor changes in body composition in women during pregnancy or lactation, in infants and in childhood obesity.

Refer to section: practical considerations for objective anthropometry

1. TOBEC scanning equipment
2. Sufficient space to house the TOBEC scanner
3. Trained operator

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