How body composition techniques measure up for reliability across the age-span.

Area of Science:

• Human physiology
• Biomedical engineering
• Exercise science

Background:

• Accurate body composition measurement is vital for intervention outcome reporting.
• Between-day precision error of common techniques and reference models remains largely unknown in population samples.

Purpose of the Study:

• To quantify the technical and biological precision error of various body composition techniques.
• To compare these errors against the reference four-compartment (4C) model.

Main Methods:

• Ninety adults (18-85 years) underwent two consecutive-day body composition assessments.
• Testing adhered to best-practice guidelines, including standardized presentation and timing.
• Technical precision was assessed via repeat measurements on day 1; biological precision was assessed between days.

Main Results:

• Most techniques demonstrated low technical and biological error (<2% fat-free mass, <3% fat mass).
• All techniques met precision cut points for fat-free mass (FFM) technical precision.
• For fat mass (FM) technical precision, air displacement plethysmography showed higher error (CV=2.13%) than other methods.
• For biological precision, only three-compartment (3C) and 4C models met FFM cut points, and DXA met FM cut points.

Conclusions:

• The choice of body composition technique depends on the study's primary outcome (e.g., 3C/4C for FFM, DXA for FM).
• However, all assessed techniques can be reliably used for longitudinal assessments in healthy adults if strict protocols are maintained.
• Low error rates were observed across a broad age range when best-practice guidelines were implemented.