Tracking changes in body composition in athletes: are rapid four-compartment models valid?

Area of Science:

• Sports Science
• Body Composition Analysis
• Human Physiology

Background:

• Rapid four-compartment (4C) models are validated cross-sectionally for body composition but lack longitudinal validation in athletes.
• Assessing longitudinal changes in fat mass (FM) is crucial for athletes' performance and health.

Purpose of the Study:

• To evaluate the longitudinal validity of rapid 4C models using DXA-derived body volume (BV) and BIS-derived total body water (TBW) in athletes.
• To compare the accuracy of these rapid models against a criterion 4C method for tracking FM changes over time.

Main Methods:

• A criterion 4C model utilized DXA (bone mineral content), air displacement plethysmography (BV), and deuterium dilution (TBW).
• Rapid 4C models employed DXA-derived BV and BIS-derived TBW.
• Longitudinal changes in FM (kg and %) were analyzed in athletes with >1% change (n=60) and those exceeding least significant change (n=25).

Main Results:

• All rapid 4C models underestimated FM changes compared to the criterion 4C method.
• 4C TBW_BIS showed the smallest mean difference (0.41 kg), while DXA showed the largest (0.94 kg).
• Bland-Altman analyses revealed wide limits of agreement (LOA) for all methods, indicating variability at the individual level.

Conclusions:

• Rapid 4C models offer precision comparable or superior to DXA alone, with advantages in time efficiency and accessibility.
• While group-level tracking of body composition changes is acceptable, caution is advised for individual-level interpretation due to wide LOA.