Do Dynamic Fat and Fat-Free Mass Changes follow Theoretical Driven Rules in Athletes?

Area of Science:

• Sports Science
• Human Physiology
• Body Composition Analysis

Background:

• Optimizing body composition, specifically fat mass (FM) reduction and fat-free mass (FFM) preservation, is crucial for athletic performance.
• The dynamics of body weight (BW) changes and their impact on FM and FFM during athletic training seasons are not well understood.

Purpose of the Study:

• To analyze the contributions of FM and FFM to BW changes in athletes over a season.
• To determine if these contributions align with established rules and predictions for body composition changes.

Main Methods:

• Seventy athletes across various sports were monitored from the start to the competitive phase of their season.
• Body weight (BW), fat mass (FM), and fat-free mass (FFM) were assessed using a four-compartment model.
• Energy densities were calculated to determine the contribution of FM and FFM to BW fluctuations.

Main Results:

• Athletes losing BW (>1.5%) experienced significant FM reduction (90% of BW change) with minimal FFM loss.
• Athletes gaining BW (>1.5%) showed significant FFM increase (95% of BW change) with negligible FM gain.
• Observed FFM changes were inversely related to predictions from the Forbes Curve, indicating deviations from established models.

Conclusions:

• During BW loss, athletes predominantly utilized FM for energy, unlike predictions for non-athletic populations.
• During BW gain, athletes prioritized FFM accretion, with minimal FM increase.
• The composition of BW changes in athletes during training seasons does not conform to standard predictions for lean or obese individuals.