Evaluation of fat-free mass hydration in athletes and non-athletes.
Level 4 - case-series / case-control
Cross-sectional comparative physiological evaluation
PubMed 32239309 · doi:10.1007/s00421-020-04356-y
What was done
The study evaluated fat-free mass (FFM) hydration in 128 healthy young adults (athletes: 61 men, 36 women; non-athletes: 19 men, 12 women) using two-component (2C), three-component (3C), and four-component (4C) body composition models. Body density was assessed using underwater weighing or air-displacement plethysmography, total body water via deuterium dilution, and bone mineral content using dual-energy X-ray absorptiometry.
What was found
There was no significant difference in 3C-model FFM hydration between athletes (men: 72.3 ± 1.3%; women: 71.8 ± 1.3%) and non-athletes (men: 72.1 ± 1.2%; women: 72.2 ± 1.0%), with an overall mean of 72.1 ± 1.3%. The estimation error for percentage fat between the 2C and 4C models correlated strongly with 4C FFM hydration (r = 0.96), bone mineral content (r = -0.70), and total body protein (r = -0.86).
Why it matters
Mean fat-free mass hydration remains close to the traditional 73% assumption and does not systematically change with athletic status. However, individual variations introduce substantial error into simplified two-component body composition assessments compared to multi-component models.
Limits
The sample was limited to young adults with an imbalanced ratio between athletes (n = 97) and non-athletes (n = 31). Two different methods were used for body density determination (underwater weighing or air-displacement plethysmography), and specific sports, training regimens, or hydration control protocols were not detailed in the abstract.
Cited by
- supports Lean muscle mass is highly hydrated tissue, whereas fat mass contains very little water.