Body composition in athletes:
differences between two- and four-component models

It is important to have correct measurements of the athlete*s body composition,
otherwise the advices based on these measurements are not as effective as they
should be. Body composition is measured using so-called multicomponent models.
It can be questioned whether the assumptions underlying the two-component model
are valid for (elite) athletes. However the two-component model involves less
measurements and has the advantage of being easier to perform and is quicker,
cheaper and less invasive than the four-component model - which is considered
the golden standard. Therefore, the current study will investigate whether the
two-component model is a valid method and gives reliable measurements of body
composition in two distinct groups of athletes: soccer players and swimmers.

The primary objective of this study is to investigate whether the assumptions
which are used in a two-component model hold for athletes, in other words, is
the two-component model a valid method and gives it reliable measurements of
body composition compared to the four-component model model in two groups of
athletes: soccer players and swimmers.
The secondary objective is to investigate whether measurements of total body
water (TBW) by bioelectrical impedance analysis (BIA) as measured by the Xitron
4200 hydra bio-impedance analyzer gives valid results compared to the reference
method deuterium dilution.

This is a cross-sectional study.

In this cross-sectional study, all study parameters will be measured in one
morning (~4 hours). Measurements will be performed in the fasted state, and
subjects are asked to adhere to a few guidelines concerning dietary intake and
physical activity the day preceding the measurements. To access eligibility
subjects have to fill out a short questionnaire with a few questions about
there medical history and exercise habits.
Measurements include 3 blood samples (10mL each) and 3 urine samples over a 4
hour time period. Blood sampling can give mild discomfort an can result in a
local hematoma. Furthermore, subjects are asked to drink 30g of deuterated
water - a stable isotope, which is not associated with any additional risk -
and to underwent a scan (DEXA), which uses a very low amount of radiation (<
1µSv). Finally, the bio-electrical impedance analysis to assess total body
water uses a very low current, which is in most cases unperceivable and not
harmful when meeting the in- and exclusion criteria for this study.
There is no direct benefit for the subjects, apart from receiving there
individual test results, which will give some insight in their body
composition.