Using the standardised B-mode ultrasound method, sums of subcutaneous adipose tissue (SAT) thicknesses (D) determined by experienced measurers at eight sites (on trunk, legs, and arms) can be determined with high accuracy and reliability: the 95% limit of agreement for experienced measurers (three in each of the two experienced study centres C1 and C2) was below 1.5 mm (embedded fibrous structures included: DI), and below 2.2 mm (fibrous structures excluded: DE). This enables monitoring changes of SAT mass in athletes (which forms the dominating part of total body fat) with an accuracy of about 0.2 kg. The median thickness measurement deviations at the individual eight sites were all below 0.2 mm. Measurement differences of novice measurers, after a 2-day course, were approximately three times larger.

This ultrasound method also allows to quantify the amount of fibrous structures (fasciae) embedded in the SAT: DF = DI − DE. The amount of this connective tissue was significantly lower in the 39 female elite athletes of various sports (median of 11%) when compared to the 37 male elite athletes (18%). Median SAT thickness sum DI of the eight sites was three-times higher in the elite female athletes compared to their male counterparts (51 mm vs 17 mm).

In this group of elite athletes, there was no significant correlation between SAT and body mass index (BMI). The BMI is a measure of relative body mass, but not a useful tool to determine body fat. This holds also true for the mass index MI, but this improved measure for relative body mass considers the individual's leg length, which the BMI ignores. Differences (MI-BMI) were large in several cases and ranged from − 1.7 to + 1.3 kg m−2 (median BMI was 22.6 kg m−2), which supports the suggestion to include leg length (or sitting height) in all basic data sets of athletes and patients and thereby to assess body mass with respect to body dimensions in an improved way.