Body Composition: Assessment of Athletes

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• Can you explain Brozek fat % vs. total fat%?
  • There's a 6-compartment model comparison study and there's multiple 2-compartment models that they use. In 2-compartment models, depending on the cadaver analysis, Brozek uses a 2-compartment percent calculator based on certain densities on certain cadavers. There's a Siri-2C model that uses a different percent fat calculator to convert body density into a percent fat. That's really the difference and that could could be a whole talk looking at different 2-compartment models. But overall, different 2C models are based on different cadavers and all tend to have the same amount of error, specifically that body water assumption. Brozek is typically the most accurate for athletes. When tracking changes, don't change the model.
• What is your opinion on the digital weight scales (the ones that include their app) in terms of body composition accuracy?
  • It depends on the athlete and the individual. To track body comp changes 5-10lb weight change (constant) should happen over the course of a month. Most athletes aren't going through this. To understand the body fat error, you need to have a change in weight because you're not going to exceed the error in the device itself. For home scales, you need that weight change to be over 5-10lbs (at least 12-15lbs) before you can see what's going on at a composition level. If you're using too much information without understanding and modifying based on that, you can do more harm than good.
• Do you have a preference between Hologic and GE manufactured DXA machines when it comes to body composition assessment?
  • Since GE does so many things with their company from lightbulbs to DEXA machines vs hologic being focused on DEXA, Hologic puts more time and money towards the body composition side of their company with better support. They both have the same precision and accuracy and give good data, but Hologic has better prices and software for body composition.
• How can we access these databases that give optimal body composition for position in sports?
  • Yes, if you have anthropometric data, use the exercise science toolkit, its free. If you have DEXA data, go with FitTrace. If you don't know literature or don't know standards based on your method, you really need to find somewhere that has that. DEXA and FitTrace have that; ISAK has a massive database. Other than that you'll have to find specific publications using specific equations for your specific devices otherwise you can't compare.
• Does the time you exercise/train throughout the day effect your metabolism?
  • It all affects your metabolism! You have to pay attention to your body