They are talking about the BodyGem or HealthGem test... you breath into the machine for about 10 minutes, it measures your RMR (resting metabolic rate) by using your oxygen consumption levels... Your RMR is the number of calories that your body burns a day just existing. I had this test done just last week, and didn't really feel like it told me anything b/c I have been eating about 800 calories LESS than what the machine said was my RMR and still have not been able to lose weight. My advice would be to find a RMR body calculator online somewhere and see what it says... The difference in what an online thing said and the MedGem was only about 50 calories... would have saved myself $65!!! Keep in mind that if you eat 250 calories a day more than your body burns, you will gain 25 pounds in 6 months! The daily 'recommended' amount of calories is 2200 a day, but if I ate this, I would be gaining weight....
Turns out that I wasn't consuming ENOUGH calories (what in the world?!?).. I added two snacks a day (about 120 more calories / 2 rice cakes for one snack and a cup of grapes for the other) and lost 3 pounds last week! FitDay helps me track things tremedously and puts things into perspective.
Good luck!!!

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aas
Isaiah 40:31... But they that wait upon the Lord shall renew their strength:they shall mount up with wings as eagles; they shall run and not be weary; they shall walk and not faint.