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I see references to body fat %, the ranges for great to obese, but I don't know where to find information on body muscle % or how to measure it? I'm assuming it goes up as body fat % goes down if you're doing the same exercises - right?

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To my knowledge there is no formula for calculating body muscle percentage. Once you have calculated your body fat percentage, the rest is considered lean body mass, consisting of lean muscle, bones, organs and fluids.

  • If your body fat percentage decreases, then your lean body mass percentage increases. However, if you are not eating sufficient nutrients and your weight decreases but your body fat percentage does not, then you could be losing weight from lean body tissues like muscles. In the extreme you could be losing bone mass.

Two ways you can track muscle growth and definition is with girth measurements and photos:

  • Girth or Anthropometric Measurements: One way to track increases in muscles is by measuring the girth of the muscles at designated points and re-measuring over time. Of course the limitation with this method is that it simply indicates an increase (or decrease) in size, not the composition. However, if the muscle definition is improving along with an increase in girth measurement, then the increase in size is likely to be due to an increase in muscle mass.
  • Photo Journal: Another method of keeping track of progress is by keeping a photo journal. Make sure to keep the same camera set up and stand in the same place each time.

So to rephrase your question: "What is a good lean body mass percentage?" Calculate your body fat percentage and subtract that percentage from 100. For example, if you are a reasonably fit male and your body-fat percentage is 14-17%, then your lean body mass would be 86-83%. Generally speaking, however, the body-fat percentage is referenced. (See body fat % charts - on our site). And yes, as your body fat percentage decreases, your lean body mass increases proportionally.

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Your body consist of muscles, fat, bones, organs, connective tissue and cartilage. Where everything other then fat and muscles have a constant weight over time. Measuring fat will therefore be the only parameter you need to calculate your lean mass (muscle weight including bones etc). You just takes 100% - Fat% and it will answer your question.

Fat can be measured by a variety of different methods. A pretty reliable home test is just using a tape-measure and use the navy circumference method. Although not very exact, it is a pretty good way of tracking differences in body composition. It is probably more reliable when losing fat then gaining muscle though.

There are also cheap calipers for home usage. But the method is pretty unreliable if not measured by a professional. I myself use a bioelectrical impedance scale, caliper and navy circumference and then take a arithmetic mean of the three. If you want more a more reliable method you probably need to go down to the gym where they have more exact methods.

If you for some reason specifically want to know your exact muscle mass percentage not including weight of bones. Then you probably need to do DEXA (Dual Energy X-ray Absorptiometry) which I think can single out muscle mass. If you want to track progress in muscle mass, you are probably better off tape-measuring the circumference of each body part and forget about percentages.

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A slight misconception - bones vary in weight and thickness according to dietary intake and other needs. Bones are the primary storage location for calcium, and in times of need the body will release hormones that cause bones to give up calcium which reduces their weight. You also forgot to list organs, which can also vary in weight (such as the liver, which is a primary glycogen storage location). There is actually very little in the body that remains static in weight from day to day. –  JohnP Oct 17 '12 at 14:28
    
You are absolutely right. I made some shortcuts to make a simplified argument. The real answer is, if you want to know the actual muscle mass DEXA or autopsy is the only reliable ways to go. I think a decent assumption is that bone mass is relative to muscle mass and organ weight will fluctuate around a "real" value. So by doing a set of samples with some statistical analysis will give a fairly good trend or mean value. –  conMan Oct 17 '12 at 16:41
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There has many different methods to measure the fat%, such as Hydrodensitometry Weighing, Calipers (Anthropometry- Skinfold Measurements), DEXA (Dual Energy X-ray Absorptiometry), NIR (Near Infrared Interactance), Magnetic Resonance Imaging (MRI) and so on. But for different races,even a same method could get different result. So you can go to a gym, and they can help you to do a test, normally they use Calipers.
For an ideal fat%, different age and gender have different standard, for example:

male    <30(age) 14-20%    >30(age) 17-23%     >25% Obesity 
female  <30(age) 17-24%    >30(age) 20-27%     >30% Obesity 
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Mark, the question asked about Body Muscle percentage, not about Body Fat. –  Moses Oct 17 '12 at 16:50
    
oh.....i made a mistake....sorry. –  Mark0923 Oct 19 '12 at 7:58
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