[[File:Skinfold-4.jpg|none|thumb|250px|Accu-measure calipers in action]]
==Body Fat Scales==
These Bioelectrical Impedance Analysis (BIA) scales use an imperceptible electrical signal to calculate the amount of water in the body. From this Total Body Water (TBW), it is possible to estimate body fat. This makes these scales quick and easy to use, but their accuracy is quite poor. The level of hydration has a significant impact on the reading, so readings need to be taken at the same time of day with the same level of hydration. The [[Book Review - The 4 Hour Body|4 Hour Body]] recommend drinking 1.5 liters (3 pints) of water, waiting 30 minutes, urinating and then taking a measurement. The biggest problem for an athlete is that BIA is particularly inaccurate when fat free mass, including glycogen, changes<ref name="BIA1"/><ref name="BIA2"/>. I've noticed that the day after a long run, the scales claim a much larger loss of body fat than is reasonable. I categorize these scales into three types. ===Lower Body Only===Most body fat scales have electrodes only on the feet, so the electric current only goes from one foot to the other. This only measures the lower part of the body, not the whole body. I have the Tanita BF680 which retails for 'Main article: [http://www.amazon.com/Tanita-BF680-Scale-Monitor-Athletic/dp/B000094ZGH $60]. http://ecx.images-amazon.com/images/I/41CNM5C5HSL._SS400_.jpg ===Full Body BIA Scales===These scales also use BIA, but have electrodes on the hands as well as the feet, giving a measure across the whole body. In my experience, these scales show changes in body fat far better than the BIA scales that read from the feet only. I have the Omron HBF-510 which retail for [http://www.amazon.com/Omron-HBF-510W-Composition-Monitor-Scale/dp/B001IV61J4 $60]. http://ecx.images-amazon.com/images/I/41yvY8JWRdL._SS500_.jpg ===Segmental Body Fat Scales===The latest Tanita scales use two frequencies of electrical signal and use electrodes for the hands and feet. I have not tried these scales as they are expensive ([http://www.thecompetitiveedge.com/shop/item/123-productId.184549503_123-catId.176160808.html $300]). If these scales could transfer the measurements to a PC via bluetooth, I]''d be tempted to get one. http://www.tanita.com/data/Image/products/ImageResize/Ironman---BC-558_l.jpg ===Comparison of Lower Body and Full Body Scales===Over the years I have found lower body scales show that weight loss is disproportionately from non-fat when other measures show fat levels stayed constant or dropped. Here is a recent comparison of weight loss indications from the Tanita and Omron. As you can see, the Omron shows a higher level of fat loss than the Tanita, and I believe that the Omron is more accurate. Notice the large day to day variations; this is why I measure every day and look at the overall average. I use a moving seven day average (the dotted lines) to evaluate the overall progress. http://fellrnr.com/fellrnr/BFA.JPG
These scales use an imperceptible electrical signal to estimate body fat. This makes these scales quick and easy to use, and the accuracy of the scales that measure from the hands and feet is quite reasonable. I recommend the Omron HBF-510, which retails for about $60-$65 on Amazon.com
[[File:Omron HBF-510.jpg|none|thumb|200px|The most cost effective body fat scale, the Omron HBF-510.]]
==BOD POD==
This is a chamber that works out your body volume accurately. Given the volume and weight you have the density, from which you can estimate body composition. This is the same principle used in underwater weighing, but far less unpleasant. The test costs about $25 at a gym, which makes it expensive to use regularly. There are two types of BOD POD, a recreational and a research model; The recreational model is used by many gyms and estimates lung function, whereas the research model actually measures lung volume. I found the BOD POD quick and easy, but the combination of the cost and the trip to a gym makes it tricky to use on a frequent basis. See http://www.bodpod.com/ for more details.
===Abdominal Muscle Definition===
If your body fat is low enough, the definition in your abdominal muscles (six pack) can be used to monitor body fat changes. There is no specific body fat percentage for having a six-pack, but the common thought is that you need to be 12-8% for men and 18-14 for women.
==References==
<references>
<ref name="BIA1">Body composition changes assessed by bioelectrical impedance measurements http://www.ncbi.nlm.nih.gov/pubmed/2923071</ref>
<ref name="BIA2">Changes in fat-free mass during weight loss measured by bioelectrical impedance and by densitometry http://www.ncbi.nlm.nih.gov/pubmed/2912008</ref>
</references>