Changes

These are cheap ([http://www.amazon.com/gp/product/B000G7YW74 $6]), but tricky to use accurately. Slight I have several of these calipers and each one requires different pressure to 'click' and record the skinfold. This difference in pressure can make a big difference in the skinfold measurement. Also, slight changes in location of the measurement can make a big difference to the reading, so practice is required to get the same spot each time. With lower levels of body fat, the resolution of the calipers can also be is a problem. The calipers only measure the fat under the skin, and at a few locations. There is significant person to person variation in fat distribution through the body, limiting the accuracy even with expert usage. The two big advantages of calipers are that they are cheap, and they measure the body fat directly.

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 there their accuracy is limitedquite 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.