Friday, July 31, 2009
Whether you’re building or cutting, you should have a reliable method for estimating your body fat percentage. As you gain - or lose - weight your body fat percentage will tell you what the change means. There are a variety of techniques that can be used that vary in time, ex- pense, and accuracy/precision. The pros and cons of each are outlined be- low.
DEXA: “DEXA” stands for Dual Energy X-Ray Absorptiometry. As the name
implies, low level X-rays at two di erent energy levels are used to deter-
mine body composition. DEXA scans can di erentiate between soft body
tissues and bone - which makes it especially valuable for providing esti-
mates of bone mineral density.
Pros: DEXA scans are:
highly accurate. DEXA is considered to be the “gold standard” for body
non-invasive. All you need to do is lie on the table and hold still.
requires no special preparations. There is no need to fast prior to the
test, or restrict activity, medications, etc.
radiation exposure is low. The amount of radiation used for body comp
testing is equivalent to a single day’s worth of normal background ra-
Cons: DEXA scans are:
expensive. The prices vary by facility, but I’ve seen some programs that
charge around $70 - $150.
inconvenient. DEXA units are typically housed in hospital, university,
and other clinical/research settings. They aren’t freely accessible to the
public - you need to be referred by a healthcare provider, enrolled in a
research study, or participating in an outpatient hospital or clinic pro-
gram to access the service
A DEXA scan - if you can get one - is best used as an occasional check to
verify your own body comp estimates.
Hydrostatic (Underwater) Weighing: Hydrostatic weighing is another
highly accurate method for assessing body fat percentage. The test actu-
ally measures total body density. Since the density of fat is less than lean
mass (fat oats!), the contribution of fat and lean tissues to your total body
density can be determined mathematically.
Pros: hydrostatic weighing is:
accurate. Hydrostatic weighing was considered the method of choice
for body composition testing prior to the development of more high-
less expensive than DEXA. The typical cost of a test runs around $25
- $50 (US).
Cons: hydrostatic weighing is:
inconvenient. Since immersion is required, the test is limited to facili-
ties that provide a “dunk tank.” Although some larger, more expensive
private health clubs and facilities now o er this service, your best bet is
to go to a local university athletic department.
complicated. Prior preparation is required: you cannot eat or exercise
within 3 hours of the test. A swim suit and towel are also needed. Re-
sidual lung volume also needs to be measured to correct for the error
that inhaled air can introduce into the assessment.
Air Displacement Plethysmography: This is popularly known as “Bod Pod”
testing. The Bod Pod measures total body density, similarly to hydrostatic
weighing. The di erence is that the air displacement, rather than water, is
used. Bod Pod units are sold commercially, and can be found in a variety
Pros: The Bod Pod is:
fairly accurate. Clinical studies have shown that Bod Pod results are
comparable to hydrostatic weighing, although in practice, discrepan-
cies have been noted.
convenient: Bod Pod measurement is similar in accessibility and price
to hydrostatic weighing, but considerably less time consuming and
Cons: The Bod Pod is:
less accurate than hydrostatic weighing for certain populations and
Bioelectrical Impedance Analysis (BIA): BIA assessments of body compo-
sition actually measure the resistance to a low, safe electical current passed
through the body. Electricity is conducted more readily through body wa-
ter contained in muscle and other lean tissues than it does through fat.
More sophisticated, research grade BIA devices rely on hand and foot elec-
trodes, whereas home-use devices (scales and hand held instruments) rely
on foot-to-foot or hand-to-hand circuits.
Pros: BIA measurements are:
simple and fast. BIA devices are often used in commercial gyms and
clinic settings for this reason.
relatively inexpensive. Home devices cost about $50 - $200. The more
expensive home units generally o er multiple test modes, such as “ath-
Cons: BIA measurements are:
imprecise. Total body water uctuates throughout the day. The most
accurate readings are made using clinical instruments and subjects who
adhere to the pre-test protocol (no eating/drinking for several hours be-
fore the test; no exercise, ca eine, or alcohol 24 hours before the test).
Needless to state, it is very di cult to standardize testing conditions
with a device designed for frequent home use. Home measurements
often vary 3 - 4% over the course of a single day.