The results showed his body fat to be
an athletic 18%! No way in h*ll – so we
referred Alan for a DXA scan to see if
that would tell a different story
The 30-second article
• Researchers compared the accuracy
of a bio-electrical impedance analyser
(BIA) to that of a DXA scan
• BIA is a less expensive option and
uses electrodes placed on the body to
measure total body water and
estimate body composition
• In DXA scans, two different energy
levels of X-ray pass through the body
and measure fat, muscle and bone
levels
• The per cent body fat estimated by the
BIA was significantly lower in males
and significantly higher in females,
compared with the data provided by
the more accurate DXA scans
• DXA involves very low doses of
radiation, the perceived ‘downside’ of
which may be offset by the potential
benefits gained from correct
assessment.
loss programs and other health related
fields to assess the risk factor of obesity.
DXA, as the gold standard, is generally
more expensive than BIA assessment and
typically not available in most health and
fitness facilities.
Pros: This is a good practical study,
between BIA and DXA: what was problematic
in the findings was that the differences seen
were gender specific. Congratulations to
the authors for then developing correction
equations to improve the accuracy of the
BIA equations. For example, the correction
equations for per cent body fat (specific to
the BIA device used in this study only) for
males was 14.098 + 0.694 x % fat (BIA) and
females was -3.263 + 1.019 x % fat (BIA).
There is no doubt the technology of the
BIAs continues to improve and it is useful
to help individuals who are attempting
to monitor their adiposity or lean mass
(muscle) levels.
30 | NETWORK WINTER 2018
It should be noted that when using DXA the subject is irradiated.
In the case of those suffering from serious health concerns due
to excess weight, suspected poor bone mineral density or other
conditions (such as use of medications that might impact bone
mineral density), then the use of DXA measurements is supported.
This is similar to getting an X-ray to check for a broken bone, the
potential benefits gained from correct assessment can greatly
outweigh any negatives from a small dose of radiation. While the
dose of radiation from DXA is about the same as the level you’d
be exposed to by taking a short flight, it still exists. With respect to
radiation, there is no threshold dose: any radiation can have some
negative effect. It therefore should be cautioned against unnecessary
or repeated DXA use when there is not an apparent health benefit.
This benefit can arguably be as simple as gaining extra motivation to
exercise, however outside of clinical conditions measurement via BIA
may be sufficient. As subjects using BIAs are not subjected to the
same radiation level as that involved in DXA, improving the accuracy
of BIA (as per the authors’ work) is to be commended.
Cons: Unfortunately, BIAs are based on predictive modelling
using sample population averages and are sensitive to the different
individual characteristics of people. Factors as diverse as hydration
levels (body fat overestimated due to dehydration, by as much as
5kg in some research), skin roughness, and whether the subject
has recently eaten or exercised can dramatically affect the results.
Although the participants in this study were asked to fast for a
minimum of 8 hours, there was no mention of avoiding strenuous
exercise prior to the testing to ensure they had a normal state of body
water content (‘euhydration’ for those of you looking to expand your
medical vocabulary!). In fact, due to reduced electrical resistance
in the body after exercise, other studies (Khaled, 1988) have shown
fat mass as being underestimated by up to 12kg when BIAs have
been used after exercise. This finding is particularly noteworthy for
those PTs using BIA in the gym, after a client’s training session.
Additionally, as females were included as participants there was
no mention of whether they were tested during their menses, which
could also dramatically affect the accuracy of the results.
If ongoing DXA scans are not a financially viable option for clients
and you want to choose the ‘next best thing’ in terms of a BIA, the
best thing that you can do is to get yourself a DXA scan, and to
then experiment with a number of BIA units to see which one’s
results come closest those you got with the DXA. Then, one hour
later (having consumed nothing, expelled nothing and not exercised)
reassess and see which unit gives the (near) exact same reading as
the first time on the BIA monitor.
In fact, I was once asked by a fitness facility I worked with to advise
them on their potential purchase of a BIA unit. I recommended that
they ask the sales rep to loan the unit to them for 4 hours so that they
could carry out the exact same process outlined in the paragraph
above with a number of club members of varying body types, from
lean to overweight. The rep became defensive at this request and
questioned the motives behind it, before refusing to loan the device.
This, I assured the facility management, was not the behaviour of
someone that was confident in the reliability of his wares. They took
my advice on board and did not purchase that particular unit.
Dr Mike Climstein, PhD FASMF FACSM FAAESS AEP is one of Australia’s
leading Accredited Exercise Physiologists. He is a faculty member inClinical
Exercise Physiology, Sport & Exercise Science at Southern Cross University (Gold
Coast). [email protected]
Joe Walsh, MSc is a sport and exercise scientist. As well as working for
Charles Darwin and Bond Universities, he is a director of Fitness Clinic in Five
Dock, Sydney. fitnessclinic.com.au