answers the all-important question ‘are the
diet and exercise programs I’m prescribing
helping my clients reach their goals as
efficiently as possible?’
There are a multitude of ways you can
fool the body into shedding fat and building
muscle, but some of them can result in the
loss of valuable muscle.
For example, I performed a DEXA scan
on a client where, upon comparing his recent
scan to his previous one, he was shocked
to learn that he’d lost four kilograms of
muscle mass with no appreciable reduction
in fat mass. I discovered that he was
doing CrossFit six days per week, eating
excessively high levels of protein, and
consuming too few calories for his size. In
this case, he was both over-training and
under-eating – which was starkly evident
when comparing scans.
3. Estimate basal metabolic rate
There are a number of ways to estimate a
client’s basal metabolic rate. Since DEXA
provides you with an estimate of overall lean
muscle mass, you can use formulas that
include this parameter.
The
Katch-McArdle
formula
and
Cunningham formula both give similar
estimates. For example, if you have a male
client who is 100 kilograms in total body
weight, comprising 80 kilograms of muscle
and 20 kilograms of fat, his metabolic rate
would be estimated as follows (according to
the Katch-McArdle formula):
arms and legs. This gives an indication of
how well the person can use their arms and
legs to move their body weight. It answers
the questions, ‘if grandma falls, can she use
her arms to pull herself back to the standing
position?’ and ‘can she stand from the
sitting position without assistance?’
6. Monitor osteopenia and osteoporosis
A DEXA scan can provide information on
bone mineral density. Bone thinning is a
concern in older adults and can deteriorate
into osteoporosis. This condition contributes
to falls when the neck of the femur collapses
under the weight of the upper body.
Resistance training and a healthy diet
containing adequate calcium and vitamin
D work together to help strengthen bones,
or at least minimise the decline in bone
mineral density.
DEXA – the picture
of health
In the image on the left we can see a
very lean and muscular man with a very
low percentage of body fat (around 8 per
cent). In the image on the right we can see
a woman with very low muscle mass and a
very high body fat percentage. The woman
will have a more difficult time losing fat
because she has less metabolically active
muscle tissue.
(BMR) (calories/day):
370 + (21.6 x lean body mass)
370 + (21.6 x 80) = 2098 calories per day
4. Monitor visceral fat and health risk
Visceral fat is the deep belly fat that wraps
itself around the organs and secretes
substances into the bloodstream called
adipocytokines, which are known to
increase the risk of developing diabetes,
hypertension,
high
cholesterol
and
triglycerides, as well as heart problems.
DEXA provides an indication of how much
fat you have around the trunk, as well as a
ratio of upper-to-lower body fat percentage.
Taken in conjunction with other biomarkers,
lifestyle factors, and family history, this will
provide you with a more complete picture of
your clients’ relative health risk.
5. Monitor sarcopenia in your older
clients
Muscle loss in older adults can contribute
to a decline in their functional capacity, i.e.
their ability to perform routine activities of
daily living. DEXA provides information not
just on whole body muscle mass, but also
how much muscle tissue is present on the
The 30-second article
• A DEXA scan provides the most
accurate data on body composition
• By allowing you to gauge muscle, fat
and bone status, you can track
clients’ training progress
• DEXA is quicker, and more accurate
and practical than other body
composition techniques
• Scans are generally affordable,
safe and suitable for a wide range
of individuals.
and five minutes depending on the DEXA
machine used.
DEXA vs other body composition
methods
As an exercise physiologist, I have had
the opportunity to administer most body
composition tests, including hyd rostatic
weighing, skinfolds, bioimpedance analysis
(BIA), and DEXA.
Hydrostatic
weighing
can
be
cumbersome,
time-consuming,
and
impractical for most people with a busy
schedule.
The skinfold method is a quick field
measure for estimating overall body fat
from subcutaneous fat (the fat just below
the skin), but it does not give an indication
of potentially dangerous visceral fat.
Moreover, this method is highly susceptible
to measurement errors.
Bioimpedance
analysis
measures
total body water and then estimates body
composition, so the test results can be
affected by an individual’s hydration status.
Of all these, DEXA is one of the quickest
and most practical methods of body
composition, and provides you with the most
comprehensive assessment of muscle, fat,
and bone status.
Who should use a DEXA scan?
How long does a scan take?
A DEXA scan is a quick and painless
procedure. You simply lie down on the
scanning table, and a technician will position
your body to ensure you’re within the scan
zone and remain still for the duration of
the scan, which is usually between three
In my experience, the three largest
demographics making use of DEXA scans are
active gym-going people, athletes training for
an event (i.e. triathlon), and those with a focus
on general wellness looking to get a gauge on
their visceral fat and bone health.
Are there any health risks
associated with a DEXA scan?
A DEXA scan emits very low-dose x-ray
beams, even less than a chest x-ray. It poses
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