April 10

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ISAK Skinfold Measurements


ISAK is an acronym for the International Society for the Advancement of Kinanthropometry. Kinanthropometry is the science that deals with measuring body compostion. ISAK is the global organisation responsible for agreeing and setting standards when it comes to measuring the human body and its composition.

An ISAK Restricted Profile will give you a lot of accurate information about your body. Skinfolds, girth measurements, height, weight and even the size of some of your bones will be measured.

This data can then determine your body type and other health appropriate health factors. Your technician may even calculate a body fat percentage for you.

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What does the ISAK restricted profile involve?

After meeting your anthropometrist, they'll generally explain what's going to happen. You may get some paperwork to read over or a consent form to complete.

17 precise measurements make up the Restricted Profile. These are mass, height (or 'stature'), 8 skinfolds, 5 girth measurements and 2 bone breadths. A full ISAK profile includes 42 individual measurements.

For most people, including sportspeople, athletes and gym-goers, the restricted profile is more than enough to obtain a wealth of data on your present body composition.

To access all the required areas, you will generally have to undress. Males will normally wear shorts only, females will wear a sports top and shorts. You'll remove socks and shoes to allow for accurate body positioning.

The first stage of your assessment is known as landmarking. 

The technician needs to identify specific points on your skeleton. These landmarks are identified by drawing pen marks (dots) on the skin. From these landmarks, the technician can then work out the locations where the skinfolds need to be taken.

Using a measuring tape, the technician will measure set distances from these landmarks to find the skinfold sites. Each skinfold measurement site is marked with a cross.

The skinfold sites that will be marked are:

  • Biceps
  • Triceps
  • Subscapular 
  • Iliac Crest
  • Supraspinale 
  • Abdominal 
  • Front Thigh
  • Medial Calf

At points, you'll have to sit or stand on a box too. This allows the technician easy access to your lower limbs.

ISAK Restricted Profile Biceps Skinfold Site marked with cross

Biceps skinfold site marked with a cross

The measurements begin

Once all the markings are in place, the measuring starts. Normally you'll stand on a set of scales and your body mass will get recorded.

A stadiometer measures your height. Generally, your technician will ensure your head is in exactly the right position before taking a reading. This ensures the 'stature' recorded is genuinely your full anatomical height. That is to say, the very tip (apex) of your skull will be the furthest point from the ground.

ISAK skinfolds

Next, we measure your skinfolds.

A fold of skin is gently lifted at each site. Skinfold calipers will measure the thickness of this fold. These are precision engineered to measure thickness accurately and consistently. You shouldn't feel much discomfort, if any. A good practitioner will take measurements quickly and efficiently.

Harpenden Skinfold Calipers

Harpenden Skinfold Calipers

Girth measurements

After all 8 skinfold sites are measured, the technician measures some girths.

Basically, these are the circumference of specific body parts. For the restricted profile, these are;

  • arm (relaxed)
  • arm (flexed & tensed)
  • waist
  • gluteal girth (hips)
  • calf

Relaxed arm is taken at the point landmarked earlier - around the mid-point of the upper arm.

For the flexed and tensed girth, we're looking for the maximum peak when you tense your biceps. Waist measurement will be the narrowest part in the area between you bottom rib and the top of your pelvis.

Measurements for gluteal girth and calf are the maximum readings.

Bone Breadths

The width of 2 bones are also measured as part of the ISAK restricted profile.

Humerus breadth is taken at the elbow and femur breadth at the knee. Small bone calipers accurately measure the breadth of these two bones.

It's important to realise that body fat percentages are only ever estimations. They're based on equations, averages and assumptions.

Rinse and repeat

Once we have all 17 measurements, we repeat the whole process.

The technician takes a second set of measurements. Multiple measurements improve both the accuracy and reliability of your results.

The second set of measures are compared to the first. Ideally, both measurements at each site will be fairly close to each other. In that case, the two measurements are averages.

However, if the second measurement varies too much from the first then a third reading would be taken. Within 10% is usually sufficient. That is to say, if the 2nd measurement is more than 10% different to the first, we take a third reading. In this case, your 'actual' measurement is the median (or middle) result of the 3.

It's important to remember that, in the case of skinfolds, readings are precise to 0.1mm.

On a lean subject whose biceps skinfold is only 4mm, a 10% range is equal to 0.4mm. Take a moment and think how small that actually is. Less than half a millimetre! It's normal to repeat at least a couple of measurements.

The restricted profile data

When all is said and done, you'll end up with a restricted profile containing 17 accurate body measurements. To give a greater snapshot of your current body composition, we calculate a few more figures.

ISAK Restricted Profile Proforma Printout

Simulated printout of an ISAK Restricted Profile proforma

The first couple of measurements are self-explanatory - weight and height.

You'll then see the 'final' skinfold measurement results, in mm, for the 8 sites. That is to say, the average or median of the 2 or 3 measurements taken earlier.

With regards to the girth measurements, we make some further calculations

Corrected arm girth tries to account for the thickness of fat measured at the triceps. The measurement given shows the 'actual' arm measurement, without the fat.

Similarly, we can 'correct' calf girth too.

In adults, bone breadth measurements won't change much with consecutive profiles. They are useful though for calculating somatotype.

What is somatotyping?

Somatotyping aims to give some quantifiable measure to identify someone's body type.

Someone can be an ectomorph, endomorph, mesomorph or indeed a combination of different types.

Ectomorphs are generally 'long and lean', endomorphs a little rounder with more fat stores and mesomorphs tend to have more muscular or 'athletic' builds.

This information can be useful in a number of ways. It can be important for sports profiling athletes.

Different sports and different positions in some team sports require different characteristics.

Coaches can uses this information to pick positions and sports most suited to an athlete's body type. Nutritionists and PTs can tailor diet plans and exercise programs to someone's own specific somatotype.

More on body types...

I've another blog article detailing different methods for training different body types.

BMI looks at the ratio between a person's height and weight. Not too useful on its own, but when combined with other factors it can provide an insight into your overall health and disease risk.

Similarly, we can calculate Waist to Hip Ratio (WHR).

Divide waist measurement by hip circumference (gluteal girth) and you'll have your WHR. The higher the value, the larger a person's waist is relative to their hips.

High WHRs increase the risk of cardiovascular disease. WHR also gives an indication of visceral fat levels.

Body Fat Percentage

Sometimes, the proforma includes body fat percentage.

At a basic level, this shows what proportion of the body is fat. For example, a 70kg athlete at 10% body fat will have 7kg of fat. Several equations can convert skinfold measurements to a body fat percentage.

As you will see from the proforma, using a different equation on the same skinfold data can give quite dramatic differences in supposed body fat levels.

It's important to realise that body fat percentages are only ever estimations.

They're based on equations, averages and assumptions.

Different equations will give different results. Therefore it's important to approach this information with a pinch of salt. When comparing subsequent readings, we must compare like for like. We need to know the formula and method used.

Tracking progress

For this reason, generally the best measurement to track changes in body composition is the last, Sum of 8 skinfolds.

Adding all 8 skinfold measurements together is useful. When tracking progress, regardless to what your weight does or how your training or diet have gone, this number shows a true reflection.

If your sum of 8 skinfolds decreases, you've lost body fat. If it goes up, you've accumulated more fat even if you weigh less.

Read more about the tools I use.

Now you know what the ISAK Restricted Profile is, find out what tools and equipment I use to produce it.

List of tools and resources I use to measure body composition and track client fat loss

So there you have it, all the ins and outs of an ISAK Restricted Profile. Have you ever had one taken? If you'd like one, the whole process generally takes less than 30 minutes.

If you live in the Perth area, get in touch and I can book you in for an assessment soon.

Happy tracking!

Paul Stokes Perth Personal Trainer Sports Nutritionist Group Fitness Instructor Massage Therapist
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Paul Stokes

About the author

Paul Stokes BSc (Hons) is a Certified Personal Trainer, Accredited Sports Nutritionist, qualified Exercise to Music Instructor, Precision Nutrition coach, Massage Therapist and teaches 8 of the Les Mills Group Exercise programs. He currently works in the Oil & Gas industry as a Wellness Coach, imparting his vast knowledge and experience to improve the quality of life of several hundred offshore workers.

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