Selfies and the scale don’t tell the entire story. Not only that, I’d be willing to bet that your mirror is lying to you. Measuring your body fat is one way to get an unbiased assessment, assuming you measure accurately.

When it comes to tracking progress, you need objective measures that allow you to see progress over the long term. Some people get too caught up in the numbers, but for the majority, they need a reliable source to hold them accountable.

And, if you’re a personal trainer, your clients want results sooner rather than later. This means hard and fast data that proves your methods work. Results equal retention and higher client satisfaction – give people what they want.

Enter the skinfold caliper…

Pinch, Pull, Progress

Skinfolds are a relatively quick and effective way to measure your body fat percentage. While they aren’t 100% reliable, they are likely the cheapest way to get a semi-accurate reading.

However, I must mention one very important caveat – to ensure accuracy and decrease the influence of personal bias, skinfolds should ideally be taken by another person.

Remember how I mentioned that you want an objective measurement? Well, if you decided to pinch your own skinfolds, your subjective perspective will come into play. Everyone wants to be leaner than they really are, so you’ll intuitively pinch harder and give yourself the benefit of the doubt when it comes to the last millimeter or two.

Call in a favor from your college roommate. Blackmail your gym partner. Heck, call your mom for all I care, but don’t fool yourself into thinking that you’re above personal bias.

Better yet, pay a trained professional to take the skinfolds because they’ll understand how to assess your results and help you reach your goals.

Drink Fluid

12 Factors That Affect Body Fat Percentage Skinfold Readings

Before we get into the nitty-gritty of site selection and test execution, we need to touch on a few factors that can affect skinfold readings.

1. Hydration

Training, alcohol, carbohydrates, rehydration (post-training), electrolyte status, supplementation, and meal timing all alter fluid shifts within body tissues. As such, you want to make sure that all these factors are constant during each testing session. For example, don’t take your initial measurements in the morning on an empty stomach one day and then take progress measurements 2 months later after an arm session with 3 meals in your system. That’s not consistent, and your results won’t be reliable.

2. Training

Any repetitive physical motion shifts interstitial fluid and blood flow. As I touch on in another article,

When someone is ‘chasing the pump,’ they generate metabolic byproducts from various energy systems and also change intracellular water concentration through cell swelling.”

While it sounds helpful, this cellular swelling can lead to a temporary feeling of “fullness” within the muscle belly itself and lead to false positives (in terms of muscle growth) or false negatives (in terms of fat loss or a lack thereof).

Bottom line: All body fat readings should be taken before training, not after.

3. Alcohol

Want to know the fastest way to get leaner (at least for a bit)? Take a couple of shots. We know that excessive alcohol ingestion can promote increased urine production (diuresis) “at the expense of all cellular components,” and thus dehydration ensues.

In essence, alcohol prevents the release of ADH (antidiuretic hormone), which tells your kidneys to reabsorb water to prevent dehydration. With less ADH, you reabsorb less water, and there is the potential for thinner skinfolds and the appearance of less adipose tissue. So to promote reliability, it’s best to avoid alcohol consumption for roughly 3 days before testing.

4. Carbohydrates

For every gram of carbohydrate that is converted and stored as muscle glycogen, you will also store roughly 3-4 grams of water.

Think about the name for a second – carboHYDRATE. Makes sense, right?

But if you choose to have a massive refeed or an excessively high-carb day (typically followed by lots of water) to augment training volume, you might throw off skinfold measurements due to changes in interstitial water concentrations.

5. Sweat Loss and Rehydration

As I touched on in point #1, fluid shifts will occur with training. Not only that, recommendations are typically made for individuals to hydrate before, during, and after training. The usual recommendation is to drink 20-24 ounces of fluids for every pound lost during exercise. However, consider the fact that this will drastically skew scale weight, girth measurements, and perhaps even skinfold measurements, depending on the training type, carbohydrate intake, and electrolyte status.

6. Electrolyte Status

To further explain my previous point – water alone won’t promote proper rehydration. Water follows electrolytes, so if your electrolyte status is low, then water alone won’t get the job done. Want to drive more water into each cell? Work to replenish electrolytes after training – namely sodium, calcium, chloride, magnesium, and potassium. To quote Dan Garner from Alan Aragon’s 2016 Research Review:

Exercise and repeated muscular contractions can reduce body pH. The acid-base balancing effect of electrolytes can help return the body to homeostasis quicker, but if electrolyte status stays low you will continue to feel weak in your next workout. Electrolytes are so important towards hydration that in the absence of electrolytes no significant differences in hydration were seen between beverages containing and omitting CHO.”  Dan Garner “Bridging The Gap Between Hydration, Electrolytes, and Athletic Performance”

As I touched on in most of my prior points, fluid shifts change caliper readings as well as scale weight. Therefore, it’s wise not to manipulate electrolytes aggressively around skinfold tests. In other words, don’t cut water or sodium before a test in the hopes that your results will drastically improve.

In the end, you simply generate false hope by temporarily altering hydration. However, once you return water and sodium to the original levels, fluids will shift, and your “dramatic improvements” will quickly disappear.

7. Contractility

If you drive up glycogen stores, which draws in additional water, and then try to take body fat measurements of a fully contracted muscle, you will register a false positive, meaning the muscle will briefly appear fuller.

That’s not to say the gains aren’t happening, but it will be very difficult to replicate the same conditions of a contracted muscle in the next trial. If you ate 3,500mg of sodium in your last test, are you sure you ate 3,500mg this time? Better yet, did you have all 3,500mg before testing last time, or did you only have 2,000mg before and 1,500mg after?

See the problem? Don’t flex for measurements unless you’re just looking to inflate your ego.

8. Supplementation (Creatine)

Besides causing a slight bump in the number seen on the scale, creatine can also increase intracellular water retention. You see, creatine works to replenish a molecule known as ATP (aka cellular energy), but it can also lead to slight water weight accumulation.

Don’t despair, though. Reread point #1 if you need a refresher! This water weight can actually enhance hypertrophy in the long run. But this can also be a compounding factor for skinfolds because you want to make sure all conditions match between trials. In other words, don’t start taking creatine between skinfold trials. Either use it through all the tests or don’t use it at all. Regardless of what you choose, don’t manipulate too many variables, or you’ll mess with the data and won’t be able to see any reliable markers of progress.

9. Meal Timing

When you consume a meal, you up-regulate enzymatic factors for digestion, trigger muscle protein synthesis (MPS), replete muscle glycogen, stimulate fat tissue creation (lipogenesis), and a variety of other functions.

However, you must keep in mind that the size, frequency, and timing of meals before skinfold testing all play a role in individual trials. If you have a massive meal just before testing, this will yield different results than a fasting trial upon waking.

Also, consider the difference in taking body fat measurements after a full day of eating, which can push upwards of 4,000+ calories for some individuals, versus measurements before the first meal.

10. Texture and Location

For the sake of reliability, take all measurements on the same side of the body. It is normally assumed that fat depositions are fairly symmetrical, but sometimes, strange things happen. So, remain consistent with either the right or left side.

On top of that, make sure that you’re not wearing any lotion or moisturizing cream, and that includes earlier in the day before testing. This can skew the results and lead to a false positive if the caliper slides.

All body fat measurements should be at the largest circumferential point. In other words, take it around the base of the muscle. If you like to measure a little higher up, then go for it, but make a note of it (either mentally or physically) to ensure that all trials are equal.

11. Time of Day

Diet and exercise are both fantastic tools, but at the end of the day, what are you really trying to manipulate? Hormones and physiology. Your lifestyle, nutrition, and supplementation all influence your hormones, which in turn dictates physiological adaptations.

Hormones can also fluctuate based upon the time of day, which is known as diurnal variations. Some argue that this is likely one of the smaller areas of influence when it comes to skinfold measurements. However, we must be careful not to dismiss the physiological impact of hormones.

12. Human Bias

You can’t avoid this on your own, no one can. As such, recruit the help of a friend or trusted cohort (think: gym buddy) to help you stay honest.

Everyone wants to continually make progress, so we subconsciously pull the tape slightly tighter or looser, depending on your goals. When you factor in the human psyche and a continuous desire for improvement that seems to permeate much of the fitness industry, you quickly find that reliability flies out the window.

Measuring Your Body Fat Percentage

If You Remember Nothing Else, Remember This…

All these factors play a role, regardless of how large or small the impact, the most important thing you must keep in mind is BE CONSISTENT.

If you decide to have two meals and a half-gallon of water before testing, you need to have a half-gallon of water and two meals in your system the next time you test. If you’re confused by all the confounding variables and can’t seem to decide the best time/conditions to test under, simply test first thing in the morning upon waking when you have nothing in your system (food or water).

Give yourself the best chance for a consistent reading by following this checklist before your next skinfold measurement:

  • Always test before training.
    • If possible, test at least 36-48 hours after training to allow the inflammation to subside and glycogen levels to replete.
  • No alcohol for at least 3 days prior.
  • Keep carbohydrate intake consistent for at least 7-10 days prior.
  • No major water and/or electrolyte manipulations for at least 24-48 hours prior.
  • Take subsequent tests at the same time of day as the first test.
  • Ensure similar feeding times and number of meals before testing.
  • Maintain a normal skin texture (no creams, oils, etc.) and ensure the muscles are relaxed.
  • Mark skinfold sites to ensure reliability with each subsequent reading.
  • Don’t start using creatine between different tests – either start using it before your first measurement or don’t use it during any of the following tests.
  • Take all measurements on the right side of the body for consistency.
  • Use multiple measurements at each site and ensure the same individual conducts all the tests to ensure reliability between trials.

While skinfolds may seem complex, this guide should distill the topic, while providing accurate and repeatable results for yourself and your clients. Now that you understand this, let’s discuss the actual body fat measurements in Part 2 of this series.

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