“What’s measured improves.”
Peter F. Drucker
In the business world, if you fail to install a system of measurements, progress stalls. You need to have a “scorecard” in place to track whether the procedures and tactics you’re utilizing improve the bottom line: profits. And everything you implement either adds or subtracts from your profitability.
In the strength and conditioning field, having metrics as a means for keeping “score,” allows you to objectively quantify whether your training, nutrition and supplement protocols are appropriate for a specific client. So what are the best metrics for a strength coach? A training log and a pair of skinfold calipers.
Training log
A training log is anything you utilize to keep a permanent record of your client’s progress in the weight room. At a minimum, recording weights lifted and the number of repetitions performed, serves as an objective witness with perfect recall. Additionally, training logs allow numerous opportunities for mining information pertinent to the future performance of your clients. Even a casual review of their previous training logs can reflect training variables which produced significant improvements in performance.
Skinfold Calipers
As with training logs, utilizing a pair of calipers for periodic skinfold measurements can provide objective information in regards to a client’s progress in the gym and at the dinner table. However, unlike training logs, calipers can produce significant inconsistencies in skinfold measurements due to the use of inexpensive skinfold calipers and inconsistent user operation.
Which Calipers?
When it comes to ensuring consistent skinfold measurements, research quality calipers are a must. The calipers of choice for researchers and strength coaches are the Harpenden Skinfold Calipers. Designed in 1958, Harpenden calipers exert a constant and repeatable compression force of 10 g/mm2 over its entire jaw measuring range. Inexpensive caliper models, with their non-constant jaw tension, provide inaccurate skinfold measurements and ultimately, inaccurate body fat percentages. While Harpenden’s $400 price tag may discourage some, consider the years of service they’re going to provide. I purchased my first set of Harpenden calipers in 1989 and if not for the dirtbag who broke into my car in 2001, I would still be using that same pair today.
User Operation
The most frequently asked question concerning the use of skinfold calipers pertains to timing. Once the calipers are applied, at what point do you take the skinfold reading? Should you wait a predetermined amount of time, or should you wait until the gauge pointer comes to a stop? As you’ll soon read, the difference in timing, will produce substantially different body fat percentages.
The Best Research Study I Ever Found
Many years back, while completing laboratory work for an exercise physiology class, I learned the important lesson of consistent and repeatable measuring. The assignment, was to record skinfold measurements on ten different laboratory students, male and female. While my fellow students were taking my skinfold measurements, I noticed that each of them were recording them at different intervals after applying the calipers. While some were recording the measurements after two seconds, with the gauge needle still moving, other were waiting over thirty seconds until the needle came to a complete stop. This time difference, I believed, explained the considerable differences in measurements my laboratory mates were recording.
Bringing these different measurements to the attention of the laboratory assistant didn’t provide any answers. The best explanation the assistant could provide, was “user error.”
That same day, after a two-hour search at the university library (this was pre-internet, when research actually took time), I found the following study:
Becque, M. Daniel, Time Course of Skin-Plus-Fat Compression in Males and Females, Human Biology, 58:1 (1986:Feb.) p33
In the study, researchers wanted to determine how skinfold measurements were affected by the length of time the calipers were applied to skinfolds. Measurements were taken at the following time intervals: 2, 4, 6, 10, 15, 20, 30, 45 and 60 seconds. The researcher’s benchmark, was to determine a time period which provided a skinfold measurement free of compression and deformation.
Here are the highlights:
- “The practice of waiting for the caliper dial to stabilize before recording, results in reduced thickness estimates.”
- “If the criterion measurement is uncompressed skin-plus-fat then the reading should be made ‘as soon’ as the calipers are applied to the skin, since over 70% of the total compression takes place within 4 seconds.”
- “The absolute change in the thickness of the skinfold from application of the caliper until the end of the measurement period ranges between 0.3 mm and 4.5 mm…use of the initial or the final skinfold can result in a range of differences in predicted fat from 2-8 fat percentage points (10-50% difference).”
- “…skinfold compression conforms to a two component exponential curve. The fast component of the decay curve is representative of the expression of interstitial water from the skin-plus-fat fold. The slow component of the decay is most likely characteristic of the squeezing of the two thicknesses of skin-plus-fat until parallel. “
- “…the period of time before the caliper is read should be standardized. Based on the present data, it is recommended that this time be no longer than 4 seconds in duration”
According to the data, once the caliper’s jaws exert full pressure to the skinfold, subcutaneous water is first displaced followed by compression of the skin and underlying fat. By the four-second mark, greater than 70% of the compete compression of the skin and fat has occurred. Therefore, if a true uncompressed measurement is desired, the skinfold reading must be made within two seconds of the calipers being applied.
Worst case scenario: if you utilize measurements from compressed skinfolds, you may be underestimating your client’s body fat percentage by up to 8%. For instance, instead of being at 8% body fat, they’re actually at 16%.
FYI
- Take two measurements at each skinfold site, averaging the two readings.
- To prevent skinfold compression, take the readings in rotational order.
- Take measurements prior to exercise.
- For accurate skinfold readings, record measurements 2 seconds after applying the calipers.
- For consistent and accurate results, use the 2 second time frame for every skinfold measurement and for everyone one of your clients.
For the strength coach, employing metrics can reveal the efficacy of training and nutritional programs. Additionally, they will also give the impression to your clients that you truly care about their progress. And by utilizing metrics consistently across all clients, you ensure repeatable and predictable results.
What’s rarely measured, is even more rarely achieved.
Strengthology 