One of the best ways to tell if you’re on target with your fitness and nutrition goals is to keep track of the size of your body.
Not your body weight. Your body size.
My favorite way to gauge whether I’m heading in the right direction is to try on my motivation jeans. But there are other ways too. Some better than others.
The bathroom scales; they lie (as do your husband and best friend when you ask them if you look like you’ve lost weight!). And they can fluctuate by as much as 4 or 5 pounds in a single day, depending on whether your stomach is full or empty and how well hydrated you are. Personally, I’ve sworn off of them!
BMI (body mass index). Although BMI used to be the standard doctors relied on when determining whether a body was a healthy size, because it’s based only on height and weight (BMI = weight(kg)/height(m)2 ), it provides no information about body composition, as such. That is whether your body has lots of muscle and very little fat or lots of fat and very little muscle. Obviously, the former is better than the latter!
Although it’s a good general predictor of your risk of cardiovascular disease, waist-to-hip ratio is really no better for gauging your fitness level.
What you really want to know, when evaluating your overall health and fitness, is what percentage of your total body mass is accounted for by fat? The lower this number is (within reason), the better you’ll look and the healthier you’ll be.
But how do you measure body fat?
- Total body water immersion. This is not something you do in the bathtub. Hospitals and weight loss clinics sometimes provide this service, which works by calculating the volume of water your body displaces.
- Use a scale that calculates it. Called an ‘impedance’ scale, it calculates percent body fat by shooting a signal upwards through your (bare) feet and measuring how quickly it’s transmitted to your head and back. Transmission rate is affected by your body’s composition, traveling more quickly through muscle than fat. Impedance scales can be found in most health and fitness clubs and can even be purchased for home use. Their accuracy depends on the subject being properly hydrated. Some allow you to specify whether your physique is ‘normal’ or ‘athletic’. When I press the ‘athletic’ button, my body fat drops by 2-3%.
- Have a professional measure your skin fat folds using special calipers. You can’t do this one on your own. Although one of the most accurate ways of determining body composition, it relies on taking measurements at very specific places on the body. The use of landmarks helps, but it’s still difficult to repeat measurements within a session, let alone over sessions weeks or months apart. Ask your professional what their ‘measurement repeatability’ looks like.
- Use a statistically determined relationshipbetween a series of girth measurements and percent body fat. This approach is based on regression analysis (if math is not your thing, avert your eyes now), in which thousands of individuals were subject to a whole bunch of girth measurements, then immersed in water to determine their true body composition. An equation is derived from the measurements that taken together, best predict per cent body fat. There is usually an error term associated with the equation, meaning that it’s correct plus or minus 2-3 %.
The last one is my preferred method. It’s quick (the equation I use requires just three measurements, plus weight and height), requires only a measuring tape and is easily repeatable. I caution my clients that the number I give them is not necessarily their true per cent body fat (my equation has a +/- 3% error in it’s estimate). But if we only measure every 6 weeks and we see a reduction in the number, we know that their exercise and nutrition program is working!Whichever method you use, remember that you’re looking for directional change over time. Don’t measure too frequently; it may take your body awhile to respond to changes in activity level and nutrition.
How do you track the changing size of your body?
Do you obsess over the numbers or use how you feel as a guide to measuring progress?