Medical-Fitness Technician
Certification Course
Part C: Assessing Medical-Fitness (LM:25-35)
Certification Course
Part C: Assessing Medical-Fitness (LM:25-35)
Supplement to Module 27:
Percent Body Fat
Percent Body Fat
This information is for explanation only and is not part of our Course.
Learning Objectives:
- Understand the concept of Percent Body Fat.
- Understand the pros and cons of %BF vs BMI+WHR.
Explanation
It's not your Body Mass Index (BMI), but your Percent Body Fat (%BF) that is relevant to your health. So, why do we focus so much on BMI? Why not just measure Percent Body Fat?
Your Body Mass Index is influenced by both your Fat Mass and your Muscle Mass (aka: Lean Body Mass, LBM), and unfortunately, your BMI does not tell you how much of your body mass is fat and how much is muscle, or in other words, your BMI does not tell you what your body composition is. Making the distinction between muscle and fat is important, because regarding your health, excess fat is bad, and "excess" muscle is good (up to a point).
However, statistics have shown that for most people (75%), Body Mass Index is an accurate indicator of their "excess body fat," and thus, it relates directly to their weight-related health risks. This is mainly because most people tend to gain fat and lose muscle over time, which is because they continue eating the same amount even though their physical activity level has been decreasing. In other words, they eat too much, and/or they do not get enough exercise.
An increase in weight (or BMI) generally reflects the process of gradually "getting out of shape." But just to make sure, the Waist-to-Height Ratio (WHR) can be used to confirm or reject the BMI as an indicator of weight-related health risk. This additional measurement helps distinguish whether your BMI value reflects mostly fat or mostly muscle. WHR is also useful because it directly measures "abdominal obesity," which is an independent health risk factor.
The public's obsession with weight is cultural and persists even though body measurements are limited and often flawed. This is why medical-fitness testing is so important. The best way to determine "weight-related" health risk is by directly testing a person's fitness level -- functional capacity -- using the exercise tests. The number on a scale or tape measure is static. A fitness score is dynamic and functional. A fitness score not only determines your health risk more accurately, it goes beyond to determine the person's true level of health and fitness.
Your Body Mass Index is influenced by both your Fat Mass and your Muscle Mass (aka: Lean Body Mass, LBM), and unfortunately, your BMI does not tell you how much of your body mass is fat and how much is muscle, or in other words, your BMI does not tell you what your body composition is. Making the distinction between muscle and fat is important, because regarding your health, excess fat is bad, and "excess" muscle is good (up to a point).
However, statistics have shown that for most people (75%), Body Mass Index is an accurate indicator of their "excess body fat," and thus, it relates directly to their weight-related health risks. This is mainly because most people tend to gain fat and lose muscle over time, which is because they continue eating the same amount even though their physical activity level has been decreasing. In other words, they eat too much, and/or they do not get enough exercise.
An increase in weight (or BMI) generally reflects the process of gradually "getting out of shape." But just to make sure, the Waist-to-Height Ratio (WHR) can be used to confirm or reject the BMI as an indicator of weight-related health risk. This additional measurement helps distinguish whether your BMI value reflects mostly fat or mostly muscle. WHR is also useful because it directly measures "abdominal obesity," which is an independent health risk factor.
The public's obsession with weight is cultural and persists even though body measurements are limited and often flawed. This is why medical-fitness testing is so important. The best way to determine "weight-related" health risk is by directly testing a person's fitness level -- functional capacity -- using the exercise tests. The number on a scale or tape measure is static. A fitness score is dynamic and functional. A fitness score not only determines your health risk more accurately, it goes beyond to determine the person's true level of health and fitness.
Percent Body Fat (%BF) VS BMI + WHtR
Bioelectrical Impedance Analysis (BIA) is a method that some scales and hand-held devices use to estimate Percent Body Fat. Although this method is convenient and affordable, it has a plus/minus range of 4%, which makes it not precise enough for clinical or research purposes, or even for personal application in a fitness training or weight-loss program.
The more accurate methods for measuring %BF (e.g., underwater weighing, multi-site skin-fold measurements, and x-ray (absorptiometry) are complicated, expensive, and require special equipment and skilled personnel.
In contrast, BMI is easily calculated from two simple measurements (height & weight), which are accurate and reliable. When coupled with WHR, another simple and accurate measurement and calculation, using BMI & WHR becomes a valid assessment of health risk that can be tracked easily and accurately, making it most appropriate for use with the general public in a community-based clinical setting.
The few clients (15%) that BMI+WHR may miss regarding their weight-related health risk are your "skinny-fat" clients. These are people who are of normal weight and have a normal waist circumference, but have so little muscle that their body composition by percent is unhealthy. BIA would probably detect this situation, but would often be met with strong objection from the client. Fitness testing detects all "skinny-fat" cases, and the client readily accepts the fact that they are not fit, even though they are not "overweight."
General fitness testing will become the ideal measurement of health as more medical-fitness technicians are trained and more medical-fitness services become available. Until then, we are stuck having to measure and explain body weight and waist circumference, or even percent body fat, in relation to health risk, rather than simply measuring functional capacity (fitness) alone.
The more accurate methods for measuring %BF (e.g., underwater weighing, multi-site skin-fold measurements, and x-ray (absorptiometry) are complicated, expensive, and require special equipment and skilled personnel.
In contrast, BMI is easily calculated from two simple measurements (height & weight), which are accurate and reliable. When coupled with WHR, another simple and accurate measurement and calculation, using BMI & WHR becomes a valid assessment of health risk that can be tracked easily and accurately, making it most appropriate for use with the general public in a community-based clinical setting.
The few clients (15%) that BMI+WHR may miss regarding their weight-related health risk are your "skinny-fat" clients. These are people who are of normal weight and have a normal waist circumference, but have so little muscle that their body composition by percent is unhealthy. BIA would probably detect this situation, but would often be met with strong objection from the client. Fitness testing detects all "skinny-fat" cases, and the client readily accepts the fact that they are not fit, even though they are not "overweight."
General fitness testing will become the ideal measurement of health as more medical-fitness technicians are trained and more medical-fitness services become available. Until then, we are stuck having to measure and explain body weight and waist circumference, or even percent body fat, in relation to health risk, rather than simply measuring functional capacity (fitness) alone.
Percent Body Fat
Percent Body Fat (%BF) can be estimated (+/- 4%) through Bioelectrical Impedance Analysis. BIA devises pass a small electrical current through the body, which is not detected by surface or internal neuro-sensors. (The client does not feel anything.) Different body tissues: fat, muscle, bones, organs, etc., contain different amounts of water, and therefore transmit (or impede) the electrical current differently to give tissue-specific results. The different speeds at which the electrical current passes through the body are used to calculate the body's composition of fat and lean body mass.
However, even if technology in BIA continues to improve and measuring %BF becomes more accurate, it would still be an indirect method to measure health risk and fitness levels. Direct fitness testing is required to determine the functional capacity of the muscles and the condition of the cardio-pulmonary-vascular system that supports them.
It is the opinion of the OptiHealth Institute that BIA is not much more useful than an "eyeball" assessment of a person's body composition. You can use the charts below to learn from each client how to assess a person's approximate %BF.
However, even if technology in BIA continues to improve and measuring %BF becomes more accurate, it would still be an indirect method to measure health risk and fitness levels. Direct fitness testing is required to determine the functional capacity of the muscles and the condition of the cardio-pulmonary-vascular system that supports them.
It is the opinion of the OptiHealth Institute that BIA is not much more useful than an "eyeball" assessment of a person's body composition. You can use the charts below to learn from each client how to assess a person's approximate %BF.
A general guideline for a healthy %BF is 10-20% for men and 15-25% for women.
Individuals with high levels of fitness, above "generally healthy," have lower %BF compositions:
< 10% for men and < 15% for women due to increased muscle mass -- more than those pictured above.
< 10% for men and < 15% for women due to increased muscle mass -- more than those pictured above.