The important numbers in fitness and exercise

Measuring Your Progress: The Important Numbers
A.   Confusing or misleading numbers
1.    Total body weight
Your body weight is composed mainly of the weight of your internal organs, your bones, your muscles and your body fat.  The number that you see on the scale is the sum of the weight of all of those.  When we measure the body composition fitness level, we are mostly measuring the person’s muscle mass and body fat, not the internal organs and bones.  The weight of your internal organs and bones is out of the equation to measure your fitness.  In any case, there is not much you can do about their weight.  Note then that your total body weight includes two components that do not measure your fitness level.  What we want to focus on is the weight of your muscle mass and your body fat.  However, total body weight does not distinguish between muscle mass and body fat.
Let’s say John weighs 170 lbs.  Is he fit?  We don’t know.  First, we don’t know how tall he is.  The weight of the bones is the largest contributor to total body weight.  Therefore, the height is the most important factor to interpret the total body weight.  Gender is also another factor, but we already know that one.
Now, let’s say that John is 5’9”.  Is he fit?  We still don’t know.  John may have a huge beer belly or he may be an athlete with a lot of muscle mass and almost no fat in his body.  But we don’t know from the total body weight and his height.
Now, let’s say John takes some laxatives and diuretics one day.  The next day he weighs five pounds less.  Is he in better shape now?  Definitely not.  He just lost weight due to the effects of the laxatives and the diuretics.  He will gain it all back as soon as he gets back to normal eating without the laxatives and diuretics.  In fact, John may be in worse physical condition now.  Boxers use laxatives and diuretics to fool the scale the day before a fight, with the risk of being in worse condition at the time of their fight.
Therefore, total body weight does not provide us with a great deal of information on the fitness level of a person unless we also know his or her gender, height, and body composition.  Total body weight is not that useful and not the best measurement of the fitness level of a person.


2.    BMI
There is a ratio called the Body Mass Index (“BMI”) that is generally used to determine whether someone has a normal body weight.  The BMI is a statistical measure of healthy weight.  There are different statistics for men and for women.  Therefore, it also takes into account gender.  Generally, a person with a BMI of less than 18.5 is considered underweight.  Between 18.5 and 25 is considered to be normal.  From 25 to 30 is considered overweight, and over 30 is considered obese.
However, BMI has a huge limitation: it does not distinguish between lean muscle mass and body fat.  Therefore, people with low levels of body fat and a lot of muscle mass, like athletes, appear as overweight using the BMI.  On the other hand, a person with a lot of belly fat may appear as having a normal BMI.
As an example, the following celebrities are classified as “overweight” using the BMI:
Weight (lbs)
George Clooney
Tom Cruise
Denzel Washington
Will Smith
Keanu Reeves
Brad Pitt
Lebron James
Johnny Depp
Dwayne Johnson (“The Rock”)
According to the BMI, The Rock is obese and Lebron James is overweight.  That proves that the BMI is not a reliable measure of fitness.
Now let’s take a look at the important numbers.  The following numbers will provide you a better idea of your physical and cardiovascular fitness level.


B.   Numbers that provide you with a better measure of your fitness and cardiovascular level


1.    Body fat percentage
The body fat percentage is a ratio of the total fat in your body divided by the total weight.  It tells you how much of your body weight is fat.  This is the only measure that provides a direct indication of physical fitness because it measures your body composition excluding the height and total weight factors.  It tells you how much fat you have in your body independent of your gender, height and total body weight.  This is the number you should be looking for to measure your physical fitness level and your progress.
According to the American Council on Exercise,[1]your physical fitness level is classified by your percentage of body fat as follows:
Essential Fat
            There are different methods to measure your body fat percentage, but the most popular and commonly used is the skinfold method.  You can find a body fat calculator and the explanation of the skinfold method in the American Council on Exercise website link on the footnote below.  You can measure your body fat every month to track your progress.


2.    Body measurements
Another set of numbers that is useful to determine your physical fitness level and progress are the body measurements.  These include the circumference of your chest, waist, hips, arms and thighs.  Most of us are familiar with the measurement of our waist, and most women are also familiar with the measurement of their hips.  This is what we see every day in the pants size and the dress size.  Physical fitness condition is correlated with the size of the waist and with the ratio of the waist to the hips.  You can take these measurements every week or every month to track your progress.


3.    Difference in density of muscle and fat
When we are measuring physical fitness it is important to note that there is a difference in density between muscle mass and body fat.  Density is the ratio of the mass of a substance per unit volume.  It will tell you how much a specific volume of a substance will weigh.
Muscle has a density of 1.06 g/ml, or 0.038 lbs/in3.  Body fat has a density of 0.9 g/ml, or 0.033 lbs/in3.  Therefore, muscle mass is 18% more dense than fat.  That means that a person with a low body fat percentage will weigh more than a person of the same size but with a higher body fat percentage.  It also means that a person with a low body fat percentage will be a smaller size than a person of the same weight but with higher body fat.
This is important to keep in mind, because it means that if you are working on getting fit, you may stay at the same total body weight or even increase it a little bit while you drop your pants size.  This may probably happen at the start of your plan to get into shape.  During the first few weeks exercising, your muscles may start to develop and grow, while you may not lose fat as quickly.  In that case, you may stay at the same weight, or even gain a little extra weight, while at the same time your clothes will start to feel loose.


4.    Resting heart rate
The resting heart rate is a good way to measure your level of aerobic or cardiovascular fitness.  When you do aerobic or cardiovascular exercise, like running, swimming, cycling or other kinds of exercises for long periods, you are exercising your heart.  As with any other muscle, the more you exercise your heart, the stronger and more efficient it will get at its job.  Therefore, aerobic exercise will make your heart more efficient.  Your heart will pump the blood your body needs with less beats per minute (“BPM”).  For most people, the resting heart rate will be between 60 and 90 BPM.[2]  Athletic training can lower your resting heart rate by 10 to 20 BPM.[3]
Therefore, before you start your fitness program, measure your resting heart rate to establish your baseline.  After that, measure it periodically to find out the progress of your cardiovascular fitness.
C.   Conclusion
To measure your physical fitness level, take a close look at your body fat percentage and your body measurements.  To measure your aerobic or cardiovascular fitness, take a close look at your resting heart rate.  Don’t get obsessed with your total body weight.  What you read on the scale every day is not the best indicator of your physical or cardiovascular fitness or your progress.  It is another number to look at, but not the most important one.