The Importance of Tracking Body Composition in Athletes

By Bob Alejo and Dr. Jordan Moon

I’m surprised, but not that much, that there is seldom any rhetoric or higher level of discussion about body composition. Granted, it’s all about sports performance results. But what about BETTER sports performance results? We can gain some insights on this by learning about norms. There’s a good amount of research on athletes that includes at least body weight, regardless of the purpose of the study. For some studies, body weight is crucial when scaling for strength and power. And, as we read more about running speed, we realize that mass is important to speed. Certainly, the engine producing that speed is important as well.

There are plenty of online photos showing “before” and “after” for athletes, as freshmen and then later, yet almost nothing showing “before” and “after” for lean mass, fat mass, and body composition changes. There is no argument that those physical changes could result in more lean tissue loss than necessary, which would certainly affect the efficacy of strength and power acquisition. Not taking body composition measurements during these transformations means that it is an all-out guess for caloric addition/restriction or protein intake. In addition to how much an athlete can squat, it would be great for practitioners to show body-weight-to-strength ratios, along with body composition information. Now that would be comprehensive! I know other coaches would love to see that.

Don’t kid yourself: Body weight and body composition matter! Here, as a follow-up to my last conversation on testing methods with body composition expert Dr. Jordan Moon, I ask him more questions about body composition for athletes.

Bob Alejo: What’s the general relationship between body composition and performance?

Does it even matter? Some would argue that it’s all about results, but that’s certainly a myopic view. How you obtain the information is probably more important than the results, of course. I’ve heard BOD POD testing horror stories: not testing for hydration, taking the test at different times of the day over a period, taking the test less than 24 hours after a hard workout. Sure, that’s no fault of the BOD POD—it just gives you a number—but, under those circumstances, you’d be better off getting your body composition guessed at the State Fair booth!

How often do you test? Both the method used and tracking over time can mean the difference between accurate and not accurate, within reasonable limitations. Most methods already have a standard of error, so there’s no use making it worse or making it so taking some tests overall is a waste of time. And remember, body comp is not just about performance, it’s about health!

Dr. Jordan Moon: In general, the simple answer is that “body composition is an apparent function of the physical task,” and the closer an athlete’s body composition is to the ideal body composition for their sport, the better their performance will be.¹

In general, the closer an athlete’s body composition is to the ideal body composition for their sport, the better their performance will be, says @DrJordanMoon. Share on X

Specifically, by looking at body composition differences between types of elite athletes, we can get an idea of optimal fat, lean, and total mass values for a sport and position. With more athletes now being measured by dual-energy X-ray absorptiometry (DXA), we can build a bigger database for professional, collegiate, and even youth athletes for all types of sports. Another advantage of looking at DXA data for optimal body composition comparisons is that you can look at lean and fat mass values of the arms, legs, and trunk, in addition to whole body. This allows for some unique comparisons between athletes. However, DXA manufacturers have not integrated athlete data or the capacity to compare measurements to other athletes into their software or reports. This limits the ability of athletes, coaches, trainers, nutritionists, physicians, etc., to make actionable decisions that help improve performance.

Fortunately, there are some new software programs/apps gaining traction that allow for the comparison of DXA data to other athletes. One such program is FitTrace, which allows you to:

• Track and report body composition over time.
• Provide access to results for nutritionists, trainers, coaches, etc.
• Compare with professional athletes by sport and position.

However, not all athletes or programs may have access to a DXA machine, which makes detailed and accurate comparisons to elite or pro athletes more complicated. There are some books and published articles that have data from elite athletes using other techniques such as underwater weighing, anthropometrics/skinfolds, and the BOD POD. However, the use of data from one method, such as underwater weighing, compared to another method, such as skinfolds, adds additional errors when comparing athlete data, and it may not allow you to make actionable decisions with confidence.

Another focus of body composition and performance should be on tracking changes over time. This concept is more accessible, as the only requirement is a reliable and valid measurement tool. In theory, as long as your method gives you correct measurements, you can use that data to determine potential improvements or decrements in performance. More importantly, tracking changes in fat, lean, and body mass allows for a quantifiable assessment of the success of a training and/or nutritional intervention. For example, if an athlete needs to lose body fat while preserving as much lean mass as possible, and they are following a strict off-season training and nutritional program, having accurate fat and lean mass measurements before and after the off-season is fundamental when assessing the athlete’s adherence to the program and/or the quality of the program.

Tracking changes in fat, lean, and body mass allows for a quantifiable assessment of the success of a training and/or nutritional intervention, says @DrJordanMoon. Share on X

Researchers and sports scientists are now focusing on identifying other relationships between performance and body composition. Some areas of current research on athletes and performance are directed toward body composition and injury risk, lean and body mass imbalances, lean/muscle mass loss after an injury, return to play after an injury, and optimal strength-to-lean-mass ratios for specific muscles and sports movements (bat swing, jumping, sprinting, etc.). The next several years are going to be very exciting. We will start to get a better picture of the direct relationship body composition has to overall performance and health in athletes.

Beyond the general idea of body composition being a function of a physical task, we are also becoming more aware of how specific body composition values, such as fat and lean mass, play a role in both performance and health. It’s intuitive that an offensive lineman requires a greater amount of body fat compared to other positions, because their task is to block heavy defensive linemen. The heavier they are, the easier it is to stop a defender, but there is also a need for speed and strength. Knowing the correct fat-to-lean ratio for optimal performance and strength is valuable here and also somewhat intuitive, but do you know the ideal ratios? You know you want a heavy, fast, and powerful lineman, but did you know offensive linemen in the NFL have 2.5 times more lean mass than fat mass? Compare this to wide receivers or defensive backs, who have a ratio of around seven.

Another well-documented finding is that the performance of speed and jumping athletes is directly related to their power-to-mass ratio. Those who can generate the most muscle power at the lightest body weight can run faster and jump higher, but this is also relatively intuitive. If two athletes have the same muscle power and one is slightly lighter, then that athlete can jump higher and run faster because they are moving less total body mass. The impact of body composition here is not only optimizing fat content to be low, but also optimizing muscle mass to be powerful without being too large, which can be altered by specific training and nutrition programs.

For distance runners, research has found that skinfold (fat) thicknesses in the lower body can predict 1,500-meter, 10,000-meter, and marathon times. Those with more lower body fat don’t run as fast and finish slower. Like sprinting and jumping athletes, distance runners can benefit from having optimal body-fat-to-lean-mass ratios (% fat). Also, when comparing the most elite sprinters and distance runners, there doesn’t appear to be any difference between fat values, which indicates that, at the elite level, all athletes for particular sports have almost identical body composition values.

What about body composition and injuries? Having the lowest possible body fat/weight for athletes who sprint, jump, or run moderate-to-long distances does appear to enhance performance, but there may also be a risk for more injuries and overall health concerns. Researchers have found that distance runners who have more muscle mass tend to have fewer stress fractures. Distances runners who have more muscle and less fat have better performances and are less likely to have fractures compared to similar runners with the same or lower body weight, but with less muscle and more fat. So, just having low body fat and a low body weight is not enough for runners to reduce injuries and perform at their best. Understanding the optimal lean mass and fat mass for the upper and lower body, as well as total body mass, is fundamental for the success of any training and nutritional programs for not only runners, but all athletes.

Understanding the optimal lean and fat mass for the upper and lower body, as well as total body mass, is vital for the success of any training & nutritional programs, says @DrJordanMoon. Share on X

Finally, there are several health-related and performance concerns for having too little body fat. This is a highly complicated area with several factors all impacting each other. In summary, lower-than-optimal body fat values can have just some of the following effects on an athlete:

• Unhealthy eating habits and malnutrition.
• Loss of energy and focus.
• Increased stress and impaired immune system.
• Abnormal hormone levels.
• Reproduction system problems (females).
• Reduced bone health and increased fracture risk (lower bone mass/density).

All of the above can significantly impact both performance and health, and they are specifically a concern for weight-sensitive athletes in sports such as:

• Gravitational: running, jumping, skiing, cycling, climbing, etc.
• Weight Class: wrestling, judo, boxing, martial arts, powerlifting, jockey, etc.
• Aesthetically Judged: bodybuilding, figure skating, diving, cheerleading, etc.

Body composition variables, such as lean and fat mass, and their relationship to athletic performance is highly dependent on the specific athlete, sport, and position, but also the athlete’s competition level/ability (recreational, collegiate, professional, etc.).

Bob Alejo: Should performance focus on body weight, fat loss, lean tissue gain, or body composition?

Dr. Jordan Moon: This is where research and application separate, and this is currently the largest gap in the field of body composition and performance. There are hundreds of great research papers and a recently published body composition book focusing on health and performance in exercise and sport. However, this information is not easily accessible for most athletes, coaches, trainers, sports scientists, nutritionists, physicians, etc.

Practitioners often look at body composition as something easy to do and utilize because of the simplicity and accessibility of measurements. However, over the last 15+ years, I have observed a significant lack of understanding and confidence from most practitioners when it comes to interpreting body composition data and using it in programming. What I see most often are practitioners simply looking at two variables, % fat and fat-free mass, and tracking changes to see if an athlete is losing fat, gaining muscle, losing muscle, or gaining fat.

Even with this basic approach, there are many practitioners who are still not sure what to do. However, this isn’t really their fault, as practitioners in the field don’t have the time or training to read hundreds of body composition research papers or interpret graduate-school-level textbooks to find actionable information that they can use for their athletes. So, what are their options, other than contacting researchers who work in this area?

As of now, the answer is to learn more about body composition, read the research and the books, and find the content you need to make informed decisions about your data and athletes. It’s a double-edged sword type of situation. There are very few expert practitioners who work with athletes and have a great handle on body composition and application. Most experts are researchers. There will be a good deal of work initially to understand everything, but if someone can solidify themselves as a true expert in the field by using scientifically supported interpretations of accurate data with developed protocols for training and nutritional interventions for athletes, they will be the leading edge of the sword, while carving a unique and needed position for themselves and others who follow.

Track body composition data often and with intention. Don’t just measure body composition because you can. Do it with purpose, says @DrJordanMoon. Share on X

As I stated earlier, there are some programs and apps that attempt to bridge this gap, but the actual creation and implementation of a program requires knowledge of body composition, as well as exercise training and/or nutrition. My simplest suggestion of what to focus on for performance and body composition includes the areas discussed earlier:

• • Compare your athletes to other athletes using published data and the same method used in the publication (article or book).1.
    • Create a training/nutritional program that will support a change in body composition to more closely match others in their sport or those who are the next level up (college, pro, etc.).

    2.

    Use caution when working with children and adolescents—that’s another discussion completely.

3. Utilize as much information as possible to compare. If you can get a DXA measurement, you can look at segmented (arms, legs, upper body, lower body) ratios of lean, fat, bone, and total mass, as well as utilize software/apps for easy comparisons, creating reports and graphs, and data management and sharing.

• • — Anthropometric measurements (skinfolds and circumferences) are also highly available for athlete comparison and you can take them from multiple locations around the body.

 

• — Limited data is available for athletes to compare themselves to other athletes using bioimpedance data, as well as having a wide range of machines and equations, making athlete comparisons questionable at best.

• • Track body composition data often and with intention. Don’t just measure body composition because you can. Do it with a purpose.1.
    • Sport-/athlete-specific transitional periods (pre-season, in-season, postseason, etc.).
      • — For example: Right before a season, mid-season, and right after a season.
        • • This can help identify any loss of lean or fat mass, typically observed due to highly competitive and energy-demanding activity. You can implement appropriate training and nutritional interventions to offset losses in lean and fat mass that may hinder performance.

     

2. You should measure at-risk athletes for low body fat often and interpret and share their results with caution.

• • — This is a highly sensitive subject for many athletes and using the wrong language and/or telling someone their results can increase their chances of developing an eating disorder and/or body image issue.

 

• — The lower limits for % fat depend on the methods used (DXA, skinfold, etc.), but the general acceptable lower limits are:
  • • Men: 1–9% fat
    • Women: 10–18% fatA.
      This is highly dependent on multiple factors and specific to each individual. You may have one athlete on the same team at the lower end and have no issues, while another athlete is closer to the higher end with multiple symptoms.

Bob Alejo: Can skinfolds be an accurate measure of fat loss or lean tissue gain? Personally, based on convenience and the error of measurements with poor protocols with other methods, I prefer skinfolds. At the least, I support performing skinfolds and perhaps one other test for sure. Changes in millimeters of thickness (mm) from test to test say something. Of course, good protocol makes it easier to discern what you are seeing.

Dr. Jordan Moon: The answer is yes and no. It all depends on the person conducting the measurements, the equipment, and the preparation of the athlete. Below are some guidelines when performing skinfold measurements:

• Use a quality caliper that is valid and reliable (calibrated and checked for calibration regularly).
• Use the same calipers every time for the same athlete.
• Measure the correct and exact same locations each time with the same approved technique.
  — This requires a trained technician (more on this later).

• Measure the athlete at the same time of day in the same conditions (before training, preferably).
  — If using body weight for any calculations (like fat-free mass), perform measurements with the athlete fasted in the morning and normally hydrated.

The biggest factor when it comes to getting accurate measurements for skinfolds is the training and quality of the person taking the measurements. The most comprehensive skinfold training is through The International Society for the Advancement of Kinanthropometry. However, the training is expensive, with limited availability. ISAK has a great training program if you are looking to compare your athletes to other athletes around the world and/or want to learn how to take circumferences and other anthropometric measurements in addition to skinfold measurements. However, you may not need it if you simply want to track changes in fat and lean mass. Using the ACSM standards is also sufficient.

The other issue when using skinfolds for tracking lean and fat changes is the equation used to convert skinfold thicknesses to fat and lean tissues. I like using raw skinfold data when tracking changes because the units are raw measurements in millimeters. There are athlete-specific equations if you are looking to compare your athletes to others, but you would need to find the paper or book with the normative data and see what equation you should use to compare athletes.

However, when it comes to tracking changes, I always recommend the Jackson and Pollock three- or seven-site equations^2,3 because they don’t use anything other than age and skinfold thickness to calculate % fat, so changes in body weight due to hydration do not impact the % fat values, but they will alter fat-free and fat mass values. Thus, if you are interested in fat mass and fat-free/lean mass, you need to understand body weight variability and try to control for normal hydration.

I recommend this link, which calculates the data for you using the Jackson and Pollock equations. However, you will need to follow the ACSM guidelines and know what sites to measure if you only measure three. I always recommend measuring all seven because you can look at regional changes in fat thickness while having more comprehensive calculations of % fat and other variables. Seven sites may represent a more accurate overall change in fat compared to just three.

Body water, which is the largest and most variable component in your body, often causes changes in body mass and lean mass throughout the day and from day to day, says @DrJordanMoon. Share on X

Finally, skinfold measurements only represent subcutaneous fat, which is the fat under your skin that accounts for most of your total body fat. Lean tissue changes are not directly measured; instead, they are indirectly measured by subtracting your fat mass from your body weight. Therefore, detecting changes in fat may be more accurate than changes in lean mass. Lean mass also includes body water, which is the largest and most variable component in your body and often causes changes in body mass and lean mass throughout the day and from day to day.

Bob Alejo: Is there any value in using the body mass index (BMI) for athletes? Look, sometimes folks don’t fit in the BOD POD, and they can’t be skinfold tested. So, BMI might be your next choice. Keep in mind that you should most likely evaluate other measures (speed, strength, power, team/position athletic measure comparisons) because, as you will see, BMI is not what it’s cracked up to be for athletes.

Dr. Jordan Moon: Since BMI is just the mathematical expression of the proportions of height and weight, it doesn’t tell us anything about actual body composition, such as fat or lean tissue masses. It is IMPOSSIBLE for you to estimate fat or muscle mass accurately using only height and weight. The problem is that BMI is used to classify “normal” people as being underweight, normal weight, overweight, or obese. This is an issue for many athletes because they typically have larger lean mass values, which increases their total mass and, consequently, their BMI.

BMI is just the mathematical expression of the proportions of height and weight—it doesn’t tell us anything about actual body composition, such as fat or lean tissue masses, says @DrJordanMoon. Share on X

For example, all pro bodybuilders are considered obese, or even morbidly obese, due to their increased muscle mass, even though they have around 5% body fat when competing. Nearly all strength and power athletes have elevated BMIs that classify them as being overweight or obese because they have more lean mass than the “normal” population. Therefore, you should never use BMI to classify men or women who have greater than average muscle mass as being “overweight” or “obese” in terms of excessive body fat. In other words, if someone has ever regularly strength-trained, the BMI classification as the World Health Organization (WHO) defines it (below) is no longer applicable.

In agreement with this concept, the WHO states: “BMI values are age-independent and the same for both sexes. However, BMI may not correspond to the same degree of fatness in different populations due, in part, to different body proportions.”

Theoretically, BMI should represent body fatness, but only in nonathletes. Numerous research studies have proven this point by showing that BMI is a poor predictor of actual fat in athletes. So, is there any use for BMI then?

The WHO claims that: “The health risks associated with increasing BMI are continuous, and the interpretation of the BMI grading in relation to risk may differ for different populations.” Meaning, we still don’t know how BMI relates to health, but a higher BMI could increase health risks. Are athletes with higher BMI due to more lean mass (not fat) at a greater risk for poor health and disease? Is it not just about too much fat, but too much total mass, regardless of the tissue?

Research actually shows that the lowest (all-cause) risk of mortality (death) rate is in people with a BMI between 25 and 30, who are considered “overweight.” Research also indicates that cardiovascular disease risks are lower in those with a BMI between 25 and 30.

Research has even shown that a little extra fat is helpful. A case in point: During a fall, extra fat offers more protection for your bones. Additionally, research has found that individuals with a little more fat may heal faster after surgery and are less likely to get infections. An article in 2010 found that when controlling for health behaviors and sociodemographic factors, both overweight and Class I obesity reduced the relative risks (RRs) of death compared to a BMI of 18.5–24.9. There are many more articles that support these findings, but also studies that suggest an increase in mortality in people with a BMI under 20 and over 24.9.

So, what does this mean for athletes? For those with BMIs 20–29.9, we can’t really make a definitive conclusion about health and mortality since the data is not in agreement even in a “normal” population (nonathletes). So, it’s safe to say that athletes who have slightly more lean mass than normal people with BMIs in the “overweight” range shouldn’t worry about increased health risks, including cardiovascular disease. Still, research suggests that health risks associated with BMIs are nonlinear, meaning that deaths occur much more rapidly at both lower and higher BMIs (under 20 and over 30), implying a relationship between health and mortality and being obese and underweight. As stated earlier, many strength and power athletes have a BMI over 30.

However, there isn’t enough evidence or data using accurate body fat measurements along with mortality and health data in a normal or athlete population to determine if a BMI over 25, or over 30, increases someone’s health risk, regardless of their BMI being high due to either muscle or fat. Simply put, too much fat or too much muscle could lead to a greater health risk, but we really don’t know for sure because we don’t have accurate body fat and lean mass data along with health and mortality data in any population. With that said, there are known risks of being large, regardless of the mass being fat or muscle.

Sleep apnea, specifically “obstructive sleep apnea,” is a potentially fatal condition that can be caused by too much upper body mass (fat or lean). The larger mass in the neck and trunk puts more pressure on the airway and lungs, and it can prevent big athletes from getting a good night’s sleep and the oxygen their body needs to recover. Other symptoms can include fatigue, high blood pressure and other cardiovascular issues, diabetes, metabolic syndrome, medication and surgery complications, etc. Fortunately, larger athletes can reduce sleep apnea (and related symptoms) by using a continuous positive airway pressure (CPAP) machine.

Several, if not all, elite strongman athletes use CPAP machines. These athletes typically weigh well over 300 pounds, with many weighing in at 400 pounds or more. Even at a height of 6’9”, someone weighing 400 pounds will have a BMI of 43, which is Class III obesity, regardless of their body fat. BMI alone, in this case, could be useful for identifying athletes who may benefit from using a CPAP at night. I suggest using a BMI of >30 as a good starting point to begin watching for sleep apnea. For athletes with BMIs over 35, I would consider consulting with their doctors and having them use a CPAP at night, and both their health and performance could improve.

The use of BMI alone for athletes with low amounts of lean mass and body fat could serve as an easier way to track changes because you only need to measure height once and body weight. Share on X

Another suggested application for BMI in athletes would be for those who have lower amounts of lean mass and are at risk for low body fat, such as endurance athletes. As stated earlier, because there are greater health risks in these athletes, it is important to monitor their body composition. The use of BMI alone could serve as an easier way to track changes in these athletes because you only need to measure height once (if fully grown) and body weight.

Using BMI here could be valuable, but you are only looking at changes in body mass, so is there really an added benefit in calculating BMI? I would say yes, as several research studies looking at endurance athletes, from recreational to elite, have reported average BMI values no less than 19 for men or women. Therefore, I suggest for those at-risk athletes, as mentioned earlier, calculating BMI and using a low cutoff of 19 could serve as a simple and early detector for possible low body fat or lean mass.

If you need one, I recommend this online BMI calculator.

Since you’re here…
…we have a small favor to ask. More people are reading SimpliFaster than ever, and each week we bring you compelling content from coaches, sport scientists, and physiotherapists who are devoted to building better athletes. Please take a moment to share the articles on social media, engage the authors with questions and comments below, and link to articles when appropriate if you have a blog or participate on forums of related topics. — SF

References

1. Moon, J.R., Tobkin, S.E., Costa, P.B., et al. “Validity of the BOD POD for assessing body composition in athletic high school boys.” Journal of Strength and Conditioning Research. 2008; 22(1): 263–268.

2. Jackson, A.S. and Pollock, M.L. “Generalized equations for predicting body density of men.” British Journal of Nutrition. 1978; 40: 497–504.

3. Jackson, A.S., Pollock, M.L., and Ward, A. “Generalized equations for predicting body density of women.” Medicine & Science in Sports & Exercise. 1980; 12: 175–182.

Since you’re here…
…we have a small favor to ask. More people are reading SimpliFaster than ever, and each week we bring you compelling content from coaches, sport scientists, and physiotherapists who are devoted to building better athletes. Please take a moment to share the articles on social media, engage the authors with questions and comments below, and link to articles when appropriate if you have a blog or participate on forums of related topics. — SF

Dr. Moon is an experienced researcher and advisor in the field of human body composition analysis and sports supplements. He has presented over 50 lectures at multiple scientific conferences and events both nationally and internationally, and has published more than 140 research articles and abstracts in dozens of journals. Additionally, Dr. Moon has written a book chapter and published a book in the areas of sports nutrition, supplements, exercise science, body composition, body water, and changes specific to age, fitness level, and type of athlete. Dr. Moon is also a co-founder and the Chief Science Officer at FitTrace.com, a body composition management and analysis app. He currently holds faculty positions at Concordia University Chicago and the United States Sports Academy.