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Monitoring Body Composition in Young Athletes: A Guide for Parents & Coaches

Fitnescity, Inc

For parents and coaches, DEXA scan results can provide quantifiable data on their youth’s health and fitness level, disease risk, and training program effectiveness.

At 6-foot-3 and 375 pounds with a BMI of 46.9, Michael Onwenu is “severely” obese. 

That’s according to official parameters set by the Centers for Disease Control and Prevention (CDC), anyway, which relies on the Body Mass Index (BMI) to screen for overweight or obesity. 

But in addition to being “severely obese,” Onwenu is a professional athlete. And not just any athlete—he’s the strong, fast, and fit offensive lineman for the New England Patriots who has been touted as “one of the best rookies in the NFL.” 

Onwenu’s misleading classification as obese demonstrates the limitations—and potential harm—of using BMI as a measure of health. As a high schooler growing up at Cass Technical High School in Detroit, Onwenu was nicknamed “Big Mike” and was constantly being questioned for his weight. Many coaches and recruiters expressed concern that he was too big and assumed he must not be training hard enough. And Onwenu, as any teenager would have, was bothered by assumptions made about him based on his weight and felt uncomfortable in his body. 

It wasn’t until Onwenu was recruited for the football team at the University of Michigan that people stopped questioning his health. Instead of scale weight or BMI, the nutrition and weight staff at Michigan checked Onwenu’s body composition, using a DEXA scanning technology to assess his body fat percentage and bone density. 

The results? Far from being obese, Onwenu was as healthy as any all-star athlete on the offensive line. 

“The assumption is that being that big, you have to be carrying a lot of fat,” offensive line coach Ed Warinner explained in an interview with Telegram & Gazette. “His [readings] were as good as anybody on the O-line. It’s his bone density, his thickness, his muscle mass, that’s what’s incredible on him. It’s not that he weighs 360 or whatever because he has 30 pounds extra fat that he could lose.” 

Onwenu’s experience highlights the importance of looking at overall body composition—and not scale weight or BMI—to gain a more accurate picture of the health, fitness, and disease risk of young athletes.  

How body composition influences the health & fitness of young athletes 

Body mass index—which represents the relationship between a person’s height and weight—has long been used as a tool in youth sports to determine whether athletes are too heavy for their height to perform at optimal levels. The issue with BMI is that by neutralizing the impact of height on body weight, it makes no distinction between body fat and lean muscle mass. That’s why a muscular, fast, and active athlete like Michael Onwenu could have a much higher BMI than a sedentary individual with a lot of excess belly fat. 

In terms of assessing health, fitness, and disease risk, body composition is a far more accurate measure than BMI. Broadly speaking, body composition is a measure of the total amount of fat, muscle, bone, and water in your body. In the fitness, nutrition, and youth athletic world, body composition is often used to describe the amount and distribution of body fat (essential and stored fat) and the amount and composition of fat-free or lean mass (muscles, bones, organs—basically everything in your body that isn’t fat).

Compared to BMI alone, body composition has a much more profound influence on athletic performance. Below, we’ve explained 5 ways body composition impacts the health and fitness of young athletes: 

  1. A higher percentage of lean mass means more power. Larger muscles are capable of generating greater amounts of force. Because muscles are responsible for producing the force necessary for movements like running and jumping, a higher level of lean muscle mass in the body contributes to an athlete’s speed, agility, and power. Leaner, muscular legs translate to increased foot speed, for example, while stronger, more muscular shoulders create the ability to throw farther. (Hence why football champ Tom Brady takes care to maintain his level of lean mass).

    Even in sports where athletes benefit from a lower overall body mass—such as long-distance running or cycling—adding muscle can help athletic performance. This is because adding muscle increases power-weight-ratio, or the amount of power that can be produced in relation to body weight. In other words, the power added by increased muscle mass offsets the detriment of additional weight.   

  2. Reduced body fat improves performance. A reduced level of nonessential body fat helps endurance, speed, and agility. Because higher levels of nonessential fat weights down the body, athletes with higher levels of nonessential fat must work harder per given workload. Research has demonstrated increasing body fat by as little as 2 percent of their total body weight may result in a significant decline in sprinting speed and jumping height.

  3. Lean and fat mass distribution influences movement. The distribution of lean and fat mass in an athlete’s body will impact their movement. For example, two offensive linemen of the same weight, height, and body fat percentage will move differently if the majority of their mass is concentrated in their upper body versus their lower body.

  4. Bone density influences injury risk. Low bone density increases risks for stress fractures, poor balance, and decreased overall performance. On the other hand, denser, stronger bones protect internal organs and provide support for muscles while reducing the risk of fractures.

  5. Visceral fat levels impact overall health. For athletes and non-athletes alike, a low level of visceral fat is key to overall health and well-being. Visceral adipose tissue or visceral fat is found around abdominal muscles and vital organs. Compared to the subcutaneous fat that lies beneath the skin, visceral fat is more likely to raise a person’s risk of illnesses and unwanted medical conditions. This dangerous type of fat has been linked to chronic inflammation and several cardiometabolic diseases, including heart disease, diabetes, and Alzheimer’s. 

Why different athletes have different body compositions 

Even among healthy, active young athletes of the same age group, there exists a wide range of different body compositions. Here are the primary factors that play a role in the body composition of young athletes: 

  • Genetics: An athlete’s genes may impact whether they tend to retain fat, in addition to where the fat is stored in the body. 

  • Gender: Females tend to store more body fat in preparation for future pregnancy and nursing. On the other hand, males typically have more muscle mass due to higher amounts of testosterone.

  • Diet: More than any other factor, diet has the most significant impact on an athlete’s body composition. For the most part, this is because consuming more calories than you use causes the body to store the extra energy as fat. Eating a sufficient amount of high-quality proteins can also influence body composition, contributing to higher muscle mass when combined with strength-training. 

In terms of bone composition, a diet that is high in calcium can promote healthy bone density while reducing the risk of fractures. 

  • Preferred sports and training style. Different types of sports and physical activity can also impact body composition. Strength and power athletes involved in explosive exercises—such as football and weight training—may develop more lean muscle mass to provide a stronger muscle contraction while training. Similarly, athletes in anaerobic and aerobic sports—like basketball and soccer—may have lower levels of body fat thanks to a training program designed to improve speed, agility, and endurance. 

As far as bone density goes, athletes who practice strength-training exercises may also develop denser bones. 

The advantages of monitoring the body composition of young athletes with DEXA scanning

There are several ways to perform a body composition scan—including BOD POD testing and hydrostatic weighing—but Dual-Energy X-Ray Absorptiometry (DEXA or DXA) scanning is among the most precise and comprehensive. Here’s a quick summary of what DEXA results include: 

  • Overall body fat percentage.

  • Lean mass balance and fat distribution.

  • VAT estimate, or an estimate of visceral adipose fat tissue (VAT) in the body. The results reveal how much (if any) visceral fat the body has in pounds and cubic inches for volume, in addition to where their risk level currently lies.

  • Bone mineral density.

Routine body composition analysis through DEXA scanning can benefit individuals of all ages and activity levels. Here’s why monitoring body composition of young athletes can be particularly informative for their parents and coaches:

Gain an understanding of an athlete’s overall health and fitness. Merely measuring body mass index does not reveal whether an athlete has the optimal level of fat in their body for their age, sex, and sport of choice. In particular, athletes who strength-train are more likely to have higher amounts of lean mass and therefore higher BMIs than non-athletic subjects, so BMI is often an inaccurate metric when it comes to athletes.  

By comparison, body composition is a clearer indicator of an athlete’s current health and fitness level. By revealing their percentage of body fat, body composition results reveal whether an athlete is at greater risk for developing health complications. From a fitness standpoint, an athlete with excess body fat may experience impaired athletic performance because of the reduced power-to-weight ratio. 

Pick up on asymmetries. DEXA scanning can catch muscle asymmetries between an athlete’s left and right sides. Muscle imbalances may develop in young athletes when a sport causes them to favor one side or when improper form overworks a dominant side. These asymmetries can throw off weight distribution, further muscle imbalance, and result in stresses that lead to injury. Picking up on these asymmetries through DEXA scanning enables the athlete to make adjustments to their training and form to correct them. 

Injury prevention. As they recover from an injury, an athlete may lose muscle tissue around the area that is rendered temporarily immobile. As a baseline, a pre-injury DEXA scan can be compared to a post-injury DEXA scan to make sure lean mass returns to pre-injury levels. Ensuring their lean muscle mass returns and remains stable is key to preventing re-injury. 

Assess the effectiveness of training and nutrition programs. Monitoring body composition over time can help athletes and coaches see how training and nutritional changes are impacting the body. The effects of training and nutrition may be observed via changes in lean muscle and fat in the body. Routine DEXA scanning can reveal whether a fitness and nutrition plan is working as intended, and confirm that any weight loss is stemming from a decrease in body fat as opposed to lean mass. Having accurate, quantifiable data on the effectiveness of a training and nutrition program during different times of the season can help coaches and nutritionists develop custom programs tailored to an athlete’s unique needs. 

Catch sudden changes in body composition. Particularly among at-risk athletes with low body fat, sudden changes in body composition may indicate health problems. For example, female athletes who have very low BMIs (18 and below) may be at risk of developing female athlete triad, a relatively common condition among young female athletes involving a combination of disordered eating, amenorrhea (menstrual dysfunction), and low bone mineral density. 

It should be stressed that particularly when dealing with young athletes, body composition measurements are shared with caution and great sensitivity. While highlighting the positive impact of a healthy lifestyle can help improve self-image, focusing on minor weight gain or comparing body composition to other athletes can harm body image and lead to eating disorders.

Improve self-image. When shared sensitively, body composition results can be used to improve a young athlete’s self-image. Traditional measures like mirror appearance, scale weight, and BMI can be discouraging and misleading. Body composition results, on the other hand, show that the body is complex and provide a more accurate picture of how an athlete’s body is responding to their hard work on the field.

By using DEXA scan results to inform training programs and provide positive reinforcement, parents and coaches can help young athletes avoid injury, prevent disease, and improve their overall health and performance. To schedule an assessment, look up a DEXA scan near you.  

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