How BMI Impacts Sports and How Much You Should Depend on It

Does BMI impact your sport? Chances are it does. Strength is related to muscle size and a lean body mass helps you generate more force in a specific amount of time. Lean body mass contributes to quickness, speed, agility, and performance. By reducing non-essential body fat, you can potentially enhance muscular and cardiorespiratory endurance. On the other hand, additional body fat can inhibit balance, coordination, movement, and endurance making it detrimental to your overall performance.

Endurance athletes, such as runners, benefit from low body fat and lower BMI. Basketball and football players need quickness, speed, strength, and agility so they need low body fat while increasing lean muscle mass. Tennis players need flexibility, strong wrists, and agility, which also means low body fat.

While BMI is not an exact indicator, as we will see in a bit, it does play a part in different positions when it comes to various sports.
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BMI Considerations Based on Sports

When you look at professional athletes and compare a rugby player to a runner, chances are you are going to notice a big difference. The reason is that their bodies have different needs for varying sports. We’ll go through the sports and see what each body demands for the best performance.

Overview of Elite Athlete's BMI

Runners

When looking at the body makeup of runners, we look at long-distance runners versus sprinters. Long-distance runners have leaner muscles, which is especially true when it comes to the lower body.

Long-distance runners need to focus on more aerobic training where sprinters need larger muscles on the thighs and calves for powerful bursts of energy. Leaner athletes’ bodies are more efficient at delivering oxygen through the body so they can dissipate heat better and burn carbs more efficiently.

When you run a marathon, you don’t want bulky muscles weighing you down. If a sprinter ran a long distance with the weight and bulk of muscles they normally have their time would be severely slowed because of the extra bulk. Furthermore, running long distances tend to constantly burn calories which is another reason long-distance runners are leaner.

However, if runners’ BMI gets too low their health will suffer and experienced weakened immune systems and/or weakened bones. The American Exercise Council on Exercise recommends a BMI at or above 18.5 and body fat of 14 percent for women and six percent for men.

The best athletes in sprint events tend to have a larger mean mass and height than long-distance runners. This is because sprinters need more muscle mass to hit the ground to create a powerful energy. The start, reaction time, and acceleration phase are crucial so smaller runners have better reaction time and shorter legs have a lower moment of inertia so it takes less energy to accelerate.

Elite Long Distance Runners Compared to Everyday Marathon Runners

Paula Radcliffe has a BMI of 17.3 at 45 years of age. She started running at the age of seven but started taking the sport seriously when she was 12. Her first national race was at that age and she placed 299th out of 600. A year later, when she was 13, she placed fourth in that same race.

Tirunesh Dibaba is 28 years old and has a BMI of 18.4, just under what is considered normal. She started doing athletics at the age of 14. Her first international event was when she was 15 years old and she placed 5th.

At 26 years old, Dafne Shippers has a BMI of 28 putting her in the overweight category. She started competing as a sprinter at the age of nine. In 2010, at the age of 18, she won two gold medals in Junior Championships Athletics.

So how do these stats compare to the average female runner’s BMI?

In females aged 32 to 47 — who had run an average of nine years — they had an average BMI of 21.4 coming in the normal range. Younger runners, ages 16 to 31, who run an average of eight years had similar average BMIs of 21.9. For more experienced runners who had run an average of 10 years — ages 48 to 63 — they came in with an average BMI of 21, which is the lowest of all the groups.

This somewhat corresponds to the above elite runners. The elite runners have trained longer, which explains their lower BMI. By following the trend of lower BMI for more years of training, we can assume the trend would be that BMI would keep lowering.

Sprinters Compared to Elite Athletes

Competitive sprint athletes body size corresponds with elite sprinters in a study that showed they had relatively high body mass. In the study, 15 of the 98 competitive male sprinters studied were classified as overweight. The remaining sprinters were in the upper normal range for BMI.

So What is the Ideal Running Weight?

While body makeups differ between runners, everyone has an ideal racing weight. Running above your ideal weight can increase your time by two seconds per mile for every pound above your ideal racing weight. For example, if you are 10 pounds over your ideal racing weight then you could potentially shave 20 seconds off your time by losing those 10 extra pounds. Plug your numbers in the chart below to find your ideal running weight.

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The important thing to remember about your racing weight is that your body needs enough fuel to perform, so it is more of a guideline than a hard set rule.

BMI of Elite Athletes in Other Sports

Baseball

Since 1991, the average BMI of baseball players has been on the rise. Over the last 25 years, about 80 percent of players fell into the overweight or obese category when it comes to BMI. According to the linked study, the rise of BMI coincides with the steroid era along with advances in sports science. However, more force means more power so the ball will travel further.

So what does the ideal baseball player look like?

Baseball is one of the few sports where the players come in all shapes and sizes. The average baseball player is 207 pounds and stands 6’2”, but the body shapes vary from tall and thin, tall and heavy, too short and thin and short and heavy.

Baseball Player Height

Different positions require different body types. Pitchers tend to be taller and average weight where catchers tend to be the opposite (shorter and heavier). The first baseman tends to be taller where a second baseman tends to be shorter and lighter.

How do American Footballers Compare?

American football players tend to be above average in weight and BMI. Linemen are the strongest and largest body size because the mass provides them with the inertia they need so they can play their position with greater stability.

American Football BMI

So why such a wide range of different BMI within the same sport? Running backs and linebackers need speed and agility. Wide receivers and defensive backs need to be fast and have good coordination. The quarterback, kicker, and punter need a good arm, excellent footwork, speed, and strength.

The tight end position normally has taller men where running backs tend to be shorter and quicker. Tight ends also have lean mass in the upper body and greater mass than linebackers and running backs.

Offensive linemen are taller and heavier than defensive linemen, but they tend to have similar lean mass and distribution of that mass. Wide receivers are taller and heavier than defensive backs, but they have similar body fat percentage, fat mass, and lean mass.

Football

Football coaches tend to look for tall, lean players. The top six teams in England were taller and leaner than the less successful teams in the league. Having a tall, lean body means it is easier to run, jog, or spring the five to seven miles required in a match.

A college study showed that goalkeepers were the heaviest and tallest where midfielders were the lightest and shortest. Central defenders were the tallest and heaviest when compared to external defenders. So what does the average footballer look like?

The International Centre for Sports Studies in Switzerland compiled data that showed the average height of a footballer is about 5 ’11 1⁄2″.

Rugby

CNN recently completed a study that found the height of New Zealand backs increased by four inches and their weight increased by 31 pounds over a 10 year time period. This makes sense when it comes to rugby because bigger tends to be better.

We know the mean height of the population is rising, but the advancing knowledge, training, and conditioning athletes also explains these changes. Rugby players are now stronger, faster, and bigger than they were before.

So how do they keep the weight on? Professional rugby players eat anywhere from 220 to 300 grams of protein a day. Keep in mind the average male consumes 55 grams of protein a day.

New Zealand wasn’t the only ones to see an increase in weight, England did as well. The average England rugby player in 1994 weighed 92.3kg and in 2014 weighed in around 105.1kg. The increase and average runs about the same as New Zealand as their average weight in 1985 was 90kg and was 104kg in 2014.

However, bigger players mean bigger hits, which also increases the risk of concussions. Over the last 10 years, concussion rates have increased 400 percent in rugby.

Each position has a unique body type. Backs are large and fast and offer speed and agility to the team. Forwards use strength to get the ball so they tend to be the heavier players on the team. The following is a chart of height, weight, and lean muscle distribution among positions:

Rugby Positions

Tennis

Tennis has also seen an increase in height over the years. The average height of the male tennis player over 50 years was seven centimeters where the average female height increased by 10cm.

General strength and flexibility are needed to prevent injury. The player needs short, repeated bursts of energy during the match along with being able to move in a multidirectional fashion fast. A firm wrist and solid shoulder help when it comes to serving.

A study showed that fatigue affects the sensation of joint movement, decreases athletic performance, and increases fatigue related shoulder dysfunction. In fact, when a player is nearing volitional fatigue hitting accuracy can be reduced up to 81 percent with the serve being the most obvious stroke to deteriorate.

A study on agility was performed and showed that BMI correlated to the 505 Agility Test. BMI increased power output but agility performance decreased in collegiate players.

Ice Hockey

Elite ice hockey players train to focus on muscle strength, anaerobic power, aerobic capacity, agility, speed, and overall power. A negative correlation between skating speed and fat mass has been shown over the years.

Elite hockey players have an average body height of 184.3cm, which corresponds with the NHL whose players have an average height of 182 to 187cm. The BMI of top performers ranged from 25.5 to 27.15.

The ideal ice hockey player has long arms and a heavy torso, the latter being much more important for goalies. Furthermore, players tend to have shorter legs with smaller calves.

Boxing

Heavyweight boxers are at their best when they have a lower body fat percentage. Yet, body fat that is below five percent can be dangerous. The average healthy male should have around 20 percent body fat. Between eight to 10 percent body fat is ideal for male boxers and 12 to 14 percent for females. The muscle mass is needed to speed and to take hits and extra fat limits speed and movements.

Is BMI the Best Measurement?

As seen from above, BMI in elite athletes can range from overweight to underweight and everything in between. So it is really the best measurement? Especially when it comes to athletes?

The shortfalls of a catchall BMI is the measurement doesn’t take into account fat, muscle, characteristics of bone, body composition, and body shape. However, that doesn’t mean you should completely ignore it.

BMI measurement can be a good guide, but keep in mind that it doesn’t take into account your body shape and fitness level.

Why Do We Even Have BMI?

BMI is used as a prevention or a risk assessment, but it is not a diagnostic tool. That means if you are a sprinter and fall into the overweight category, chances are you are healthy and fit even though you have a higher BMI.

BMI is commonly used by doctors to screen for health problems stemming from weight issues. For example, a higher BMI can mean increased risk for:

  • Cardiovascular disease
  • High blood pressure
  • Gallbladder disease
  • Type 2 diabetes
  • Osteoarthritis
  • Certain types of cancer
  • Mental health disorders

Once a doctor determines a person is overweight or obese through the use of BMI they then perform further tests.

Best Way to Determine Body Fat

There are plenty of other ways to determine body fatness that do not include BMI, however, they are more time consuming and can be expensive. If you want the most accurate determination, the following are the best ways:

  • Skinfold Thickness Measurements
  • Underwater Weighing
  • Bioelectrical Impedance
  • Dual-energy X-ray Absorptiometry (DXA)
  • Isotope Dilution

Skinfold Measurement

Skinfold measurement is also called caliper testing. It is so accurate it predicts body fat within three to five percent of underwater weighing. So how does it work? You will need a pair of calipers before you start.

Grasp the fold of skin between your index finger and thumb — this should include the thickness of skin and subcutaneous fat but not include the muscle. Put the calipers at a 90-degree angle and hold. Read the need to the nearest 0.1mm.

Take all the measurements on the right side of the body in a rotational order. Always use your index and thumb of your left hand. Complete a minimum of two measurements at each site. This should not be done after exercising or if you are wet as you may not get accurate results.

The Dumin & Womersley Four Site Test is the most commonly used when it comes to skinfold measurement. Complete measurements at the following areas:

  • Tricep Skinfold
  • Bicep Skinfold
  • Scapula Skinfold
  • Suprailiac Skinfold

Underwater Weighing

Underwater weighing measures total body density and is the gold standard for body composition assessment. It determines the percentage of body fat extremely accurately.

Once you find a university or clinic that has underwater weighing equipment, you can expect the following:

  • Weighed on dry land
  • Get into a tank of water while sitting on a special scale
  • Lowered into the water and exhale air out of lungs
  • Stay still
  • Complete three times for an average

Bioelectrical Impedance

Bioelectrical impedance measures body fat in relation to body mass through electrical impulses. Don’t worry, they are not painful. Electrodes are placed on the right hand and foot and the flow of the current is affected by water in the body. The device measures how that electrical signal is impeded through different tissues. For example, fat and bone slow down the signal where blood and fluids have higher conductivity. After measurements are taken, an equation that takes into account age, gender, height, and weight is used to calculate body fat percentage.

DXA

DXA or a bone density scan uses x-rays to determine your total body composition. The scan provides details such as how bodyweight breaks down into bone, tissue, and fat. This is also highly accurate and can track changes over time. The scan takes about three to 12 minutes to complete.

Isotope Dilution

Isotope dilution assesses body composition at a molecular level using urine samples. First, the technician will take a baseline urine sample and you are weighed in minimal clothing. Deuterium oxide is then given to drink because it mixes with water in the body. Over the next one to 14 days, you will provide urine samples. These samples are then measured using Isotope Ratio Mass Spectrometry.

Conclusion

While BMI can be used as a guideline, it should not be followed as a hard and fast rule. There are many measurement types that provide a more accurate reading and the caliper test can even be done at home. No matter what your BMI is, make sure you are healthy and have enough energy to perform your sport of choice.

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