Fitness Corner: Body Fat

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In this latest Fitness Corner, Johnny Parker and Duane Carlisle join the 49ers team nutrionist in discussing body fat and body fat measurement.**

Body fat percentage is a useful tool for measuring the physical progress of an athlete. Strength and Conditioning coaches Johnny Parker and Duane Carlisle analyze their players before and during the season in order to ensure that a player is in peak football shape.

"We test guys during the offseason, at the beginning of the offseason and again at the end," Carlisle said. "We test them on an individual basis during the season. If we are monitoring a player's weight, we would also look at their body fat and ask them to come in and be tested."

The results of the test can vary slightly depending on the type of test used.

"The only way to truly accurately measure body fat is when the person is dead," Parker said. "You cut off body parts and do an analysis."

Thankfully, the 49ers don't have to resort to this method of measurement. There are a host of other methods at their disposal. Team nutritionist, Dr. Suzanne Nelson, assists with much of the measuring and testifies to the vast array of measurement possibilities.

"You can do measurements with x-rays, circumferences, skin folds, under-water weighing, and BOD PODS," she said.

The latter method, a BOD POD, is the accepted norm by the NFL. Just like its name would suggest, a player puts his body into the pod and a measurement is then calculated.

"You determine total body density by a measure of volume displacement," said Nelson. "If you know that density is equal to mass divided by volume, you weigh the individual on a scale so you know their mass. Then you calibrate the machine and it's a known volume inside the machine. Then you put the individual in there and whatever volume they displace with their body, you subtract from the known volume of the chamber so then you have the player's volume. So if you have the mass and the volume, you can then determine body density. Then through a conversion equation, you can then determine body fat."

While it may seem like a complicated formula, the results are as accurate as possible without having to wait to take a posthumous measurement.

"It's got good track-ability," Nelson said of the BOD POD. "It's comparable to under-water weighing. That's based on Archimedes principle of water displacement and this is air displacement."

Under-water weighing does have one significant drawback however, making the BOD POD the most reliable and consistent method of measurement.

"If the subject is afraid of the water, they won't be able to expel all the air out of their lungs and you won't be able to get an accurate reading there either," Parker said.

The simpler and most widely used device outside of the NFL is a skin-fold caliper. You squeeze the calipers on a person's skin in various places on their body. The calipers measure the amount of skin that is squeezed between the calipers. Those measurements are then added up in order to give a complete measurement.

There are set ranges for body fat based on the position of the player, which are targets for the athletes, but Coach Parker noted that some body fat does serve a purpose.

"You don't want to get too lean," Parker said. "Fat also serves as a cushion for your organs, bones and joints. You don't want to eliminate all fat, but leaner is always better."

It is important to note that while offensive and defensive linemen may be allowed a higher percentage of body fat, the goal is never to have a player increase fat.

"There is something to be said about when they're on the line and they're pushing," Nelson said. "If they're bigger and they're harder to move out of the way, you might think 'Well let's just bulk them up.' For an athlete, fat is considered dead weight. It's just going to slow them down."

By ensuring that the players all have their body fat percentage in a healthy, athletic range, it is hoped that they will not only perform well on-the field, but stay healthy long after their careers have ended.

"Excess body fat is related to heart disease and certain cancers," Nelson said. "You definitely are focusing for their sport as well as longevity in their health. After they're done in the league, we want them to go on and lead healthy lives and minimize injury."

Questions from the readers:

Chuck writes: I just finished reading your column on the 49ers site about hip flexor injuries. I sustained a hip flexor injury (I think) playing tennis over 3 months ago and have been unable to overcome the injury. I'd appreciate any additional information you might share with me. Thank you for taking a couple minutes to think about this.

Parker's response: First of all, we are very appreciative of all of our fans, but it would be very dangerous to give anything relating to medical advice to you until we learn about your age, injury history, level of fitness and more particulars about that. We would be doing you a disservice to even think about making that type of recommendation. That's a medical question. If you are  concerned about that, you should see a physical therapist and ask them what you can do to help that problem. We would be ill-serving our fans to give any sort of medical advice. We're not qualified to do that. We're not medical people. We try to prevent medical problems.

Anthony asks: I am overweight and have been my whole life from grade school to high school. I need some advice on an exercise/eating program. I weight about 290, but I am built also I just want to be around to see my kids grow up. I am also scared about being a diabetic later in life since it does run in the family. If at all possible any advice would work.

Parker's answer: That's really a life issue and not an exercise or diet issue. I have some personal experience with diabetes and know that you have got to get his weight down and probably a lot. Any matter of weight loss in the simplest terms is burning more calories than you ingest. I hope that you are aware of the specific dietary needs of a diabetic and that you obeys those to the letter. Diabetes is an uncaring enemy. It has no sympathy and no mercy. You've got to make sure your blood sugar is down. That's a serious thing.

To have your fitness related question considered, please email Carlisle and/or  Parker at fitnesscorner@niners.nfl.com

Coach Carlisle also has training videos available. Find out more by visiting his own website by clicking here! 

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