Chapter 13 - Body Composition Flashcards
body composition and athletic performance
While various aspects of an athlete’s physique play an important role in determining performance, body mass and composition are often seen as focal points given their ability to be manipulated through training and diet
dynamics of energy balance and body composition
facilitating fat loss
To facilitate reductions in total body fat, an energy deficit is required, whereby total daily energy expenditure must exceed total daily energy intake
While additional exercise is a primary factor in increasing energy expenditure, manipulating energy intake provides a greater opportunity to impact body composition, especially in individuals who are already undertaking high training loads. Although reducing energy intake between 250 and 500 kcal per day is the typical recommended starting point, customized prescription should be based on the individual athlete’s specific requirements, agreed-upon timescales, and constant fine-tuning based on the available measurement tools to assess progress
challenges in altering body fat %
as athletes lose weight, their energy requirements also change. They will typically require fewer calories to maintain their new body weight
what do nutrition strategies targeting loss of fat mass do?
aim to
1. minimize any detrimental effects on performance
2. simultaneously preserve muscle mass.
Nutritional Strategies to Support Reductions in Fat Mass
Avoiding Severe Energy Restriction
To achieve quick weight loss results, athletes are commonly tempted to severely restrict energy intake as opposed to following a slower, sustained approach. However, dramatic reductions in total energy intake can quickly lead to the loss of muscle mass and should be avoided
it has been previously demonstrated that when energy intake is reduced by 40% over a period of 30 days, 58% of total weight lost came from fat-free mass, equating to 1.9 kg (4.1 lbs)
Nutritional Strategies to Support Reductions in Fat Mass
Monitor protein intake
During periods of energy restriction, protein intake plays an important role in preventing the loss of muscle mass
For instance, it has been previously reported that during periods of severe energy restriction (60% of habitual energy intake), increasing dietary protein from 1 g/kg BM to 2.3 g/kg BM, minimized the loss of lean mass by over 1 kg
Furthermore, Longland and colleagues (2016) recently showed that in some instances, higher proteins diets of 2.4 g/kg BM may allow for muscle mass gain during periods of energy deficit. In this study, despite a 40% reduction in energy intake, subjects in the high-protein group increased lean body mass by an average of 1 kg compared with those who consumed a lower protein diet
Nutritional Strategies to Support Reductions in Fat Mass
nutrient timing
Nutrient timing plays an important role in ensuring sufficient energy is available to support training and recovery while still ensuring that the required energy deficit is maintained. In this regard, it seems logical to ensure that sufficient energy is consumed both before and after key training sessions to maintain the desired training quality and to promote the replenishment of muscle and liver glycogen in the immediate recovery period
However, at times when performance is less of a priority, restricting energy intake to a small feeding window may help the athlete to reduce overall energy intake across the day, as covered in Chapter 12.
Nutritional Strategies to Support Reductions in Fat Mass
Low-Energy-Dense Food Choices
these diets are often lower in fat and higher in fiber, which allows for the consumption of large amounts of volume for an overall lower energy intake to improve feelings of fullness.
effectiveness has been clearly demonstrated in multiple well-controlled laboratory feeding studies as well as within free-living conditions
When eating in an energy deficit, how much protein (g/kg body mass) has been shown to help maintain muscle gain?
2.4g/kg
body composition models
2 component model
fat mass and fat-free mass
Body mass = fat-free mass + fat mass
One limitation of this model, however, is that it is unable to distinguish between water, protein, glycogen, and minerals in bone and soft tissue. In other words, fat-free mass includes muscles, organs, bones, water, and even teeth.
body composition models
3 component model
fat mass, water, and fat-free dry mass
Body mass = total body water + fat-free dry mass + fat mass
body composition models
4 component model
- fat mass
- protein
- water
- mineral
Body mass = total body water + bone mineral + fat mass + protein
Methods for Body Composition Assessment
skinfold assessment
- most frequently used technique to assess body composition in a sporting environment is measuring skinfold thickness using a caliper instrument
- represents an example of a two-component model, where total body mass is split into fat mass and fat-free mass
- These measurements allow for the assessment of fat located underneath the skin, known as subcutaneous fat, which can be used to estimate total body fat
what are the locations for the skindfold assessment?
8 total
- biceps
- tricpes
- subscapularis
- iliac crest
- supraspinal
- abdominals
- front thigh
- medial calf
how to execute a skinfold assessment
- the skinfold should be held between the thumb and forefinger and measured within 2 seconds to avoid compression of the site
- complete measurements twice and taking an average of the two values to improve the reliability and validity of the measures. If there is considerable (> 10%) variation between the two measures, then a third measure is required
- sum the average thicknesses from each of the measurement sites and enter those into an online calculator
Methods for Body Composition Assessment
bioelectrical impedance analysis
- most frequently used technique to assess body composition in a sporting environment is measuring skinfold thickness using a caliper instrument
- represents an example of a two-component model, where total body mass is split into fat mass and fat-free mass
- These measurements allow for the assessment of fat located underneath the skin, known as subcutaneous fat, which can be used to estimate total body fat
how does bioelectrical impedance analysis work?
- Resistance is measured through the contact of electrode surfaces to different body parts, typically the hands and feet
- A weak electrical current is applied to one of these electrodes and measured at the other
- The lower the measured resistance, the higher the total body water content, thus indicating lower amounts of fat mass. In other words, the faster the electrical current flows through a person’s body, the lower the body fat percentage. Based on these differences in resistance, BIA can be used to estimate an individual’s percentage of body fat, fat-free mass, and total body water (Figure: Bioelectrical Impedance)
what are some limitations to bioelectrical impedance testing?
hydration status and fluid distribution between tissues affect the data’s validity
For example, the loss of water through prior exercise or voluntary fluid restriction will result in the overestimation of total fat content, while hyperhydration will lead to an underestimation of body fat content. This highlights the need for standardized best-practice procedures prior to assessment.
Methods for Body Composition Assessment
Dual-Energy X-Ray Absorptiometry (DEXA)
- measures body composition by passing low energy X-ray beams through the individual being assessed and recording the loss of signal in various parts of the body
- To distinguish between soft tissue and bone, as well as between fat and fat-free mass, this measurement is performed at two different intensities and can be completed in as little as five minutes
2-3% error
Methods for Body Composition Assessment
Ultrasound
use high-frequency sound waves that pass through the surface of the skin into the underlying tissues. Once these waves come in contact with a tissue’s surface, it is partly reflected back to the probe as an echo. These echoes are subsequently converted into signals for processing, with the strength of each signal being represented by a dot
requires a highly skilled technician for correct application
Like all other assessment methods, exact estimations are difficult/impossible
Methods for Body Composition Assessment
Air Displacement Plethysmography
follows a similar approach to underwater weighing by measuring total body volume, but it is performed in a sealed air capsule as opposed to under water. Air displacement plethysmography offers a more user-friendly experience compared with underwater weighing and is able to provide rapid measurement in under five minutes.
how to conduct Air Displacement Plethysmography
- collection of body mass
- enter the chamber (usually wearing a swim cap and swimwear), and total body volume is measured by subtracting the air that has been displaced with the individual inside from the original volume in the chamber
- the individual breaths into an air circuit to assess pulmonary gas volume which is then subtracted from total body volume to provide a true representation of actual body volume
- Body density can be subsequently calculated from body mass and body volume and converted to provide an overall estimation of body fat.
generally underestimates body fat % when compared to other methods
Factors that Influence Body Composition Measurement
4 total
- shifts in hydration status
- gut content
- prior exercise
- intramuscular substrates such as glycogen and creatine
what are fundamental prerequisites to successful body fat % testing?
includ:
1. performing tests in a fasted state
2. ensuring that no exercise is completed 12–24 hours prior to each assessment
3. standardizing hydration status between measurements
BMI for athletes
Metric Formula: BMI = body mass (kg) / height (m)2
Imperial Formula: BMI = 703 × weight (lb) ÷ [height (in.)]
given the inability of BMI to distinguish between the various components of body mass (e.g., fat mass, fat-free mass, water), individuals with distinct differences in body composition may present with the same BMI
Identify Physique Characteristics for Each Athlete
Initial body composition assessments should be used to determine whether specific training or nutritional interventions are required to provide a performance or health benefit to the athlete
To do this, an understanding of the performance determinants of the athlete’s sport is required
each sport will have different body composition requirements, even between various playing positions within the same sport. Nonetheless, various normative data sets are now available to help practitioners provide an optimal body composition target range for athletes across multiple sports. This data is typically presented as either a sum of skinfolds or can be derived from DEXA scans. Thus, when using such data as a comparative tool to inform decision making, it is essential to consider the assessment method, the standardized assessment protocol, and which skinfold for skinfold measurements.
Monitor the Effectiveness of Training and Nutrition Programs
Monitoring changes in body composition is necessary to determine the success of any training and/or nutrition intervention. When each athlete is monitored continuously throughout the intervention (as opposed to simply before and after), this data allows for constant fine-tuning of the strategy based on individual responses
Determine Safe and Achievable Body Composition
Body composition estimates provide an important tool for prescribing realistic and safe weight-loss targets for athletes. Such practices are important because some athletes, especially those in weight-category sports, will commonly attempt to fight in categories that are unachievable to try to gain the biggest competitive advantage. For example, a super-middleweight boxer who weighs 75 kg (165 lbs) with a body fat of 7% may not be able to reach a light-middleweight cutoff of 69.85 kg (154 lbs) through the loss of body fat alone, given a total body fat mass of 5.25 kg. As such, fighting in this category should be advised against or, alternatively, may require a reduction in lean mass over time
what factors should be considered when deciding an apropriate body fat % for an athlete?
- genetics, age
- history of weight-cutting and weight regain
- duration to achieve weight loss
normative body fat data
normative body composition data from DEXA
To avoid severe energy restriction and support maintenance of fat-free mass and performance, what percentage of body weight loss is recommended weekly?
0.5 - 1% weekly
