Body composition
Body composition describes the distribution of lean body mass and
body fat mass.
Fat mass refers to the percentage of body weight that is stored
fat.
Lean body mass is the weight of the rest of the body – muscle,
bone, connective tissue, and organs.
The average male has 12-18% body fat, with the average female
being 22-28% body fat.
Typical values for elite athletes are 6-12% for males, and 12-20%
for females.
This figure will vary depending on the sport.
Size and body composition in relation to sport
The ideal size of an athlete will depend on the sport or event or the
position played within the sport.
Whilst body size and build are important for certain sports, body
composition is still important. For example, a basketball player needs
to be tall, but if they have a high percentage of body fat this will
adversely affect their performance. The extra weight, made up
from fat will act to slow them down.
Standard ideal height and weight charts, such as BMI do not work
for athletes. They do not account for body composition. Athletes
typically have a higher proportion of muscle, which weighs three
times as much as fat. This makes them much heavier for their height
than the average person. A BMI chart would likely measure them as
being obese, despite them possibly having a very low percentage
body fat.
When measuring body composition we tend to focus on body fat as
opposed to lean body mass. In most sports it is advantageous to have
a lower percentage of body fat, so most athletes try to minimise
their body fat.
Body composition assessments/tests
Body Mass Index (BMI)
BMI measures an adult’s weight in relation to their height.
Their weight is divided by their height in metres squared.
weight (kg
BMI =
__________________
height (m) x height (m)
e.g. A person who weighs 75kg and is 1.80m tall
75 divided by (1.8 x 1.8)
75 divided by 3.24 = 23
Acceptable range for a male is: 20.1 – 25
For a female: 18.5 – 23.8
So this individual would be within the acceptable range.
Now check your BMI! How do you score? Don’t worry, you’re an
athlete with a greater percentage of muscle mass!!
25- overweight
30 – obese
Know these figures – normal, overweight, obese!
- BMI does not directly measure body fat.
- A little better than standard height/weight tables.
- Not suitable for young children, pregnant women, the elderly,
or athletes.
- Athletes higher proportion of muscle pushes them outside the
normal range, despite their body fat being well within normal
the range.
- BMI is the medical standard used as part of the government’s
objectives to slow down the trend of increasing obesity within
the UK (despite its failings).
Hydrostatic weighing
Athlete is weighed totally immersed in water.
The difference between the athletes ‘dry’ weight and the
underwater weight indicates the athlete’s fat percentage.
Fat floats – so the greater the body fat, the bigger the difference
between the two weights.
Advantages
Most accepted and accurate measure of body composition.
Disadvantages
Only an estimate of the density of fat-free mass- this varies from
gender, age and race ( not totally accurate).
Not readily available to most people.
Bioelectrical Impedance Spectroscopy
BIS scales send a safe, low electrical current through the body.
The current flows easily through the fluids contained within muscle
tissue but encounters resistance when encountering fat. The fat
impedes (to help you remember the name) the flow of the current.
Having programmed in the athletes height and weight, the scales
work out the body fat percentage.
Advantages
Reasonably accurate.
Disadvantages
Affected by the hydration level of the performer (as it relies on the
fluid levels of the fat-free tissue such as muscle).
Uses average population fat-free tissue values to work out fat
percentage– so not suitable for athletes.
A number of factors can affect the accuracy of the test: Eating
habits/alcohol consumption/exercise/time of day.
Skinfold measurements (callipers)
Skinfold callipers measures (in mm) subcutaneous fat (below the
skin) from a number of sites on the body.
The sum of the measurements is used to estimate body fat
percentage.
A number of tests are available, using different parts of the body.
The most popular test measures biceps, triceps, subscapular,
suprailiac.
More detailed tests more sites on the body, or are gender specific.
Advantages
Most widely used method of assessment. Accessible, cheap and
practical to use.
Provide a good estimate of body fat percentage (multiple
site/gender specific tests)
Disadvantages
Testers need training, to ensure the specific sites are measured
accurately.
The energy balance
Two parts to the energy balance:
Energy intake – food
Energy expenditure – work/physical activity
If energy intake exceeds energy expenditure the excess is stored
as fat.
If energy expenditure exceeds energy intake weight will be lost in
the form of fat.
High levels of body fat which classifies the individual as overweight
(over 25 BMI) or obese (over 30 BMI) comes as a result of energy
intake exceeding energy expenditure.
Remember that the BMI score is not the body fat percentage.
Obesity – body fat percentage
male – 20-25%
female – 30-35%
Energy expenditure and intake
Energy expenditure
There are two parts to energy expenditure:
Basal Metabolic Rate (BMR)
Metabolic rate is the rate of the body’s energy expenditure.
Basal metabolic rate is the lowest rate of energy expenditure to
sustain the body’s essential physiological functions at rest. In other
words the energy we would use sitting down, doing nothing, except
allowing the body systems to function.
Sometimes the term Resting Metabolic Rate (RMR) is used – this
takes away the need to measure sleep.
The term Thermic effect is used to describe the energy used in
eating, digesting, absorbing and using food (approx. 0-20%)
You can calculate your RMR:
Males – multiply body weight (in lbs) by 10. Add double the body
weight to this value. E.g. 150 lbs: 150 x 10 = 1500 +(150+150)
1500 +300 = 1800 cal/day.
You can divide this total by 24 to work out the hourly RMR
1800 divided by 24 = 75 cal/hour.
Females – multiply the body weight by 10. Add the body weight to
this value. E.g. 150 lbs X 10 =1500 + 150 = 1650 met/day or
1650 divided by 24 = 69 cal/hour.
Try working your own RMR.
This figure will be the calories that you need to consume to sustain
your body’s energy requirements at rest.
Activity energy measurement (METS)
METs stand for Metabolic Equivalent Task.
METs are the ratio of the activities working metabolic rate relative
to the resting metabolic rate.
For example the resting metabolic rate is given a value of 1.
Slow walking on the flat would have a value of 2 METs.
This suggests that your energy expenditure would double.
Compare this to running at 6mph(10 min miles) has a value of 10
METs.
See the full table of activities and their METs in the textbook on
p470-471.
By calculating the energy requirements/expenditure you can work
out the calorific intake (energy intake) that is required to either
sustain weight or lose weight.
This is also important for an athlete to ensure that they are taking
in enough calories to provide enough energy for their physical
activity.
If expenditure is greater than intake – weight (fat) will be lost.
If intake is greater than expenditure – weight will increase in the
form of stored fat.
This knowledge is important for those who are overweight or obese
and are managing their weight.
Note - be aware that this section is relevant from a sporting and
health context.
Energy Intake
Energy intake is the food that we eat.
The UK department of health gives a recommendation of
average daily calorific requirements:
Males – 2550 cal
Females – 1940 cal
However the actual value for an individual will vary
depending on age, height, weight, activity, lifestyle and body
composition.
A balanced diet.
10-15% protein
No more than 30% fat
55-60% carbohydrates
Also should include:
Vitamins, minerals, roughage and water.
Performers involved in high volume training, particularly endurance
training will require a higher percentage of carbs (15-20% more).
Such athletes could require 5000-6000 Kcal/day to balance with
their energy expenditure.
Health implications of being overweight/obese
- Increased risk of diabetes (particularly type 2).
- Increased risk of cancers.
- Increased risk of heart disease, deep vein thrombosis (DVT),
stroke (resulting from long term stress on the CV system).
- Overloading joints impacting on posture and alignment – leads
to musculo-skeletal pain.
- Psychological harm of stigma, bullying and low self esteem.
- Low self esteem leading to social difficulties.
- Under performance in physical and mental work.
Implications for involvement in sport
- Overweight/obese performers will have an increased energy
expenditure for a given activity than those whom are not.
- There is a greater load on the joints and risk of injury
(through greater wear and tear or acute force trauma).
- Decrease in joint mobility/flexibility.
- Decrease in economy of movement.
- Decrease in fatigue resistance.
- Negative cycle – overweight/obese individuals have a negative
view of physical activity.
- They are unlikely to take part due to the associated stigma of
being overweight/obese - worry about how they are perceived
by others.
Effects of physical activity on body composition
Performance implications of body weight
- Low body fat is a characteristic of successful performers.
- Athlete’s weight is often relatively high due to high proportion
of muscle.
- Anaerobic athletes tend to be heavier, aerobic athletes less so
due to the difference in muscle mass.
- Low body fat is most significant in aerobic activity, as any
weight that is not used in metabolism (energy) or movement
(muscle) is carried for longer, wasting energy. This wasted
energy could be used for increasing performance.
- Excess fat reduces the power to weight ratio. This will effect
speed of movement/acceleration.
- Increased weight from muscle mass is fine if it adds
power/force to the specific movements involved in the sport.
- Very low body fat can also have an impact on health. This can
be the case for some athletes who are involved in high volume
training and low body fat is advantageous.
- Body fat below 5% in males and 10-15% in women can have a
detrimental effect on the immune system, increasing the risk
of illness.
- Female athletes are at greater risk of irregular menstrual
cycles below 18% body fat.
- Females with a low fat mass have a decreased oestrogen levels.
This increases the risk o osteoporosis, a decrease in
density/weakening of the bones (remember from last year’s
work).
Effect of physical activity on body composition
- Increasing physical activity increases calorific expenditure.
- There is an increase in energy expenditure after exercise
(after burn) – can increase metabolic rate for up to 24hrs.
- Exercise minimises muscle loss – muscles burn more calories.
- Exercise maintains or increases muscle mass which although it
adds weight is usually beneficial to performance, and is
certainly beneficial for increasing RMR (resting energy
expenditure).
- Prolonged aerobic exercise mobilises fats for energy usage.
- Above points have the effect of increasing the RMR – energy
usage at rest.
- There is some evidence that exercise suppresses appetite
(potentially decreasing energy intake).
Exercise intensity for fat loss
- Duration should be at least 20-30 mins to allow the metabolism
of fats.
- For optimum fat burning, exercise intensity should be lower.
- This encourages the usage of fats for energy instead of
carbohydrates (glycogen/glucose).
See graph on p482 0f textbook. This will show you the suggested
intensity of the fat burning zone.
Effects of dieting on body composition
Decreasing diet alone (and not increasing exercise) may decrease
the fat mass, but it will also likely result in a decrease in lean body
mass and therefore RMR – effect is the slowing of the metabolic
rate (detrimental to weight loss).
By increasing exercise and energy expenditure with too great a
reduction in energy intake, performance can be reduced due to lack
of energy.
Age and body composition
- The body’s rate of burning calories (metabolic rate) decreases
with age.
- Partly due to decrease in muscle mass, and increase in fat
mass.
- This has a negative effect on metabolic rate. At the same time
diet (energy intake) remains the same. This can have only one
result – more body fat!
- As we get older the trend is foe a more sedentary/less active
lifestyle.
- Regular exercise will help to increase/maintain energy
expenditure and RMR.