Human Energy
What is energy?
o Energy
is the capacity to do work
n
May be in the form of:
p Mechanical
p Light
p Nuclear
p Electrical
p Heat
p chemical
How do we measure energy?
o Work
= force x distance
o Power
= work/time
n
How fast work is done
o Units
n
English
n
Metric
n
System of International units (SI)
p Eventually
hope to move all measures of energy to this system
Chemical Energy
o How
many calories are in food? How did we
find out?
n
Bomb calorimeter
p Measures
the amount of heat given off from food that is combusted in a chamber
surrounded by water
p This
heat measurement gives us calories if we remember that:
n
A Calorie = amount of heat needed to
raise the temperature of 1 kilogram of water, 1OC
Energy yields from calorimeter
o
1 gram CHO = 4.3
calories
o
1 gram Fat = 9.45
calories
o
1 gram Protein =
5.65 calories
o
1 gram Alcohol =
7.0 calories
After digestion:
o
1 gram CHO = 4.0
calories
o
1 gram Fat = 9.0
calories
o
1 gram Protein =
4.0 calories
o
1 gram Alcohol =
7.0 calories
Chemical “Human” Energy
o
How do we measure
calories that we expend from exercise?
n
Use of O2
measurement devices
p Metabolic cart
n
Its oxygen
analyzers measure amount of O2 that we consume during exercise;
picked up through expired gases via tubing from mouth
n
1 liter of O2
consumed ~ 5 Calories burned
n
Use of
doubly-labeled water
p Labeled water with H2 and O2 is
ingested
n
Urine and blood
samples are measured for H2 and O2
o
Labeled O2
is eliminated as water and CO2
o
Labeled H2
is eliminated as only water
o
Subtract H2
losses from water which gives measure of CO2; the CO2 is
converted to energy expenditure
Energy in the Body
o ATP
n
Immediate form of energy
n
Stored in small amounts in a variety of tissues
o Phosphocreatine
(PCr)
n
Rapidly replenishes used ATP
n
Not an immediate source of energy
n
Stored in small amounts
How are ATP derived from CHO, Fat, and Protein
Protein CHO Fat
The Energy Systems Necessary for Exercise
o
ATP-PC System
n
Phosphogen system
p Direct source of ATP for quick energy
p Supplies energy for “max” events of 0 -10 seconds
p ATP used for energy; PC replaces lost ATP
o
Lactic Acid
System
n
Anaerobic
glycolysis (breakdown of glucose without use of O2) [glucose lactic acid]
n
Rebuilds ATP
quickly for events of “near-maximal” efforts (30-120 seconds)
n
Lactic
acid, resulting from glucose breakdown, can be used by other tissues as an
energy source
The Energy Systems Necessary for Exercise
o
Oxygen system
n
Aerobic system
p Produces ATP in large quantities from several energy
sources in the body
n
e.g. muscle &
liver glycogen; blood glucose & FFA; triglycerides in muscle, blood &
adipose tissue; and body protein
p Rebuilds ATP for sporting events of long duration from
5 km (3.1 mi) to marathon and beyond
p Sometimes subdivided as:
n
Aerobic glycolysis
– glucose + O2 for energy
n
Aerobic lipolysis
– fat + O2 for energy
Other nutrients responsible for energy metabolism
o
Water
n
Helps break up
(hydrolysis) and transform necessary energy compounds
o
Vitamins
n
Needed for energy
release from cells
n
e.g. - Niacin
serves in glycolysis
- Thiamin needed to convert products
to acetyl-CoA
o
Minerals
n
Essential for
cellular processes
n
e.g. - Iron
needed for proper utilization of O2
- Calcium needed to initiate muscle contraction
Metabolism
o
Sum total of all
physical and chemical changes that take place within the body
o
Involves 2
processes:
n
Anabolism –
building-up process
n
Catabolism –
tearing-down process
o
Metabolic rate –
how rapidly the body uses its energy stores
n
Accounted for by:
p Resting energy expenditure
p Energy expenditure due to eating a meal
p Physical activity
Metabolism
o Basal
Metabolic Rate
n
The energy requirements of the cellular and
tissues processes that are necessary to continue physiological activities in a
resting, postabsorptive state throughout the day
n
It is the lowest rate of energy
expenditure
n
Determined by measuring O2 while in a
reclined position, after a 12-hour fast
Metabolism
o Resting
Metabolic Rate (RMR) or Resting Energy Expenditure (REE)
n
Represents the BMR + small amounts of energy
expenditure associated with previous muscle activity
n
Slightly higher caloric expenditure than BMR
(< 10% difference)
Effect of Eating on Metabolic Rate
o Metabolic
rate raises resulting in what is called dietary-induced thermogenesis (DIT) or
thermic effect of food (TEF)
n
Increased caloric expenditure due to:
p Absorption,
transport, storage, and metabolizing the food consumed
p Highest
about 1 hour after a meal and lasts up to about 4 hours
n
The greater the caloric content of food, the
greater the TEF effect
Effect of Eating on Metabolic Rate
o The
DIT or TEF:
n
Affected by type of food:
p TEF
for protein ~ 25%
p TEF
for CHO ~ 8%
p TEF
for fat ~ 4%
n
The TEF from a mixed meal of CHO, Fat, and
Protein is ~ 5-10% above RMR
n
One study suggests that obesity is associated
with a decreased TEF; obese appear to store fat more efficiently.
Estimating your RMR (or REE)
o
May determine
rough estimate by:
n
1 Calorie per kg
of body wt per hour
p e.g. For a 70
kg male
1 x 70 kg x 24 hr = 1,680 Cal per day
for an average range + or –
10%
e.g. 1,680 x .10 = 168
so
1,680 + 168 = 1,848
and
1,680 – 168 = 1,512
Range for caloric need at rest is 1,512 to
1,848 Cals
Genetic Factors Affecting REE
o
Age
n
REE much higher in
children
o
Gender
n
REE ~ 10-15% lower
in women than men
o
Natural hormonal
activity
n
REE higher with
greater thyroid activity
o
Body size and
surface area
n
REE lower in
leaner individuals; these individuals lose more body heat via radiation
o
Body composition
n
Amount of fat vs
fat-free tissue
p Muscle is more metabolically active so muscular person
has higher REE
Body composition effect on REE
o Larger
individuals have higher REE
n
Loss of weight results in a reduction of REE
p Reduction
in REE with weight loss may be accompanied by lower level of thyroid hormones
p It
is possible to maintain weight through loss of weight but gain in muscle mass;
this may keep REE from changing or elevate it.
Environmental Factors affecting REE
o Caffeine
↑
o Smoking ↑
o Exposure to
cold environments ↑
o Exposure to
hot environments ↑
o Higher
altitude ↑
o Exercise ↑
Energy Sources Used at Rest
o Primarily
CHO and Fat
n
From a mixed diet of CHO, Fat, & Protein 60% of REE is derived from fat
40% of REE is derived from CHO
n
From diet rich in CHO
p Greater
% of REE derived from CHO
n
From diet rich in Fat
p Greater
% of REE derived from Fat
Effect of Exercise on
Metabolic Rate
o Exercise
raises metabolic rate (energy expenditure)
n
Known as Exercise Metabolic Rate (EMR)
p Also
known as Thermic Effect of Exercise (TEE)
n
Dependent upon:
p Fiber
types
n
Type I or slow-twitch
n
Type II a or fast-twitch with both aerobic and
anaerobic properties
n
Type II b or fast-twitch with anaerobic
properties
Effect of Exercise on
Metabolic Rate
o Factors
affecting metabolic rate
n
Intensity or speed of the exercise
p Primary
factor
p High
speeds increase caloric expenditure exponentially
n
Efficiency of movement
p Less
efficient, more calories burned
n
Body weight
p Greater
body weight, more calories burned
How is energy expenditure expressed?
o
Calories per
minute
o
Kilojoules
n
1 Calorie = 4 kJ
o
Oxygen uptake
n
1 liter of O2
consumed = 5 Calories burned
o
METS
n
Unit of energy
that represents multiples of RMR
p 1 MET = 3.5 ml of O2 consumed per kilogram
of body weight per minute (ml/kg/min)
Calculation of Energy Expenditure
o
When measuring O2
from a treadmill run, a 154 lb individual achieves a value of 25 ml/kg/min at
maximal effort. What is the MET level
and rate of calories being burned?
n
Steps to solve:
p 25 ml/kg/min divided by 3.5 = 7.14 METs
p Convert 154 lb to kg; 154/2.2 = 70 kg
p
Determine
total energy cost; 70 x 25 = 1,750 ml of O2
p Convert ml to L; 1,750/1000 = 1.75 L of O2
p Multiply 1.75 x 5 = 8.75 Calories/min
Best Activities for Caloric Expenditure
o
Intensity and duration
are the key determinants of total energy expenditure
o
Walking and
running are most popular
n
Slow, leisure
walking expends ½ of the calories
of running per 1 mile distance
n
Making walking more vigorous
p Walk faster, climb stairs, use 1-3 lb hand-held wts (can ↑ energy expenditure by 5-10%)
p Walking with ankle wts not advised (possible injury)
o
Swimming has ~ 4 times the energy expenditure of
running the same distance (i.e. ¼ mi swim = 1 mile
run)
o
Bicycling has ¹/³ energy expenditure cost as running
o
Aerobic Dance can expend about 9-10 Calories per
minute
Energy Expenditure after Exercise
o
Caloric
expenditure remains elevated after
exercise
n
Often known as
Excess post-exercise oxygen consumption (EPOC)
n
Dependent on
intensity and duration of activity
n
May remain
elevated from 15-20 minutes up to 4-5 hours; some suggest even longer
n
Weight training
appears to exhibit greater EPOC response compared to other activities
p Primarily due to level of resistance
Does Exercise have an Effect on the TEF?
o No
definitive findings yet to say that it increases or decreases the TEF
n
If any changes occurs, the ↑ or ↓ only amounts to 5-9
Calories over several hours
What does the total daily energy expenditure look like?
Human Energy Spectrum (% contribution of
energy systems to different time periods of Max Work)
Fatigue
o A
condition of physiological and/or psychological state of tiredness or showing a
lack of energy to perform.
Potential Fatigue Sites
o
Central Locations
o
Brain
o
Spinal Cord
o
Peripheral Locations
o
Neuromuscular junction
o
Muscle cell
(primary suspect)
Possible Causes of Fatigue during Exercise
o Increased
formation of depressant neurotransmitters
o Decreased
levels of energy substrates
o Disturbed
intracellular environment
o Disturbed
acid-base balance
o Decreased
O2 transport
o Increased
core body temperature (dehydration)
o Disturbed
electrolyte balance
Can Fatigue be delayed?
o Yes
o Use
of proper physiological, psychological, and biomechanical training are the best
means to deter premature fatigue
Is Nutrition related to Fatigue Processes?
o
Yes
o
For low-level
aerobic activity (longer than 2 hours)
n
Need fat and CHO
stores
o
For moderate to
heavy aerobic activity (1-2 hrs)
n
Need CHO stores
o
For
high-intensity (1-2 min)
n
Need good
buffering system (bicarbonate)
o
For extreme
high-intensity (5-10 sec)
n
Need good
phosphate operating system