Download Energy Sources for Physical Performance

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TOPIC 1: Energy Sources for Physical Performance
TOPIC 1:
ENERGY SOURCES FOR
PHYSICAL PERFORMANCE
1.1 Sources of Nutrients: Carbohydrates, Fats, and Proteins
1.2 Chemical Breakdown of Nutrients: Glucose, Glycogen, Free Fatty Acids
1.3 Aerobic & Anaerobic Energy: ATP-CP, Lactic Acid & Oxygen Systems
1.4 Contribution of Energy Systems for Specific Activities
1.5 Acute Responses to Exercise: Responses in the Circulatory, Respiratory, and
Muscular Systems to Provide Energy
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TOPIC 1: Energy Sources for Physical Performance
1.1 Sources of Nutrients: Carbohydrates, Fats, and Proteins
Carbohydrates:
After carbohydrates are eaten, they are broken down into the digestive tract and absorbed into the blood
as simple sugars (with the glucose molecule being the most common sugar). This absorption occurs in the
small intestine because it is the easiest point for the blood to pick up the glucose molecules. Once a glucose
molecule enters the blood, it either travels around the blood in the form of glucose or it is stored as
glycogen in the muscles. Once muscle stores are full, excess glucose is transported to the liver where is can
be stored as glycogen. Glycogen stored in the liver can be converted back to glucose to maintain blood
glucose levels, or it may be transported (via the blood) to various muscles as required.
Blood glucose (with glycogen) is a major fuel for intense exercise. Two-thirds of the glucose that is stored as
glycogen is found in the muscles. This enables the muscles to have the glucose stored “on-site” and ready
to be used. Glycogen is the fuel primarily used for high intensity activity. If muscle and liver glycogen stores
are full, excess glucose is converted into triglyceride (fat) and stored in then body as adipose tissue (fat
cells).
Fats:
Fats are a major food source for prolonged moderate exercise. They also provide two-thirds of the body’s
fuel requirements when at rest. The majority of fat is digested in the small intestine where, under a process
called hydrolysis, it is broken up into smaller molecules called monoglycerrides (fatty acids and glycerol).
Once absorbed by the intestine, the fatty acids and glycerol combine to form triglycerides – three fatty acid
molecules added to one molecule of glycerol.
Triglycerides can be stored either in skeletal muscles or adipose tissue (fat cells that provides heat or
insulation). Where necessary they will release the fatty acids to the transported by the blood to the
working muscles.
Protein:
Protein only minimally contributes to the production of energy. Only in extreme circumstances (such as
starvation or ultra marathon events) when the body has severely depleted its supplies of carbohydrates
and fats, protein becomes a viable source of energy. Amino acids found in protein rich foods are the
building blocks of the human body and are used for muscle growth and repair.
The Body’s Storage of Food Fuel:
Food Source
Carbohydrate
Fat
Protein
Stored as
Site
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TOPIC 1: Energy Sources for Physical Performance
Approximate Fuel and Energy Stores in the Body
(Assuming Subject Mass 65kg with 15% Body Fat)
The amount of energy stored in the two main nutrient fuels is as follows:
 Fats (1g)
= 37kj (9 cal)
 Carbohydrates (1g)
= 17kj (4 cal)
Nutrient
Amount stored (g)
1. Carbohydrate
Blood glucose
Muscle glycogen
Liver glycogen
15g
250g
110g
Total Carbohydrate
375g
2. Fat
Adipose tissue
Intramuscular
7800g
160g
Total fat
7960g
Calculate the ‘energy stored’ in the table above.
Energy stored (kj)
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TOPIC 1: Energy Sources for Physical Performance
1.2 Chemical Breakdown of Nutrients: Glucose, Glycogen, Free Fatty Acids
The energy stored in foods is not used directly by the body for biological work. Instead this energy is
released to rebuild a chemical compound called adenosine triphosphate (ATP). ATP is the ‘energy currency’
of the human body. ATP is an energy rich molecule that consists of an adenosine molecule and three
phosphate molecules chemically joined together. The breaking away of one of the ‘high energy’ phosphate
bonds form adenosine diphosphate (ADP) and releases the energy required for all forms of biological work.
This process is reversible, meaning ADP + P can be resynthesised to reform ATP, but it requires energy.
Carbohydrates (Glucose and Glycogen)
Carbohydrates require considerably less ‘work’ (less oxygen) to breakdown, glycogen usage tends to be
dominate with intense exercise. For this reason, carbohydrates are considered the body’s primary fuel. For
a marathon runner, the preferred fuel is still glycogen, but the body’s stores of carbohydrate are limited. If
the athlete runs out of glycogen the body must utilise fatty acids as the major fuel source.
Fats (Free Fatty Acids)
Fats are larger molecules requiring more ‘work’ (more oxygen) to breakdown. It is harder work for an
athlete who is trying to breakdown fat and as a result their performance will decline. They will find it
difficult to concentrate and may appear disorientated; this term is ‘hitting the wall’. Therefore fats tend to
be more dominant at low intensity when oxygen delivery is not a limiting factor.
Resynthesis of ATP
Carbohydrates and fats are the main nutrient fuels used to supply the energy needed to the resynthesise of
ATP, but the relative contribution of carbohydrates and fat as a fuel will depend to a large degree on the
exercise duration and intensity.
Fats can only be broken down to resynthesis ATP in a process requiring oxygen called aerobic lipolysis.
Carbohydrates can be broken down aerobically in a process called aerobic glycolysis, but they may also be
broken down without oxygen (anaerobically) in a process called anaerobic glycolysis.
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TOPIC 1: Energy Sources for Physical Performance
1.3 Aerobic and Anaerobic Energy: ATP-CP System, Lactic Acid System, Aerobic
System.
Adenosine Triphosphate (ATP)

The energy required by the body to sustain life and for the contraction of muscles to produce
movement is derived from the food we eat.

When food is digested, it is broken down into CHEMICAL COMPOUNDS including carbohydrates, fats,
and proteins. These chemicals compounds contain energy.
FOOD
Carbohydrates

Fats
Proteins
The energy contained in carbohydrates, fats, and protein cannot be used directly by the body. Instead it
is used to form a chemical compound called ADENOSINE TRIPHOSPHATE (ATP).
ATP:
ADENOSINE


P
P
P
ATP is stored in small amounts in all muscle cells.
It is the energy released, during the breakdown of ATP into ADENOSINE DIPHOSPHATE (ADP) and the
third PHOSPHATE, which represents the immediate source of energy that can be used by the muscle
cells to perform work.
Breakdown of ATP into ADP + P:
ADENOSINE
P
P
P
ENERGY RELEASED
ATP → ADP + P
Sources of ATP:



ATP can be stored in the muscles in only small amounts.
Once this store has been used up, the body must supply the muscle with more ATP for it to continue
working.
The supply of ATP is limited by the intensity and duration of the physical activity.
PRIMARY SOURCE OF ATP: carbohydrates, which are broken down to glucose and glycogen.
SECONDARY SOURCE OF ATP: fats, which are broken down into free fatty acids.
EXTREME SOURCE OF ATP: proteins, only under extreme conditions.
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TOPIC 1: Energy Sources for Physical Performance
Sources of Energy to Perform Work
IS DIGESTED INTO
USED TO FORM CHEMICAL COMPOUND
ATP
CHEMICAL ENERGY
BREAKING OF PHOSPHATE BONDS GIVES ENERGY
BREAKING OF PHOSPHATE BONDS
GIVES ENERGY
ADENOSINE
P
P
P
ENERGY RELEASED
→
ENERGY RELEASED IS USED BY MUSCLES TO WORK
ENERGY RELEASED IS USED BY
MUSCLES TO WORK
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TOPIC 1: Energy Sources for Physical Performance
The ATP-CP System
Small amounts of ATP are stored in the muscles. Energy is released when the chemical bonds (phosphate
bonds) of the ATP are broken.
Adenosine triphosphate has 3 phosphates. One of these breaks away to leave adenosine diphosphate (ADP)
and a single phosphate: ATP → ADP + P
When exercise begins, ATP stored in muscles is used to release energy for muscular contraction. However,
the stores of ATP are limited, and if exercise continues, the ADP and Phosphate must be recombined to
produce more ATP.
The body has the ability to remake ATP as quickly as it is broken down by using another Phosphate fuel
called creatine phosphate (CP) which is also stored in muscles. Creatine phosphate is broken down into
creatine and phosphate, releasing energy which is used to rejoin ADP and phosphate to form ATP.
Unfortunately, stores of CP in the muscles are also limited, so the energy formed via this system only lasts
for about 10 seconds of high intensity exercise, and is not replenished until approximately 2-3 minutes of
rest.
For this reason, the ATP-CP system is the predominate energy system for producing ATP for sudden bursts
of activity that takes less than 10 seconds such as a high jump, a tennis serve, a short sprint, or a javelin
throw.
The ATP-CP system relies on stores that are readily available in the muscles and therefore energy can be
released the moment it is required. The body does not have to go through a complex set of reactions. It is
the most immediate source of ATP, providing energy for muscular contraction at the commencement of an
activity.
The ATP-CP system is also known as the ATP-PC system, Alactacid system and Phosphagen system.
The ATP-CP System
ATP
STORES IN MUSCLE
ATP
RECOMBINED
ADP + P → ATP
ATP → ADP + P
ENERGY
RELEASED
ENERGY
RELEASE
D
MUSCLE
CONTRACTION
CP → C + P
CP STORES
IN MUSCLES
TOPIC 1: Energy Sources for Physical Performance
The Lactic Acid System
If exercise continues beyond 10 seconds, the stores of ATP in muscles are exhausted. The body must
therefore resort to an alternative source of ATP, and the second of the energy systems in the anaerobic
pathway takes over. This is the Lactic Acid system.
The Lactic Aacid system uses carbohydrates from the food eaten, as the fuel for manufacturing ATP.
Carbohydrates are converted into glucose which is transported by the blood to the muscles and liver to be
stored as glycogen.
With the aid of enzymes (proteins which initiate specific chemical reactions), the glycogen is converted into
a substance called Lactic Acid. During this reaction, energy is released, and this energy is used to recombine
the ADP and Phosphate to ATP.
Only 2 ATP molecules are produces for each glucose molecule. Unfortunately, like the ATP-CP system, the
Lactic Acid system is functional only for a limited time.
The Lactic Acid produced by the chemical reaction is toxic in large amounts. As it begins to build up in the
muscles, discomfort and fatigue set in. An often quoted example of this is the feeling of heavy legs in the
home straight of a 400m sprint. This is a symptom of lactic acid build-up. The Lactic Acid system therefore
provides ATP for high intensity activities lasting between 30 seconds to 2 minutes, such as a gymnastics
floor routine, a 400m sprint, or a 200m swim.
If exercise is to be maintained beyond this time, its intensity must be reduced as the rapid production of
ATP through the Lactic Acid system cannot be sustained for very long, and the accumulation of lactic acid in
the muscles will prevent continued efficient muscle contraction at high intensity.
The Lactic Acid system is also known as Anaerobic glycolysis (the breakdown of glucose without oxygen)
and Lactacid system .
The Lactic Acid System
CARBOHYRDATE
ATP
RECOMBINED
GLUCOGEN STORED
IN MUSCLE
ADP + P → ATP
ACTION OF
ENZYMES
ENERGY
RELEASED
BY
PRODUCT
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LACTIC ACID
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TOPIC 1: Energy Sources for Physical Performance
The Aerobic Energy System
After 2 to 3 minutes of exercise, respiratory rate, tidal volume, heart rate, stroke volume, cardiac output
and arteriovenous oxygen difference all increase sufficiently to supply the working muscles with enough
oxygen to produce ATP aerobically.
Aerobic production of ATP can involve the breakdown of carbohydrate, fat or protein to release large
amounts of ATP (32 molecules of ATP for each molecule of glucose). The by-products of the reaction are
carbon dioxide and water.
Carbohydrates can provide sufficient fuel for about 2 or 3 hours of exercise, after which time the body
needs to look for alternative sources of fuel. Exercise can be continued by using the reserve fuel (fat). To
produce energy from fat, requires far more oxygen than to produce the same amount of energy from
carbohydrate.
For the same rate of energy production is to be maintained, the cardio-respiratory system will be overtaxed
in delivering the additional oxygen required for the breakdown of fat. As a result the athlete will become
breathless, fatigued and will eventually have to reduce intensity of exercise or stop.
Protein is used as a fuel for ATP production only in extreme cases of prolonged physical work. Ultra
marathons of 4 – 5 days duration would rely on protein to provide ATP in the final stages of the event.
The Aerobic system is also known as the Oxygen system, Aerobic glycolysis (the breakdown of carbohydrate
in the presence of oxygen) and Aerobic lipolysis (the breakdown of fat in the presence of oxygen).
The Aerobic Energy System
GLYCOGEN
FATS
PROTEIN
WITH SUFFICIENT
OXYGEN
ENERGY
RELEASED
USED TO RECOMBINED
ATP MOLECULE
ADP + P → ATP
All Systems Go Again
ATP
BY
PRODUCT
CARBON
DIOXIDE
BREATHED OUT
WATER
PERSPIRATION
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TOPIC 1: Energy Sources for Physical Performance
Watch ‘All Systems Go Again’ on Click View and answer the following questions:
ATP-CP System
1. What does the term anaerobic mean?
2. What is the role of Creatine Phosphate?
3. State a time span for this particular energy system. Give 4 examples of sports where the energy for this
activity is predominantly provided by this reaction.
Lactic Acid System
4. What do you understand by the term ‘glycogen’?
5. State a time span for this particular energy system. Give 4 examples of sports where the energy for this
activity is predominantly provided by this reaction.
Aerobic Energy System
6. Why does your heart rate and breathing rate increase whilst you are exercising aerobically?
7. What is the downside of using fat as the fuel for aerobic glycolysis?
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TOPIC 1: Energy Sources for Physical Performance
8. State a time span for this particular energy system. Give 4 examples of sports where the energy for this
activity is predominantly provided by this reaction.
Interplay of energy systems
9. Using relevant examples, describe why just one energy system is not solely used in most team games?
10. Define the term VO2 max and state the units it is measured in.
11. What are the average levels for VO2 max for an average sedentary male and an elite endurance athlete?
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TOPIC 1: Energy Sources for Physical Performance
Pathways for Energy Production
ANAEROBIC PATHWAY
ATP-CP
ENERGY SYSTEM
AEROBIC PATHWAY
LACTIC ACID
ENERGY SYSTEM
AEROBIC
ENERGY SYSTEM
Summary of the 3 Energy Systems:
Characteristic
1. Oxygen
requirements
for energy
source
reaction
2. Energy source
for ATP
production
ATP-CP System
Lactic Acid System
Aerobic System
Anaerobic – no oxygen
required
Anaerobic – no oxygen
required
Aerobic – oxygen required
in the reaction
Chemical fuel - Creatine
Phosphate (CP)
Food source Carbohydrates
Glycogen
Food source Carbohydrates
Fat
Protein
3. Duration of
energy system
4. Intensity
5. Recovery time
until repeat
effort
6. Factors when
operating
maximally
7. Specific
sporting
examples
8. Everyday
activity
examples
CP replenishments: 3-5
minutes
 50% in first 30 secs
 Rest recovery best
Depletion of ATP and CP
stores
Removal of lactic acids to
rest levels.
 With active recovery:
- 50% removal in 15 mins
- 95% removal in 30 mins
 With passive recovery:
- 50% removal in 30 mins
- 95% removal in 60 mins
Lactic acid accumulation
Restoration of body
glycogen stores:
 After competition of
more that 1 hr: 2448hrs
 After hard interval
training: 6-24hrs
By product of water and
carbon dioxide
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TOPIC 1: Energy Sources for Physical Performance
Positives & Negatives of Energy Systems
The ATP-CP System
Positives
Negatives
The Lactic Acid System
Positives
Negatives
The Aerobic System
Positives
Negatives
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TOPIC 1: Energy Sources for Physical Performance
Maximum Oxygen Consumption (VO2 Max)
VO2 Max = the volume of oxygen consumed by the body for energy production. It is measured in litres of
oxygen consumed per minute (L/min).
If an athlete were to slowly increase exercise intensity, there would be a corresponding increase in oxygen
consumption until they reached maximum oxygen consumption (VO2 Max) – the region where oxygen
uptake peaks despite further increases in exercise intensity (refer to the following diagram).
Because larger people tend to consume more oxygen than smaller people (purely because of their larger
size), VO2 Max is usually expressed as a relative VO2 Max in millilitres of oxygen consumed per kilogram of
body weight per minute (ml/kg/min). This allows for the comparison of different-sized individuals. For
example, in the following diagram the athlete’s peak VO2 Max value was 3.6 litres per minute. If the athlete
undergoing this test had a mass of 68kg, then their average relative oxygen consumption would be
calculated as follows:
3.6L/min x 1000 = 3600ml
3600/68kg = 52.9ml/kg/min
The VO2 Max is an important indicator in determining a person’s capacity for the aerobic resynthesis of
ATP, with elite endurance athletes having higher values than other sports performers. Untrained individuals
would have a VO2 Max of approximately 40ml/kg/min, while values exceeding 70ml/kg/min or beyond are
only achieved by superbly conditioned endurance athletes.
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TOPIC 1: Energy Sources for Physical Performance
Anaerobic Threshold (AT)
Anaerobic Threshold (AT) is the maximum intensity of steady state exercise (% VO2 max) that a person can
sustain without a rapid increase in the accumulation of lactic acid.
It should be noted that exercise intensities approaching VO2 max can only be achieved through the
dominant use of the lactic acid system with subsequent formation and accumulation of lactic acid.
Generally speaking, the most common reference point for anaerobic threshold is thought to be when blood
lactate levels exceed 4 ml per litre of blood.
Because there is no actual threshold point where aerobic processes simply ‘stop’ and anaerobic processes
simply ‘begin’, anaerobic threshold is more correctly referred to as the Onset of Blood Lactic-acid
Accumulation (OBLA).
A person’s anaerobic threshold, or OBLA, has a large impact on the athletic performance. It determines the
maximum exercise intensity they can maintain for an extended period of time without the fatiguing effects
of lactic acid accumulation. Generally speaking, individuals with higher AT or OBLA values (expressed as a %
of their VO2 max) are the better endurance performers. Through training, VO2 max and anaerobic threshold
can be improved.
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TOPIC 1: Energy Sources for Physical Performance
1.3 Aerobic and Anaerobic Energy: ATP-CP System, Lactic Acid System, Aerobic
System.
Oxygen Deficit
Oxygen Deficit = the period of time at the start of exercise where the level of oxygen consumption is below
the necessary level to supply ATP aerobically. Because it takes 2-3 minutes to increase the O2 supply
sufficiently, the two anaerobic systems must provide the required ATP during this time, thus creating an
oxygen deficit.
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TOPIC 1: Energy Sources for Physical Performance
Oxygen Debt or Excess Post-Exercise Oxygen Consumption (EPOC)
Oxygen Debt or EPOC = the period of time after exercise where O2 consumption will remain elevated to
allow the body to slowly return to pre-exercise levels. During this stage, the heart and lungs continue to
deliver O2 to the body to rebuild energy supplies. This is usually seen at the end of a race where a runner
will pant vigorously.
There 2 components of EPOC:
ALACTACID COMPONENT (fast) = the O2 consumed in early recovery to replenish ATP-CP stores and to resupply oxygen bound to myoglobin. This process is accomplished very quickly; 30 seconds for 50%
replenishment and 3 minutes for 100%.
LACTACID COMPONENT (slow) = the extra O2 is consumed and used to breakdown and remove lactic acid
that has accumulated, resynthesise glycogen, restore body temperature and normal breathing. This process
can take 1-2 hours to be completely repaid, however an active recovery can speed up the process.
Continuous activity post-exercise (at about 55-60% VO2 max) will speed up the removal of lactic acid.
o It prevents blood pooling in the extremities
o It allows the skeletal muscles to oxidise some of the lactic acid for energy (70%)
o An elevated heart rate keeps blood circulation to the liver high, assisting with the
conversion of lactic acid back to glycogen.
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TOPIC 1: Energy Sources for Physical Performance
1.4 Contribution of Energy Systems for Specific Activities
Interplay of Energy Systems
At any one time, all three energy systems will be functioning. It is the intensity of exercise (how quickly ATP
is required) and the duration of exercise (how much ATP is required) that will determine which energy
system(s) will be dominant in any activity. As exercise intensity increases there is a greater reliance on the
more powerful anaerobic systems and as the duration of exercise increases (to around 2 minutes or more),
the dominant energy system will become more aerobic in nature.
The above diagram shows how the three systems vary in their percentage contribution to energy/ATP
production depending on the duration of the activity.
During a football or netball match, what would the energy system contribution be for key centre players who
may not be working maximally for extended periods of time? As soon as the players start moving, the
ATP−PC system starts providing energy. This system reaches its peak within the first five seconds, at which
point the other anaerobic system – the lactic acid system – becomes the major supplier of ATP. The
ATP−PC system continues to supply energy, but is limited by the amount of PC and will be totally drained
after 12 to 15 seconds.
As the players keep moving on the field or court, the aerobic system increases its contribution and takes
over from the lactic acid system as the major energy system contributor at one to two minutes into play.
Oxygen can be made available to working muscles at a much quicker rate than previously thought. Explosive
energy for short sprints and rapid movements is provided by the lactic acid system as the ATP−PC system
has not had an opportunity to recharge. However, ATP is provided by the aerobic system in large quantities
even during high-intensity activities.
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TOPIC 1: Energy Sources for Physical Performance
Example 1
In a 6 second dash to escape from a vicious dog, the subject running at high speed will utilise
predominantly the ATP-CP system. Yet, the other two systems will contribute something even if extremely
little.
Therefore, the ATP-CP energy system will be the dominant energy system.
Note that if the subject is still running at a high speed after 60 seconds, the contribution of the ATP-CP
energy system has drastically fallen, being replaced as the dominant energy system by both the Lactic Acid
system and Aerobic system.
Example 2
In a 200m sprint at the elite level, the intensity suggests the anaerobic energy systems as the dominate
source of energy. The duration of the event points more to the lactic acid system because after 10 seconds
the majority of the CP stores have been exhausted.
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TOPIC 1: Energy Sources for Physical Performance
1.5 Acute Responses to Exercise: Responses in the Circulatory, Respiratory and
Muscular Systems to Provide Energy
Complete the following task using your text books:
1. Define the following terms:
a. Acute response
b. Chronic response
2. For each of the terms below:
a. Define the term.
b. State how it changes.
c. State why it changes.









Heart Rate
Stroke Volume
Cardiac Output
A-v O2 Difference
Blood Pressure
Tidal Volume
Ventilation
Oxygen Uptake
Blood Volume
Complete the following Laboratory Activity:
Perform the following activities, taking your pulse for 15 seconds immediately after you complete each
activity.
a.
b.
c.
d.
Walking for 2 minutes
Running for 2 minutes
Set-ups on a bench for 2 minutes
Bent-knee sit ups for 2 minutes




Record and graph results. Multiply by 4 to determine your heartbeats per minute.
Identify which exercise caused the highest heart rate.
Discuss the relationship between your heart rate and the intensity of your activity.
Explain why you should not measure your pulse rate with you thumb.
Then: