Ergometry and the Energetics of Exercise An ergometer is any device that measures the amount of mech

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PT2 Aerobic Work Capacity 2005
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Oxygen (VO2) utilisation/uptake at restThe VO2
at rest is often referred to as a METOne MET is
equivalent to 3.5 ml/kg/minie. mls of oxygen per
kilogram of bodyweight per minuteThis expresses
VO2 relative to the bodyweight of the person.
We all use approximately 3.5ml/kg/min (1 MET) at
rest
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Average resting values VO2
3.5ml.kg-1min-1 CO 5 6
litres.min-1 HR varies with fitness
65 75 bpm SV varies with fitness
85 ml
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CO HR X SV At
rest 6.0 litres 70 X
? therefore SV 85.7ml Thus if a
person has a low resting heart rate then this
reflects a high stroke volume and conversely if
a person has a high resting heart rate this
reflects a low stroke volume.
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The total volume of oxygen we use per minute at
rest however depends on our bodyweight.Thus a
60kg person uses approximately 210ml of oxygen
per minute at rest 60kg X 3.5ml/kg/min
210ml/minNote One litre of oxygen utilised
is equivalent to 21kJ of energy expended. The
exact amount of energy expended is dependent on
the substrate oxidised (carbohydrate, fat,
protein)
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Thus a 60kg person uses 4.41kJ/minute of energy
at rest (0.210 litres/min X 21kJ)Similar
estimations of energy expenditure for physical
occupational work tasks and exercise can be made
if the VO2 is known.Note there is a direct
linear relationship between the power output and
the VO2utilised in steady state physical
activity
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Steady state exercise occurs when the energy
demand of physical activity is adequately met by
oxygen delivery to the exercising muscles.Since
the kinetics of oxygen delivery to the exercising
muscles is relatively slow at the beginning of
physical activityit may take 2-3 minutes before
a steady state is established.Note there is
also a linear relationship between the heart rate
and the power output during steady state
exercise.
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VO2
Power
HR
Power
HR
VO2
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Relationship between HRmax and VO2max
HRmax VO2max
50 28
60 40
70 58
80 70
90 83
100 100
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Note the VO2 (litres/min) cost of exercising on
a cycle ergometer is the same for all individuals
at a given power outputirrespective of age,
gender and state of training. However the heart
rate response may vary considerably between
individuals because of differences in fitness
(stroke volume of the heart) There are
considerable differences between individuals
however in the VO2 (ml/kg/min) cost of running
less so with walking and bench stepping exercise.
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uneconomical
VO2 ml/kg/min
economical
Running velocity
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Based on the relationship between power and VO2,
linear regression equations are used to predict
the VO2 cost of exercise. The energy
expenditure/cost of exercise (walking, running,
cycling, bench stepping) can then be
estimated. A simple short cut estimate of the
energy cost of walking is
0.5kcal/kg/km And for running
1.0kcal/kg/km Note 1.0kcal 4.2kJ

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Example Lidcombe railway station to Cumberland
campus and return is 4.0 km. Therefore the
energy cost of walking this distance is 0.5 x
b/wt x 4.0 50kg person is 100Kcal (420kJ) 55kg
person is 110Kcal (462kJ) 60kg person is 120Kcal
(504kJ) 65kg person is 130Kcal (546kJ) 70kg
person is 140Kcal (588kJ)
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Note that a Tim Tam chocolate biscuit is
equivalent to 760kJ of energy. Therefore this
provides enough energy for 50kg person to walk
7.24 km (or rest for 207 min) 55kg person to
walk 6.58 km (or rest for 188 min) 60kg person
to walk 6.03 km (or rest for 172 min) 65kg
person to walk 5.57 km (or rest for 159
min) 70kg person to walk 5.17 km (or rest for
148 min)
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Energy expenditure for a physical task may exceed
prediction equations if the efficiency of
movement is perturbed eg. air resistance/wind,
sandy surface, heavy boots etc Swimming includes
a significant skill component that effects the
VO2 cost. Pedal cadence has a small effect on the
VO2 cost of cyclingbut incorrect seat height has
a significant effect
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Steady state
VO2 deficit
EPOC
VO2
time
3.5ml/kg/min
Note anaerobic sources of energy contribute to
the energy needs when there is a VO2
deficit. EPOC refers to excess post exercise
oxygen consumption
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Energy systems

• ATP-PC
• Limited intramuscular stores
• Very powerful

• Anaerobic Glycolysis
• End-products lactate, hydrogen ion

• Oxidative Phosphorylation
• Greatest capacity
• Least powerful
• VO2max

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ATP-PC
Anaerobic glycolysis
Oxidative phosphorylation
Relative energy potential of each energy system
8sec
2-3min
45sec
time
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VO2
Blood lactate concentration
OBLA
Exercise intensity
Anaerobic metabolism
Note that exercise duration is limited when the
intensity exceeds OBLA
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Steady state
VO2 deficit
EPOC
VO2
time
3.5ml/kg/min
Note anaerobic sources of energy contribute to
the energy needs when there is a VO2
deficit. EPOC refers to excess post exercise
oxygen consumption
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The EPOC comprises a fast component with the
restitution of high energy phosphagens (ATP CP)
and subsequent VO2 cost of lactate removal, work
of respiratory muscles, heart etc In the longer
term there is a raised metabolism associated with
increased circulating catecholamines, protein
synthesis and elevated body temperature.
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Fast run
Energy expenditure
Slow run
3.5ml.kg-1.min-1
Exercise duration
Note that the total energy expenditure for
running a kilometre is similar regardless of
running velocity However return to resting
metabolic rate differs with the intensity of
exercise (EPOC)
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Steady state
Heart rate
time
Heart rate response to exercise reflects the
cardiorespiratory stress or intensity of
exercise. Note that HR is influenced by the
ambient temperature, prior intense exercise,
ingestion of food and coffee.
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As a person increases their cardiorespiratory
fitness with regular exercise there is a
reduction in the sub-maximal steady state
exercise heart rate. (Note CO is unchanged)
unfit SV
Heart rate
fit SV
time
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Effect of increased PV heart size on the
submaximal exercise response ( SV)
sedentary
physically active
Heart rate
Ex intensity
Note that while the submax ex HR is reduced
the VO2 cost remains
unchanged
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unfit
fit
HR
Power
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Plateau in VO2
VO2
Increments in power
time
Note When VO2 does not increase with a further
increase in power then VO2max has been reached
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Cardiac output HR X stroke volume
VO2 l/min
Q or CO (cardiac output)
Estimate of Q 6 X VO2(l/min) 3
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SV increases during exercise up to an intensity
of 40 50 VO2max there are limited small
increases in SV after thistherefore increases in
CO are then a result of increases in HR.
40-50VO2max
Stroke volume
Exercise intensity (VO2max)
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• SV is affected by
• Chamber dimensions
• Myocardial mass
• State of peripheral vasculature
• Contractile state
• Response to inotropic stimulation
• (neural and hormonal)

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HRmax decreases with age Estimated HRmax 220
age (years) Therefore 20 year old person has an
estimated HRmax of 200 bpm compared with 140 bpm
for an 80 year old person. Thus CO max and
VO2max will decline with age as a consequence of
the age related decline in HRmax
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Fick equation VO2 CO X (a
vo2) (HR x SV) X
(arteriovenous O2difference)
CENTRAL versus PERIPHERAL
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• VO2max is the highest oxygen uptake attained by
  an individual(test criteria)
• Large muscle groups
• Dynamic exercise
• At sea level (diffusion gradients)
• treadmill exercise elicits 5-10 higher VO2

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• Criteria for the attainment of VO2max
• Plateau in VO2 despite an increase in power
• Estimated HR max attained
• RER greater than 1.3
• High (?) blood lactate concentration

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VO2 response to increasing ex intensity
(sedentary versus trained)
Physically active
VO2
sedentary
Exercise intensity
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• Males tend to have a higher VO2max than
  femalesWhy?
• More muscle mass (VO2 L.min-1)
• Less adipose tissue
• Higher Hb concentration
• - 15g/100ml versus 13.5g/100ml
• -1.34ml O2 / g Hb

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Cardiorespiratory fitness The VO2max of an
individual is the best indicator of
cardio-respiratory fitness Pulmonary
ventilation Gas exchange at the alveoli O2
carrying capacity of the blood Pumping capacity
of the heart Gas exchange at the muscle Capacity
of muscle to utilise O2
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CO is unchanged at rest and during sub-maximal
exercise following exercise training however
COmax is increased. Heart rate is lower at rest
and during sub-maximal following exercise
training no change in HRmax Changes in sub-max
HR and COmax are a direct result of a larger
stroke volume following exercise training and
reduced sympathetic stimulation
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Note During exercise there is a redistribution
of blood flow Blood flow to the kidneys, liver
and gut is reduced (vasoconstriction) while blood
flow to the exercising muscles is increased
(vasodilation) Venous return during exercise is
aided by the muscle pump action. When exercise
stops abruptly the muscle pump fails to maintain
venous return and the person experiences syncope
(orthostatic intolerance)
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Expired respiratory gas collection
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The work capacity of an individual is therefore
primarily determined by their VO2max BUT should
we consider this in terms of Litres/min OR
ml/kg/min?
Consider the following example
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• A little athlete may have a high VO2max of 70
  ml/kg/min but in absolute terms has a VO2max of
  2.24 L/min.(bodyweight 31.25kg)
• A coal miner has a VO2max of 40 ml/kg/min and
  weighs 90kg therefore he has a VO2max of 3.60
  L/min in absolute terms.
• Who will be able to better cope with undertaking
  a days work as a builders labourer or as a mail
  courier climbing stairs in an office tower block?

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Working at the same power output
VO2max
VO2
VO2 cost of work
Subject A
Subject B
Same work rate demands 40 VO2 max for Subject
A and 65 VO2max for Subject B
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Upper limits Intensity versus duration of
exercise
3K race VO2max
Marathon runner 85VO2max
Exercise intensity (VO2max)
8h manual labourer 30-35VO2max
Exercise duration
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RER VCO2 VO2
RER
Intensity
0.7 100 Fat 0.85 50 Fat 50 CHO 1.0
100 CHO
Note that the RER is influenced by nutritional
status ie. muscle glycogen stores
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The RER may exceed 1.0 during intense exercise as
additional CO2 is produced with the buffering of
lactate by bicarbonate. This excess CO2 is
therefore not the direct result of
metabolism. Note that the increased production
and build up of CO2 stimulates an increase in
VE Thus at this increased exercise intensity the
person begins to hyperventilate
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150w 100w

HR

50w
time
Estimated HRmax

150w
HR

100w

50w
Power
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Estimated HRmax
HR
Extrapolated from submax data points



Power
VO2
Predicted VO2max
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• Sources of error in predicting VO2max
• Estimated HRmax (error 10)
• HR may be influenced by ambient temperature,
  ingestion of coffee/food, URTI, sub-optimal cycle
  seat height/cadence etc.
• Large (overweight) person may be classified as
  fit unless the predicted VO2max is expressed
  relative to bodyweight

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Effect of temperature on HR
Hot day
Same power
HR
Cool day
time
HR response to arm v leg work
Arm work
HR
Leg work
Power
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• Note HRmax is usually attained before VO2max
• ie. VO2 can still increase despite no further
  increase in HR Why?
• can still increase extraction at the peripheral
  level despite no change in HR (or CO) may
  represent 5 error
• Therefore error may be as high as 15

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There are large differences in VO2max between
peopleto fully understand why, we need to
examine the oxygen conductance chain ie. the
process of uptake, transport and
utilisation. Limiting factors may be identified
as central or peripheral ie. concerned with
factors governing CO or the a-vo2 difference
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VE is not usually a limiting factor for the
attainment of VO2max in healthy individuals
VE
VE/VO2 30
VE/VO2 40
VO2
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VE is a significant limiting factor for the COPD
patient Patient with mitral stenosis will have
significantly reduced SV Patient with PVD will
have significant limitations in a-vo2 (femoral
artery occlusion) Patient with anaemia will have
reduced oxygen carrying capacity (low Hb Hct)