Calorimeter – Insulated airtight chamber. The walls of which contains copper tubing through which water is passed. In the chamber the heat produced by the body radiates to the walls and warms the water. The water temperature change is recorded, as are temperature changes of the air entering and leaving the chamber.
Heat is not measured directly. Energy expenditure is calculated form the respiratory exchange of O2 and CO2.
16 C + 16 O2 = 16 CO232 H + 8 O2 = 16 H2O16/23 = 0.7
Exercise physiology 5
Basic unit of heat is the Calorie.
This expresses the quantity of heat necessary to
raise the temperature of 1kg (1 L) of water by 1°C.
Measurement of heat actually produced by the body
which is confined in a sealed chamber or
Slow to generate results
Cannot follow rapid
changes in energy
Motor driven ergometers
give off heat as well
Not all heat is liberated
from the body
Sweat affects body
temperature and mass
Measures heat directly
To date it is easier and less expensive to measure
energy expenditure by assessing the exchange of
oxygen and carbon dioxide that occurs during
Hence, the method estimating total body energy
expenditure (indirect calorimetry) is more
Closed circuit and open circuit spirometry
represent the two methods of indirect calorimetry.
Closed Circuit Spirometry
This is currently used in hospitals and research
laboratories to estimate resting energy expenditure.
With this system the subject breathes 100% oxygen
from a prefilled container spirometer.
The spirometer acts as the closed system as the
individual rebreathes only the gas in the spirometer,
and no outside air enters the system.
A canister with soda lime (potassium hydroxide)
placed in the breathing circuit absorbs the persons
exhaled carbon dioxide.
A drum attached to the spirometer revolves at a
known speed and records the difference between
the initial and final volumes of oxygen in the
This system is not suitable for use during exercise
where the subject movement is required and large
volumes of air are exchanged.
Open Circuit Spirometry
Here a subject inhales ambient air with a constant
Changes in oxygen and carbon dioxide percentages
in expired air compared with inspired ambient air
indirectly reflects the ongoing process of energy
The difference between inspired and expired air
dictates how much O2 is being taken up and how
much CO2 is being produced.
The body’s limited O2 storage, allows for an
assumption that the amount of O2 taken up at the
lungs accurately reflects the body’s use of O2.
This technique is limited to steady state activities
lasting for approx. 1 min or longer, as energy
production must be almost completely oxidative.
Anaerobic energy will not allow for respiratory gas
measurements to reflect all metabolic processes.
Three common open circuit, indirect calorimetric
procedures measure oxygen uptake during physical
The simplest and oldest methods of indirect
calorimetry are probably the most accurate
Consumption and Carbon
Equipment used for indirect calorimetry utilizes the
volume of oxygen consumed (VO2) and the volume
of carbon dioxide produced (VCO2).
Generally the values are represented as oxygen
consumed per minute and carbon dioxide produced
VO2 = volume of O2 inspired – volume of O2
Volume of O2 inspired = Volume of air inspired X
fraction of that air that is composed of O2.
Volume of O2 expired = Volume of air expired X
fraction of the air that is composed of O2.
Same for CO2.
Calculation of VO2 and VCO2 requires:
Volume of air inspired (VI)
Volume of air expired (VE)
Fraction of O2 in the inspired air (FIO2)
Fraction of CO2 in the inspired air (FICO2)
Fraction of the O2 in the expired air (FEO2)
Fraction of the CO2 in the expired air (FECO2)
Equation for VO2
VO2 = (VI X FIO2) – (VE X FEO2)
Equation for VCO2 production
VCO2 = (VE X FECO2) – (VI X FICO2)
For many years scientists have attempted to
simplify the actual calculation of O2 consumption
and CO2 production.
Several of the measurements needed in the equation
are known and do not change.
The gas concentration of the three gases that make
up inspired air are known:
79.03% N (plus small quantity of inert gases)
To estimate the amount of energy used by the body, it is
necessary to know the type of food substrate being
The carbon and oxygen contents in these substrates vary
greatly, hence the amount of oxygen used during
metabolism depends on the type of fuel being oxidized.
The ratio between the amount of O2 consumed and CO2
released is termed respiratory exchange ratio (RER).
RER = VCO2 / VO2
Generally, the amount of oxygen needed to
completely oxidize a molecule of carbohydrate or
fat is proportional to the amount of carbon in that
6 O2 + C6H12O6 6CO2 + 6H2O + 38 ATP
By evaluating how much CO2 released compared with
the amount of O2 consumed.. RER = 1.0
In contrast to metabolizing free fatty acids where
there is considerably more carbon and hydrogen but
less oxygen than glucose.
For eg oxidation of palmitic acid:
23 O2 + C16H32O2 16CO2 + 16H2O + 129 ATP
Combustion of fat molecule requires significantly
more oxygen than combustion of carbohydrate
During carbohydrate oxidation, approx. 6.3
molecules of ATP are produced for each molecule of
O2 used (38 ATP per 6 O2).
Compared with 5.6 molecules of ATP per molecule
of O2 during palmitic acid metabolism (129 ATP per
Although fat provides more energy than
carbohydrate, more oxygen is needed to oxidize fat
This means that the RER for fat is lower; for palmitic
RER = VCO2/ VO2 = 16 / 23 = 0.70
Caloric Equivalence of the Respiratory
Exchange Ratio (RER) and % kcal from
Carbohydrate and Fats
Energy % kcal
RER Kcal/L O2 Carbohydrates Fats
0.71 4.69 0 100
0.75 4.74 16 84
0.80 4.80 33 67
0.85 4.86 51 49
0.90 4.92 68 32
0.95 4.99 84 16
1.00 5.05 100 0
Once the RER value is determined from the
calculated respiratory gas volume. The value can be
compared with the table to determine the food
mixture being oxidized.
Limitations of Indirect
Assumption that the body’s O2 content remains
constant and that CO2 exchange in the lung is
proportional to its release from the cells.
CO2 exchange is less constant, and the amount
released in the lungs may not represent that being
produced in the tissues.
So calculations of carbohydrate and fat used based
on gas measurements appear to be valid only at rest
and during steady state exercise.
Use of RER can also lead to inaccuracies.
Nil calculations of the body’s protein use from the
Recent evidence suggests that exercises lasting for
several hours, protein may contribute up to 5% of the
total energy expended under certain circumstance.
Isotopic Measurements of
The use of isotopes has expanded the ability to
investigate energy metabolism.
Isotopes are elements with an atypical atomic weight.
They are either radioactive or nonradioactive.
These isotopes are used as tracers, selectively followed in
Tracer techniques involve infusing isotopes into an
individual and then following their distribution and
Isotope turnover is relatively slow, energy
metabolism must be measured over weeks.
Thus, this method is not well suited for
measurement of acute exercise metabolism.
However, its accuracy (>98%) and low risk make it
well suited for determining day to day energy
The VO2max represents the greatest amount of
oxygen a person can use to produce ATP aerobically
on a per minute basis.
This usually occurs with high intensity, endurance
Athletes who compete in endurance sports records
the highest VO2max.
However, this does not mean that only VO2max
determines endurance exercise capacity.
VO2max represents a fundamental measure in exercise
physiology and serves as a standard to compare
performance estimates of aerobic capacity and
Tests for VO2max use exercise tasks that activate large
muscle groups with sufficient intensity and duration to
engage maximal aerobic energy transfers.
Research has been directed towards:
Developments and standardization of tests for VO2max
Establishments of norms related to age, gender, state of
training, and body composition.
Tests of Aerobic Power
There are different standardized tests to measure VO2max.
Such tests remains independent of:
These tests may require a continuous 3 – 5 minute
“supermaximal” effort, but it usually consists of
increments in exercise intensity (graded exercise test /
GXT) until the subject stops.
Two types of VO2max tests are typically used:
Continuous test : no rest among exercise increments.
Discontinuous test: several minutes of rest between
Commonly used treadmill protocols:
Features common to each test include manipulation
of exercise duration and treadmill speed and grade.
Factors Affecting Maximal
Heart Rate Predictions of VO2max
Tests make use of the essentially linear relationship
between heart rate and oxygen uptake for various
intensities of light to moderately heavy exercise.
The slope of the line reflects the individuals aerobic
VO2max is estimated by drawing a best fit straight line
through several submaximum points that relate to
heart rate and oxygen uptake (or exercise intensity)
and then extrapolating to an assumed maximum heart
rate for the person’s age.
All predictions involves error.
The error is referred to as the standard error of
estimate (SEE) and is computed from the original
equation that generated the prediction.