How to calculate exercise energy expenditure – SECOND PART –

In the exercise physiology’s field, energy can be presented using several ways, such as absolute oxygen consuption (L*min or ml*min), Relative Oxygen Consumption (ml*Kg*min), Metabolic Equivalent (MET), and Kilocalories.

Oxygen consumption is the rate at which oxygen is used by the body and it can be expressed in both absolute and relative oxygen consumption.

Absolute Oxygen Consumption is the raw volume of oxygen consumed by the body, whereas relative oxygen consumption is the volume of oxygen consumed relative to the body weight and can serve as a useful measure of fitness between individuals.

METs present the energy cost of the exercise in a simple format that can be understand by the general population to gauge exercise intensity, 1 MET is equal to the relative oxygen consumption at rest, which is approximately 3,5 ml*kg*min, so, if an individual is working at 7 MET, it’s completing approximately 7 times the amount of work and using 7 times the amount of energy of that at rest.

METs can be used to calculate energy expenditure over time:

Kcal*min= (MET * Body mass in Kg * 3,5)/200

Now that we know all the unit of measure used to assess exercise’s energy expenditure we can understand how to calculate it.

The only gold standard technique used to assess energy consumption during the exercise is the open circuit spirometry, this tool is not accessible or feasible in all applications, that’s Why the ACSM provided metabolic formulas to allow trainers an alternative method of energy cost estimation for popular modes of physical activity. These formulas calculate gross energy expenditure, which refers to the sum of energy used at rest and during exercise, that is different to the net energy expenditure, which is the energy cost of exercise that exceed the energy required to support the body at rest:

Net Vo2= gross Vo2 – Resting Vo2

Thus, the energy costs calculated from the metabolic formulas will represent the amount of energy required to complete the exercise task, including the energy required to support resting conditions.

Once got the energy consumption of a specific activity, a simple math operation will allow us to calculate the energy consumption in Kcal.

The follows table represent the ACSM Metabolic Formulas:

S is the speed expressed in meters* min.

G is the grade in percentage expressed in decimal format (10% = 0,10).

Work Rate is the resistance of the cycloergometer (expressed in Kg) * distance per revolution of flywheel * pedal frequency per minute (we have to take into account that distance per revolution is 6 meters for Monark leg ergometer, 3 meters for the Tunturi and BodyGuard ergometers, and 2,4 meters for Monark arm ergometer).

F is stepping rate

H is the step’s height expressed in meters

An example will help us to understand how to use these formulas:

Let’s come back with our 40 years old man with a body mass of 100 kg, let’s presume that he’s biking on a monark cycle ergometer for 1 hour of time on a frequency of 100 rpm, he’s caloric consumption will be the fallows:

Vo2max= (1,8*work rate/ body mass ) + 3,5 +3,5

(1,8 * 100*6/100) + 7

10,8 + 7 = 17,8 ml*kg*min

We know that this man is consuming 17,8 ml*kg*min, all we have to do is convert it in Kcal; 17,8 is the relative oxygen consumption and we have to convert it in absolute oxygen consumption, to do this, we have to multiply relative oxygen consumption per body mass:

Absolute Vo2Max: 17,8*100= 1780 ml*min

1780/1000= 1,78 L*min (we have to convert milliliters in liters to get Kcal)

1,78 * 5 = 8,9 Kcal*min

Considering that this man is biking per 1 hour (60 minutes), all we have to do is multiply 8,9 x 60, so, the energy consumption will be 534 kcal in one hour of work.

Heart rate monitor can be used to estimate energy consumption; a study reported on journal of sport science during the 2005 by Keytel, L.R. ; Goedecke, J.H. ; Noakes, T.D. ; Hiiloskorpi, H. ; Laukkanen, R. ; van der Merwe, L. ; Lambert, E.V talked about how to do that.

The aims of this study were to quantify the effects of factors such as mode of exercise, body composition and training on the relationship between heart rate and physical activity energy expenditure (measured in kJ x [min.sup.-1]) and to develop prediction equations for energy expenditure from heart rate.

Two equations were developed to predict energy expenditure (EE), a first one which contain a measure of fitness and a second one without it.

1. EE= -59.3954 + gender x (-36.3781 + 0.271 x age + 0.394 x weight + 0.404 V[O.sub.2max] + 0.634x heart rate) + (1 – gender) x (0.274 x age + 0.103x weight + 0.380x V[O.sub.2max] + 0.450 x heart rate)
2. EE= gender x (-55.0969 + 0.6309 x heart rate + 0.1988 x weight + 0.2017 x age) + (1 – gender) x (-20.4022 + 0.4472 x heartrate – 0.1263 x weight + 0.074 x age)

Where gender is 1 for Males and 0 for Females.

In conclusion we can say that there are a lot of useful tools which allow as to estimate energy consumption during the exercise, all we have to do it’s make practice over and over again, keeping us upgrade and try to make the difference in our job with ethic e professionalism, helping clients accomplish their goals.

About the author:
Dott. Mucedola Francesco

ACSM Certified Exercise Physiologist

Training Lab Certified Personal Trainer

M.Sc. Adapted Physical Activity

B.Sc. in Sport and Exercise Science

Bibliography

• Prediction of energy expenditure from heart rate monitoring during submaximal exercise Article in Journal of Sports Sciences · April 2005
• Objective Monitorin of Physical Activity Using Motion Sensor and Heart Rate
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Black, A E. International Journal of Obesity and Related Disorders; Hampshire24.9 (Sep 2000): 1119-1130

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Firstbeat Technologies Ltd.

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Mark D Muffin, Sachiko TSt Jeor, Lisa A Hill, Barbara J Scott, Sandra A Daugherty, and Young 0 Koh

• Skeletal Muscle Metabolism Is a Major Determinant of Resting Energy Expenditure
• The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass.
• An Energy Expenditure Estimation Method Based on Heart Rate Measurement
• ACSM Resources for the exercise Physiologist