3. Calorimetry & Oxygen Consumption

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En provenance du cours de University of Colorado Boulder

Science of Exercise

453 notes

University of Colorado Boulder

Science of Exercise

453 notes

Learners who complete Science of Exercise will have an improved physiological understanding of how your body responds to exercise, and will be able to identify behaviors, choices, and environments that impact your health and training. You will explore a number of significant adjustments required by your body in order to properly respond to the physical stress of exercise, including changes in carbohydrate, fat and protein metabolism, nutritional considerations, causes of muscle soreness & fatigue, and the effectiveness and dangers of performance enhancing drugs. Active learning assessments will challenge you to apply this new knowledge via nutrition logs, heart rate monitoring, calculations of your total daily caloric expenditure and body mass index (BMI). Finally, learners will examine the scientific evidence for the health benefits of exercise including the prevention and treatment of heart disease, diabetes, cancer, obesity (weight loss), depression, and dementia.

À partir de la leçon

The Energetics of Exercise

In this module you will learn about the various metabolic pathways (carbohydrates, fats and proteins) that are activated in order to supply the necessary energy required for the mechanical work of skeletal muscles during exercise. How these pathways are regulated, the methods for assessing the extent to which specific fuels are being utilized and the overall estimation of your metabolic rate will be addressed. Additionally, the importance of the chemical energy stored in ATP and its requirement for muscular work will be discussed.

1. Introduction to Exercise Science4:51

2. Principles in Exercise Physiology8:32

3. Calorimetry & Oxygen Consumption6:27

4. ATP & Muscular Work9:15

5. Carbohydrate Metabolism During Exercise9:21

6. Carbohydrate Metabolism Continued7:38

7. Fat Metabolism During Exercise7:58

8. Protein Metabolism During Exercise7:32

Rencontrer les enseignants

Robert Mazzeo, Ph.D.
Associate Professor
Department of Integrative Physiology

In this video, I will discuss the application and significance of calorimetry.

In Exercise Science, we are interested in quantifying or measuring

the amount of energy expended during a single bout of exercise.

This is useful for various reasons,

including-- determine the energy cost for a wide range of physical activities,

caloric expenditure for weight control,

and type of fuel or substrate being used by the muscles during exercise.

The technique of calorimetry is used to measure energy expenditure during exercise.

Calorimetry is defined as the measurement of heat production,

usually measured in units of calories.

As all metabolic processes eventually result in heat production,

such as a skeletal muscle during a contraction,

we can estimate an individual's metabolic rate by measuring the rate of heat production.

The actual measurement of heat production by the body is termed "Direct Calorimetry",

and can be used to estimate one's metabolic rate both at rest and during exercise.

Here is an example of a human calorimetry chamber.

The heat produced by the body during exercise

can be monitored by various thermal detecting devices.

These chambers are extremely expensive and thus,

are not very practical for clinicians,

health care providers, and researchers alike.

Indirect calorimetry is by far

the most common method for estimating one's metabolic rate,

specifically, by the measurement of oxygen consumption.

It is based on the observation that oxygen is consumed

by the body for energy production when your muscles are working.

A direct relationship exists between the amount of

oxygen consumed and the amount of heat produced.

So, by measuring the rate of oxygen consumption,

the indirect calorimetry, we can get

a very good estimate of an individual's metabolic rate.

The rate of oxygen consumption is indicated by V̇O2,

the V indicates the volume of oxygen and the dot over the V implies a rate,

in this case-- milliliters of oxygen consumed for a minute.

Notice the significant increase of oxygen consumption when we go from

a resting state to steady states of maximal exercise at a given intensity.

This represents the indirect calorimetry,

an increase in your metabolic rate compared to rest.

In order to measure an individual's maximal oxygen consumption,

which is the gold standard for assessing one's cardiovascular fitness,

the individual must complete a graded exercise test to exhaustion.

This is generally done on a treadmill or bicycle ergometer.

This test begins at a very easy workload.

Afterwards, the intensity is gradually increased every two to three

minutes until the individual fatigues and can go no further.

Oxygen consumption is measured at the end of each stage and plotted against workload.

As can be seen,

oxygen consumption increases with increase in grade,

indicating a greater metabolic rate required for the extra work.

Notice that in going from grade 5 to grade 6,

oxygen consumption does not significantly increase despite the increased workload,

indicating the individual has reached his or her maximum rate

of oxygen consumption or V̇O2 max.

As shown here, V̇O2 increases linearly with

increasing workload until V̇O2 max is achieved.

A hallmark training adaptation associated with

regular endurance training is an increase in one's V̇O2 max.

The reason for this increase relates to improvements in oxygen delivery,

thus cardiovascular adaptations, as well as

improvements in muscle mitochondrial oxygen utilization.

We will discuss these training adaptations more thoroughly in a later module.

Endurance or aerobic activities that recruit a large muscle mass over

an extended period of time generally produce

athletes with the highest values for V̇O2 max.

As such, cross-country skiers and distance runners

typically have the highest reported values for V̇O2 max.

In addition to measuring oxygen consumption,

a second feature of indirect calorimetry is that it allows us

to measure the amount or volume of carbon dioxide produced by the body.

This knowledge, coupled with the value for oxygen consumption,

allows us to calculate the respiratory exchange ratio shown here.

This ratio is simply the volume of carbon dioxide

produced divided by the volume of oxygen consumed.

This ratio is very useful as it provides valuable information

on the type of fuel or substrate being used by the muscles during exercise.

For example, if you are burning pure fat your respiratory exchange ratio will be 0.70.

If you are burning pure carbohydrate your respiratory exchange ratio will be 1.0.

This is valuable information for clinicians,

researchers, and athletes alike.

Here's a commonly used fat,

the 16 carbon free fatty acid palmitate,

used by muscles during exercise for fuel.

Notice that the respiratory exchange ratio for

its complete oxidation to carbon dioxide and water is 0.70.

With the complete oxidation of glucose,

the primary carbohydrate used by muscles during exercise,

the respiratory exchange ratio is 1.0.

Armed with this information researchers have

determined that carbohydrates are used to a greater extent than

fats for sprinting and

high power activities while the use of fats is preferred for distance athletes.

This will be discussed in detail later in this module.

Indirect calorimetry can be used to estimate an individual's metabolic rate,

both at rest and during exercise.

Endurance training will result in an increase in maximal oxygen consumption.

Respiratory exchange ratio can provide an indication

of the type of fuel used by the muscles during exercise.

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