8. Protein Metabolism During Exercise

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Science of Exercise

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University of Colorado Boulder

Science of Exercise

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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

We will conclude module one by discussing the key concepts of protein metabolism.

As you will see, proteins play a small yet

significant role in muscle energetics during exercise.

The main contribution of proteins come after an exercise bout and

involves the early stages of training adaptations.

This may include the synthesis of key structural, enzymatic, and

muscular proteins depending upon the training stimulus.

Proteins are composed of their amino acid building blocks.

Essential amino acids cannot be made by the body,

thus they must come from dietary sources.

Nonessential amino acids can be synthesized in the body so

no dietary sources required.

In order to use proteins for

fuel, they must be broken down into their amino acid form.

Shown here is the essential amino acid pool.

Notice that amino acids from this pool, can be used to synthesize body proteins.

And body proteins that are degraded can release their amino acids

building blocks into this central pool.

Importantly, amino acids from this central pool can be converted to carbohydrate and

fat, thereby serving as a potential fuel source for the exercising muscles.

As nitrogen is a fundamental component for all amino acids, researchers and

clinicians typically measure nitrogen balance to determine an individual's

dietary protein needs, as well as their general whole body protein metabolism.

Simply stated, the amount of nitrogen

entering the body through the diet is compared to the amount being excreted.

If an individual nitrogen input is equal to their nitrogen output,

there said to be in nitrogen balance indicating that they do not need to

alter their dietary protein intake.

Most healthy adults with an adequate diet will be in nitrogen balance.

You'll be in positive nitrogen balance if your dietary intake of nitrogen

exceeds that of output.

This will suggest that the body is holding on to more nitrogen for

the synthesis of body proteins.

Children will be in positive nitrogen balance as the variety of proteins

must be synthesized for growth and development.

An individual can also enter into nitrogen balance

when they engage in intense strength training coupled with a high protein diet.

Body builders taking anabolic steroids magnify this response.

Negative nitrogen balance occurs when output exceeds input.

This would suggest that the body is breaking down or

degrading proteins for fuel.

This can happen during starvation or illness and even with the best aging.

The recommended daily allowance for sedentary adult men and

women is 0.8 grams of protein per kilogram of body weight per day.

As shown here the protein requirement will be greater

than intense in endurance training as well as during heavy strength training.

These individuals should pay close attention to their protein intake

to ensure their remain in nitrogen balance.

Let's look at how a single bout of exercise affects protein metabolism.

Muscle protein synthesis actually decreases during a bout of

aerobic exercise.

Remember, ATP utilizing pathways such protein synthesis are inhibited

as the energy charge drops during exercise to preserve ATP for mechanical work.

However, notice the very significant increase in the rate of protein synthesis

during the period immediately following exercise.

This is a crucial time for

the initiation of training adaptations as will be discussed shortly.

Proteins can actually be broken down or degraded during a single bout of exercise

with their resulting amino acids being used for fuel.

The carbon skeletons of certain amino acids can directly be used for

ATP production in the mitochondria.

The extent to which protein are degraded will be dependent on exercise

intensity and duration as well as the availability of carbohydrates.

When carbohydrates stores are low there will be greater dependence on protein

for fuel.

All things considered,

proteins can contribute approximately five to 15% of the fuel required for exercise.

Now, let's examine the basic adaptations related to protein metabolism

associated with both endurance and strength training.

We will begin by looking at the protein response when previously sedentary

individuals initiate a regular exercise program.

Notice that at the onset, an individual dependent upon the exercise intensity of

training, can enter into negative nitrogen balance, indicating that

during this period, protein breakdown exceeds that for synthesis.

Such an individual would benefit by increasing their protein intake

above the recommended daily allowance.

We will thoroughly discuss the mechanisms responsible for both endurance and

strength training adaptations in module three.

For now it is important to realize that individuals involved in

heavy endurance training will demonstrate adaptations specifically

related to mitochondrial protein metabolism.

This includes increases in mitochondrial number, size and

related enzymes, all requiring an increase in protein synthesis.

With intense strength or resistance training,

the muscle can increase in size, known as hypertrophy.

This increase in muscle mass can only occur with an elevation

in the rates of muscle protein synthesis.

This emphasizes the need for such individuals to have a dietary protein

intake significantly above that for the recommended daily allowance.

Intense strength training, when coupled with the use of anabolic steroids,

will result in even greater gains in muscle mass and thus the need for

increased dietary protein intake.

Finally, as a reminder, the rates of protein synthesis

are immediately elevated after a single bout of exercise.

For strength training, ingestion of proteins and

amino acids during this approximately one hour window will further stimulate and

enhance muscle protein synthesis.

In summary, athletes as well as individuals

initiating a training program need to be sure to maintain nitrogen balance.

Protein degradation increases during exercise and

certain amino acids can be used directly as fuel for ATP production.

Muscle protein synthesis decreases during exercise but increases during recovery.

Training adaptations related to protein metabolism are task specific and

occur primarily post exercise and

may require an adjustment in the recommended daily allowance.

This concludes module one.

In module two, I will discuss how many key physiological systems respond and

adapt to exercise.

I hope to see you there.

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