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How Muscles Work

Train Smart: Understand How Muscles Work

Understanding how muscles work will help you target specific types of training to achieve your fitness goals. 

There are different types of muscles for performing slow and fast movements.

Also, a different kind of muscle movement results in a different chemical process.

Both the muscle type and chemical reaction used to produce power will depend on whether your movement requires a slow contraction, a short burst of power, longer sustained movement of low intensity, or high-intensity contraction for longer periods of time.

Fast-Twitch and Slow-Twitch Muscles

How Muscles WorkFast Twitch Muscles
The purpose of this type of muscle is to provide rapid movement for short periods of time.

They use glycogen, a type of glucose stored in the liver and muscles. Our body uses carbohydrates to synthesize glycogen.

Furthermore, fast-twitch muscles provide you with strength and speed.

Slow Twitch Muscles
As their name indicates, these fibers have a slower contraction time. Unlike fast-twitch muscles, this type of muscle uses oxygen for power.

The large muscles found in the legs, thigh, trunk, back, and hips are all slow-twitch.

Adenosine Triphosphate (ATP) is the main source of energy for all muscle contractions. ATP is produced in the body through several chemical reactions.

How ATP is Created in the Body

The Strength Enzyme System
When your muscles need additional strength, ATP is created quickly from the following chemical reaction. The enzyme creatine kinase mediates ATP production from the high energy molecule Creatine Phosphate (CP) by an anaerobic reaction.

The Burst Power Enzyme System
It takes less than two minutes to deplete the enzymes needed for this reaction, called Anaerobic Glycolysis. It uses glucose without oxygen.

The Endurance Enzyme System
Aerobic muscles can use ATP from three sources: carbohydrates, fats, and amino acid proteins.

Among the three, the most efficient in metabolizing are carbohydrates. Thus, carbohydrates are used first. If carbohydrates are not available, your body will then metabolize fat and amino acid proteins.

All three of these reactions are called Aerobic Glycolysis because they use glucose and oxygen:

  1. Carbohydrate Metabolism: Glucose + O2 -> 36 ATP + CO2 + H2O
  2. Fat Metabolism: Fatty Acid + O2 -> 130 ATP + C2 + H2O
  3. Amino Acid Protein Metabolism: Amino Acids + O2 -> 15 ATP + CO2 + H2O

The Breakdown

  • Your body stores glucose and fatty acids for these reactions.
  • Oxygen is provided continuously through breathing.
  • You have enough glycogen stored in your body for about two hours of intense activity.
  • You can extend this time by aerobic physical conditioning and following a high carbohydrate diet.
  • After your stored glycogen is used up, your body obtains its energy from fatty acid metabolism and amino acid protein metabolism.
  • However, these reactions are not efficient, which consequently cause your strength and endurance to drop drastically.

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