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Muscles from the Inside Out

By Cindy | February 21, 2008

The body consists of thousands of cells constantly in motion. Remember biology class and the discussion of cells? Are your eyes already glossing over? Well, the cells of muscles are going through all the chemical experiences lost to high school memories and I do not want to bore you with all the scientific jargon. What do you need to know about the muscles in relation to strength training? A cross section of the muscle fibers that bundle together to shape your muscles doesn’t begin to show you the things that are happening at a microscopic level. I’ve narrowed the biology class to briefly outline four main points:

1. What are the abilities of skeletal muscle?
2. How to achieve muscular strength.
3. Components of the Muscle
4. Definitions and Energy Systems

What are the Abilities of Skeletal Muscle?

The body has three types of muscles: skeletal, smooth and cardiac. The smooth and cardiac muscles deal with the cardiovascular system. When muscles are discussed in strength training, it is skeletal muscle, connected to the bones, that is being discussed. There are a few key points that help explain the concept of strength training:

• Voluntary Control: Muscles only move when nerve impulses are activated.
• Muscles contract in one direction. Muscles work against each other and require an opposing partner.
• The All-Or-None Response of a muscle fiber. Individual fibers within the muscle contract completely upon exceeding a certain threshold, or it will not contract at all. When you move your arm, a certain number of muscle fibers will be called upon to contract, those fibers exert a complete force. Research shows that approximately 40% of muscle fibers are recruited in sedentary individual for a given muscle group for one maximal effort.¹
• All-Or-None Response is not the complete muscle! The muscle for a particular part of the body is stimulated based on the number of contracting muscle fibers within the muscle. If your body is only recruiting a few fibers to complete a movement, then the entire muscle is contracted weakly. The number of neurons sent to the muscle can stimulate up to 100 muscle fibers. As strength training is applied, the body signals more neurons to muscles as well as stimulates more muscle fibers to become more efficient.

How are Strength Gains Achieved

The body adapts to the muscles that are used. It will provide the energy to the fibers that are called upon to get the job done. No more, no less. In order to achieve strength gains, the body must be overloaded.

• Muscle fiber Recruitment. An increased in the use of muscle fibers creates a chemical change within the cells to use energy and create movement.
• Increased size of muscle fibers, called hypertrophy. Hypertrophy is much more prevalent in men than women due to testosterone levels.

The Components of the Muscle

A Muscle Fiber is a muscle cell.

Muscles are composed of muscle fiber bundles.

There are four layers of connective tissue surrounding a muscle. Endomysium for individual fibers, perimysium wraps bundles of fibers (fasicles), epimysium and fascia enclose the entire muscle. Fat will collect in the fascia of obese individuals. The belly of the muscle, known as the Gaster, contains the muscle fibers. The rest of the layers come together to connect the muscle to the bone by forming tendons at the ends.

Each fiber can be broken down into smaller units of filaments, called myofibrils, and then into even smaller units called sacromeres. What does this mean? Too many scientific words and processes to explain here, but your muscles are complex and they need lots of different proteins, fluids, and “other” stuff to work properly. Your body is amazing!!!

Other Facts:

1. Muscle fibers are thinner than a human hair and can support up to 1,000 times it’s own weight.

2. Muscles are efficient. They normally use about 35-50% of their potential energy.

3. Muscle soreness is a result of microscopic trauma of tissue and not due to lactic acid.

Definitions and Energy Systems

In order to understand the chemistry behind the cell functions of a muscle, here are a few important definitions from Merriam-Webster Dictionary:

Metabolism: the chemical changes in living cells by which energy is provided for vital processes and activities and new material is assimilated.

Adenosine Triphosphate: energy for many biochemical cellular processes by undergoing enzymatic hydrolysis

Lactic Acid: present in muscle tissue as a product of anaerobic glycolysis. The cause of muscle fatigue because oxygen is depleted and interferes with muscle contraction.

Glycolysis: the enzymatic breakdown of a carbohydrate (as glucose) by way of phosphate derivatives with the production of pyruvic or lactic acid and energy stored in high-energy phosphate bonds of ATP.

Krebs Cycle: a sequence of reactions in the living organism in which oxidation of acetic acid or acetyl equivalent provides energy for storage in phosphate bonds (as in ATP)

Muscle Tone, tonus: A condition in which a muscle is kept partially contracted over a long period of time. It is produced when one set of fibers, then another set, is briefly stimulated so that some part of the muscle is always contracted, although most of the muscle remains relaxed. For example, normal posture in the presence of gravity is achieved by tonus. Exercising increases the tonus of muscles used.¹

The body functions through 3 energy systems. Each system is dependent upon intensity. The systems work in some sort of combination. All cells in the body require adenosine triphosphate, ATP. ATP is the energy needed to contract a muscle fiber. Calcium, sodium and potassium are also needed. With oxygen, the muscle maintains it’s contraction and ability to move.

1. ATP-PC System is where energy is already stored in the muscle. The system works for up to ten seconds and is the immediate tap for energy.

2. Anaerobic Glycolysis is where the breakdown of glucose occurs in the absence of oxygen. The chemistry is complex and this is when lactic acid begins to build up. Considered high intensity exercises, this system lasts between 10 and 90 seconds. Lactic acid is believed to be the limiting factor in muscle fatigue because the demand for ATP is greater than supply and it interferes with the filament connections necessary for muscle contraction.

3. Aerobic System is where both glucose and fatty acids begin to break down with the presence of oxygen. For activities longer than two minutes, the aerobic system will predominate while activities are continuous.

Body chemistry is always working to become more efficient. Overall, the body wants to do the work with as little resistance as possible. It finds the short cuts. By stimulating different muscle fibers, the body focuses on providing the necessary energy to efficiently move. Through overload and muscle stimulation, the body taps into energy stores (i.e. fat tissues) to accomodate the needed energy depletions. To rebuild the muscles, the body will continue to work to restore the muscles to greater strength (increasing resting metabolism) to prepare for future stresses. For more information on the structure of muscles, click here.

References:
¹Alcamo, Edward and Krumhardt, Barbara. Anatomy and Physiology: The Easy Way. Barrons. Hauppauge, NY, 2004. 151-160. The majority of the information discussing anatomy is summarized from this reference.
²Summary of Energy Systems acquired through my training and course material provided by Cooper Institute.
Picture is from Ivy Rose Holistic.

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Topics: Fitness Knowledge |