How Do Muscles Work?

Muscles | March 19, 2018 | Author: Naturopath

exercise, Muscles

How Do Muscles Work?

How do muscles move, and what do they actually need to work?

There are over 600 muscles in the human body, classified into three major groups:

Smooth muscles: These muscles around found all over the body. These are involuntary muscles – you can't consciously contract them, but they are constantly working. These types of muscles are  active wherever movement is necessary for basic body functions – e.g. in the digestive system, the bladder and behind the eyes.

Heart muscles: The myocardium makes up the thick muscular walls of the heart. Luckily heart muscles also contract and relax involuntarily, as it would take a lot of concentration to consciously keep the heart ticking 24/7.

Skeletal Muscles: These muscles are attached to bones and most people are able to move them voluntarily. This is what is generally referred to when people say “muscles” – quadriceps, biceps, etc.

Although they have very different functions, all muscles work in a similar way and require key nutrients for contraction, relaxation, recovery and growth.

How Muscles Contract

How Muscles ContractMuscle contraction works somewhat like rowing a boat across a lake. You first put the oars in the water and pull backwards to propel the boat forward. To keep moving, you must lift them out, place them forward and into the water, ready for the next stroke.

Muscles are made of two major protein filaments that run parallel to each other – myosin and actin.

 

Myosin filaments are quite thick and they initiate the force of the muscle contraction, similar to the oar in our metaphor. They have projections that branch outwards towards the thinner actin filaments. When contact occurs between the myosin projections and actin binding sites, a chemical charge occurs and the myosin projections (or “oars”) change shape. This change pushes the myosin “backwards”, like the back stroke of an oar, the myosin filament moves across the actin like a boat across water. The power of this movement in hundreds of filaments at once causes the muscle to contract. [9]

Just like rowing a boat, muscle contraction requires lots of energy:

Energy for Muscles

All muscles convert chemical energy into energy for movement. Chemical energy comes from the food we eat, which is converted into ATP – adenosine triphosphate – which is the type of kinetic energy used in muscle contraction. Muscles have very limited space to keep pre-made ATP, and quickly uses up its stores during movement. When a muscle contracts harder or faster, such as in exercise, it rapidly requires more ATP [10].

Here's how muscles create ATP:

1. Creatine phosphate – This is a highly concentrated compound that can be converted into a lot of ATP very rapidly. This rapid conversion also means that creatine phosphate is quickly used up – working muscles use up their storage of creatine phosphate within about 10 seconds.

            Used in exercise: Short-distance sprinters and weight lifters rely on creatine phosphate for short bursts that that only last 8 – 10 seconds.

For longer lasting energy, muscles need to use carbohydrates. Glycogen is a muscle storage form of glucose, which can be transformed into kinetic energy through two main reactions – one with and one without the help of oxygen.

2. Glycogen WITHOUT oxygen – It takes about 12 chemical reactions to convert glycogen into ATP – quite a long and tedious process requiring lots of nutrient cofactors. Through this reaction, muscle stores of glycogen can produce enough ATP to last about a minute and a half. A major negative is that creating ATP from glycogen without oxygen results in a big release of lactic acid – hello stitches, tiredness and soreness.

Used in exercise: Lasting a little over  1.5 minutes, this system is very active in short-distance events like a 100m swim or 200m sprint.

3. Aerobic respiration – Within two minutes of exercise, the heart and lungs are able to deliver oxygen to participate in aerobic respiration. This is a very long chemical process that breaks down glucose into ATP. Aerobic respiration takes longer than converting ATP from creatine phosphate or glycogen without oxygen, but it can last for hours. The glucose can come from multiple sources:

  • any remaining glucose in the muscle cells
  • glycogen stores in the liver
  • glucose from any foods broken down in the intestines
  • or a long process of converting fat reserves in the muscle

            Used in exercise: Aerobic respiration can provide energy for hours at a time, so it is used extensively in endurance and long-distance sports and exercise – or any time you're active for over 2 minutes or so! [9] [10]

Nutrition for Muscle Health   

Protein

Nutrition for Muscle Health   Muscle tissue is made of amino acids which bind together to form protein. Muscles don't use protein for energy unless in absolutely dire circumstances (e.g. starvation)  – this makes sense, because why would a body tissue use up the very thing it's made of unless it absolutely had to?

Protein is essential for muscle growth, recovery and maintenance.

A general rule is to consume 1g  of protein per kg of body weight per day. e.g. if you weigh 80kg, a healthy amount of protein is 80g per day. Remember that protein isn't just found in meat – brown rice, beans, tofu and nuts are healthy, rich sources of protein too! 

Glucose

As we explored above, muscles need ATP for energy and they can perform long-lasting contractions if they have access to various sources of glucose. Carbohydrates are the richest sources of glucose, but the body can make ATP from fat, too. Replenishing glucose stores after exercise is as important for muscle recovery and growth as getting enough protein [5].

Electrolytes

Certain minerals create an ionic charge when mixed with water. This charge is a key part of muscle contraction and recovery. Electrolytes are rapidly excreted during exercise through sweat and respiration, resulting in muscles that quickly get tired or cramp up. All electrolytes are needed in balance: sodium, potassium, magnesium, calcium and chloride.

Magnesium is an electrolyte that is also an essential cofactor in the chemical processes that create ATP. Plus, it's needed to shuttle lactic acid out of muscle cells  – if you suffer from post-exercise soreness and stiffness, try soaking in a bath with magnesium salts (i.e. epsom salts). [7]

Calcium is needed for the chemical reaction between the nervous system and muscles. Without adequate calcium, muscle contraction suffers, resulting in weakness, fatigue, and cramps [8]. Speak to a qualified nutritionist to ensure you are getting adequate calcium from your diet.

Supplements for Muscle Health 

Creatine

Creatine supplements are used to replenish creatine phosphate stores. When it comes to improving muscle performance, weight lifters and other people doing short-burst exercise may benefit the most [2]. In all active people, taking a creatine supplementation after exercise can also improve muscle growth and mass, and boost the water content in muscle cells, making them muscle bulk appear bigger [3]. CAUTION: Taking creatine can contribute to dehydration; be sure to drink plenty of water when supplementing with creatine.
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Branched Chain Amino Acids

Branched Chain Amino AcidsBCAAs are the amino acids that are most used to form muscle proteins – leucine, isoleucine and valine. They make up about 14% of the amino acids found in muscles. Supplementing with BCAAs can support muscle gain [1], though the benefits are most obvious in people who struggle to consume enough protein through their diet, such as vegans, people with Coeliac disease or any digestive issues, and the elderly.
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Zinc

Zinc is an essential mineral that can stabilise protein structures within muscle. It's also a rate-limiting cofactor in thousands of enzymatic reactions involved in muscle contraction and recovery – the more zinc available, the faster these reactions can occur. Taking 25mg of zinc per day can help to boost zinc stores that are [4]

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References

[1] Dudgeon, W. D., et al. (2016) In a single-blind, matched group design: branched-chain amino acid supplementation and resistance training maintains lean body mass during a caloric restricted diet. J Int Soc Sports Nutr. https://www.ncbi.nlm.nih.gov/pubmed/26733764

[2] Cooper, R., et al. (2012) Creatine supplementation with specific view to exercise/sports performance: an update. J Int Sports Nutr., 9, 33. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3407788/

[3] Atonio, J. & Ciccone, V. (2013) The effects of pre versus post workout supplementation of creatine monohydrate on body composition and strength. J Int Soc Sports Nutr., 10, 36. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3750511/

[4] Roohani, N., et al. (2013) Zinc and its importance for human health: An integrative review. J Res Med Sci., 18:2, 144 – 157. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3724376/

[5] Rose, A. J. & Richter, E. A. (2005) Skeletal muscle glucose uptake during exercise: how is it regulated? Physiology., 20, 260 – 270. https://www.ncbi.nlm.nih.gov/pubmed/16024514

[6] Richter, E. A. & Hargreaves, M. (2013) Exercise, GLUT4, and skeletal muscle glucose uptake. Physiol Rev., 93:3, 993 – 1017. https://www.ncbi.nlm.nih.gov/pubmed/23899560

[7] Gröber, U., et al. (2015) Magnesium in Prevention and Therapy. Nutrients., 7:9, 8199 – 8226. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4586582/

[8] Stein, R. B., et al. (1988) The kinetics relating calcium and force in skeletal muscle. Biophys J., 54:4, 705 – 717. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1330375/

[9] Herzog, W., et al. (2015) A new paradigm for muscle contraction. Front Physiol., 6, 174. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4461830/

[10] Baker, J. S., et al. (2010) Interaction among Skeletal Muscle Metabolic Energy Systems during Intense Exercise. J Nutr Metab., https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3005844/

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