How muscles grow

Fitness - how to's

The human body is extremely complex and quite difficult for a non-scientist to understand. Yet a basic understanding of how the body functions will help you achieve your goal quicker and easier than training haphazardly.

If you are in training, your muscles are probably most important thing to you.

The change in the structure of your muscles bought about by exercise will have a significant effect on your physical appearance and wellbeing and this in turn will result in positive physiological changes.

So it is important you understand how muscles work, what you need to do to change them and the outcome of these changes.

There are three types of muscle:
Smooth Muscles
Also called nonstriated, is found in the internal organs such as the stomach and in the walls of blood vessels. They are what’s called involuntary muscles, in other words they are not under conscious control.
Cardiac Muscle
This is the muscle that forms the main part of the heart wall and again not under conscious control.
Skeletal Muscles
This is the largest group of muscles and these do work under conscious control. In other words these do what you tell them to do, when you tell them to do it.

For the most part, only the skeletal muscles benefit directly from exercise. I must quickly add that the heart muscle is strengthened by endurance exercise but this is secondary, the indirect result of increased demand on the circulatory system by the skeletal muscles. Therefore the skeletal muscles are the key to fitness.

There are more than 400 skeletal muscles and they range in size from the large gluteus maximus in your buttocks to the small muscles that control your eyelids.

Most skeletal muscles are attached to bones, thus the name. They do not join the bone directly. The muscles taper into bands or cables called tendons and it is the tendons that indirectly attached the muscle to the bone.

Most muscles are paired lying opposite sides of a bone. Muscles always pull (contract) to make a movement regardless of the direction of the movement that results. This can be best demonstrated with the arm. The bicep muscle that lies on the front of the upper arm, contracts, flexing the elbow and curling the arm upwards, basically using the bone as a lever to produce movement. This stretches the tricep muscle that lies along the rear of the same bone. The tricep muscle then contracts straightening the arm out stretching the bicep muscle.

So now we know how muscles make your joints move but what makes a muscle contract.

To know this you need to know what a muscle is made up of. Most people would see a muscle simply as a piece of meat, like a rump steak. However when you look at a muscle under a microscope it is a complex system of cells, fibres and membranes.

Now for the science bit. Muscle cells are in the form of fibres, cylindrical cells bound together by a membrane into bundles. To visualise a bundle think of a telephone cable with wires running inside it. Then inside these fibres are smaller cylinders called myofibrils. When chemically stimulated by the nervous system, these myofibrils contract, or shorten, how they contract can be seen under a microscope. The myofibrils consist of thin and thick myofilaments. These myofilaments contain proteins. The protein actin can be found in the thin myofilaments and the protein myosin in the thick ones. When you decide to move a muscle your brain sends an impulse to the appropriate fibres, which causes a chemical and mechanical link to occur between the actin and myosin filaments. The two filaments themselves do not shorten, they simply slide past one another, and the more they overlap the more contraction of the myofibrils, or the muscle, takes place.

You are now probably thinking that a muscle is a very complicated organ, but unfortunately it doesn’t stop there. The fibres in skeletal muscle come in two basic varieties. One kind is called fast twitch and the other slow twitch. As the name implies, the fast twitch fibre contracts almost twice as fast as slow twitch. Fast twitch fibres are larger of the two and much paler, almost white, in colour; slow twitch are dark reddish brown.

Each muscle contains a mix of the two. For example, a sprinters muscle will contain more fast twitch fibres, where as a marathon runner more of the slow twitch variety. However, the amount of fibres, are probably inherited and exercise does not seem to alter the number that much but it does increase the effectiveness of each type. This may be the reason why we are better at certain sports. The sport requires us to use the greater number of our inherited type of fibres. So the sport may actually choose us and not the other way round.

So now we know how a muscle works and what it is made up of but what effect does exercise have on them?

Jogging will increase the capacity of the slow twitch fibres, while sprinting training increases the fast twitch fibres but as weight training probably effects muscle growth more than any other exercise we will use this as the first example of what really happens when we put our muscles under stress.

When a muscle is subjected to an exercise such as weight training the probable outcome is an increase in the size of the whole muscle. Training with weights requires such strenuous contractions that the covering around the myofibrils stretches, opening up pores to let in more nutrients, particularly amino acids, the build blocks of protein and protein molecules form all kinds of muscle tissue. The increase supply of amino acids can then be used to make protein for additional actin and myosin filaments inside the myofibrils, expanding the size of the myofibrils. Some myofibrils may grow so much that they divide, creating entirely new ones. The result of this increase in bulk of the myofibrils is an increase in the fibres that the myofibrils form and finally the muscle.

Weight training also increases the number of blood vessels around the fibres and causes connective tissue throughout the muscle to thicken and increase the muscles diameter.

Weight training is an anaerobic (without oxygen) activity and the physical changes are mainly to the fast twitch fibres.

Aerobic (with oxygen) exercises that are so important to fitness and depend on the slow twitch fibres also effect the development of the muscles. The slow twitch muscles increase in size because of the demand they place on the circulatory system. Working muscles require oxygen rich blood to fuel them. As the muscle workload increases the capillaries can no longer deliver as much blood as the muscle needs. This brings about a localised shortage of oxygen and encourages new capillaries to grow into the oxygen short areas.

The need for oxygen imposed by endurance exercise does more than stimulate the growth of additional blood vessels it also improves the chemical handling of the oxygen carried by the blood. Myoglobin is the chemical that carries oxygen into the muscle cells. Aerobic exercise increases the concentration of myoglobin. With more myoglobin, more oxygen becomes available and more aerobic work can be done – endurance increases.

The benefits that exercise has on our muscles can only be described as outstanding. However to continue to reap these benefits you have to adopt what is called the Overload Principal.

The Overload Principal
To gain strength and endurance you must overload the muscle. This is probably the most important principal to understand in any sport or exercise and especially in weight training.

To overload a muscle means simply that you must stress the muscle in intensity or duration beyond the demands of the previous activity.

This is then followed by a rest period during which the muscle rebuilds with greater strength and endurance. The cells are programmed to rebuild stronger so they can handle greater stress next time. Note it is the rest period that the muscle builds not when you are exercising them so rest is as important as the exercise.

So that’s it. By following this simple principal you will be able to achieve your goals, whether they are modest, such as being able to run for a bus without pulling a muscle or as ambitious as winning the next Mr Universe – and I’ll bet now you will never take your muscles for granted again.

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