Muscle blog series: Part 1: Introduction
This is the first article in the
series of muscle related topics. This article will give an introduction to
muscle and further topics in the future will cover things like delayed onset
muscle soreness, injury, flexibility etc. So stay tuned.
Definition of muscle:
A tissue composed of fibres
capable of contracting to effect bodily movement. A contractile organ
consisting of a special bundle of muscle tissue, which moves a particular bone,
part, or substance of the body.
How much muscle is there in our bodies?
Obviously this will vary but
generally muscles constitute to on average 40-50% of total body weight!
(Tortora & Grabowski, 2000)
There are different types of
muscle in the body, we will briefly talk about cardiac and smooth muscle just
so you know a little about them but as I am a physiotherapist I will
concentrate on skeletal muscle.
Cardiac muscle:
This is the muscle that forms the
heart. This muscle is striated and its action is involuntary. The heart
alternates between contraction and relaxation, which is controlled by an
internal pacemaker (autorhythmicity). Hormones and nerves adjust the rate the
heart beats at by slowing down or speeding up the internal pacemaker.
Smooth Muscle:
This is the muscle inside the
walls of hollow internal organs. It is found in most organs in the abdomen and
it is also found in blood vessels and airways. This muscle type is
non-striated, hence the name ‘smooth’. This muscle is also involuntary and just
like cardiac muscle it is influenced by hormones and nerves.
Skeletal muscle:
This muscle’s function is
primarily to move the bones of the body. But surprisingly not all do! Some
actually attach to other tissues and therefore move that rather than the
skeleton. A prime example of this is a muscle called articularis genus, which
only functions to pull the capsule of the knee joint out of the way of the
joint when the knee straightens so that the capsule doesn't get trapped by the
joint.
Skeletal muscle is striated and
it is primarily voluntary but not all of it and not all the time. For example
shivering when you get cold is not voluntary, muscle spasm when you have pain
is not voluntary and the above example of articularis genus or the diaphragm
are not voluntary either.
How many skeletal muscles are there in the human body?
640!! (However, some people have
more or less than this number)
What are the different functions of skeletal muscle?
Production of body movements
Stabilising body positions
Increasing venous return
Heat
What are the properties of skeletal muscle?
Electrical excitability
Contractility
Extensibility
Elasticity
Anatomy of Skeletal muscle:
Muscles are made up of thousands
of cells called fibres, connective tissue surrounds fibres and muscles, nerves
and blood vessels pass through, into and around muscle.
Connective tissue:
Superficial fascia: Separates
muscle from the skin (areolar connective tissue & adipose tissue)
Deep fascia: Surrounds muscle
groups
Epimysium: surrounds individual
muscles
Perimysium: surrounds groups of
between 10 - 100 muscle fibres, which are called fascicles
Endomysium: surrounds individual muscle
fibres
All connective tissue is
continuous throughout the body, there is no stopping and starting. The fibres
within the muscle continue and form the tendons to attach to bone and they also
continue on into the next structure along the chain.
Blood and nerve:
These are very abundant in
skeletal muscle
The muscle fibre itself:
The plasma membrane of the fibre
is called the sarcolemma, inside here is the sarcoplasm, which surrounds
myofibrils and it is these that are the contractile elements of the muscle. In
each myofibril is the filament, which is arranged into sacromeres. Each
sarcomere is made up of myosin and actin, which is where the sliding filament
theory of muscle contraction occurs.
Sliding filament theory:
The myosin heads walk along the
actin, which shorten the muscle, this is concentric muscle contraction. The
load on the muscle causes the myosin to be pulled back to the longer length,
this is eccentric contraction. If the load equals the contraction strength then
the fibre length stays the same, this is an isometric contraction.
Different fibre types:
Slow Oxidative: Smallest and
least powerful. Lots of mitochondria and blood vessels. This means they use
oxygen well and therefore are highly resistant to fatigue. Posture muscles are
full of these type and endurance athletes usually have a high distribution of
these.
Fast Oxidative-Glycolytic: medium
sized and moderately powerful. So are
somewhere between Slow Oxidative and Fast Glycolyyic, so athletes that need to
have a combination of speed and endurance will have more of these type.
Fast Glycolytic: Largest and most
powerful. Few blood vessels, contain lots of glycogen. They are anaerobic
mostly and are designed for short burst power but fatigue very quickly.
Sprinter and power lifter will have lots of these.
So although all this sounds
complicated, you can easily see why it is important to know as this will
influence your training and therefore performance.
If you use mostly fast glycolytic
fibres in your training then these will increase, making you more powerful but
easier to fatigue. This is great for a sprinter but would be bad news for the marathon
runner! The future blog articles in this series will show you how you can apply
this knowledge to your training to maximise performance and prevent injury.
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