Muscular System

Muscular system

This system is mainly concerned with producing movement through muscle contraction. This section explores the different types of muscles in our body and their involvement in sporting activities.

Muscle types

There are three types of muscle in the body:

SMOOTH MUSCLE- Found in the internal organs and blood vessels – this is involuntary
CARDIAC MUSCLE- Found only in the heart – this is involuntary
SKELETAL MUSCLE- Attached to the skeleton – this is voluntary

Involuntary muscles are not under our conscious control which means we can’t make them contract when we think about it.

Voluntary muscles are under our conscious control so we can move these muscles when we want to.

Muscle Fibre Types

There are three two different types of skeletal muscles:

Slow twitch
Fast twitch

Long distance cyclists need a high percentage of type I fibres so that their muscles can work for the duration of a race without getting tired. These muscles are red in colour because of the amount of capillaries that transport the oxygenated blood to the working muscles.

Sprinters need a high percentage of type II fibres which allow their muscles to contract very quickly. Fast muscle contractions give runners power and enable them to maintain a high speed over a 100 m distance. However, this type of muscle tires very quickly, meaning sprinters are not able to run at this speed for very long.

identifying the muscles

Muscles and movement

Muscles cause movement by contracting across joints. Muscles are attached to the skeleton by tendons in two places:

the origin
the insertion

The origin is the end of a muscle which is attached to a fixed bone. The insertion is the other end of the muscle that is attached to the bone which moves.

Muscular contractions:

Muscles contract in different ways to produce a range of movements:

Isotonic contraction
this involves the muscle producing tension and controlling the speed of the muscular contraction. This movement can be a concentric or eccentric muscular contraction.
Concentric contraction
this involves the muscle shortening. The origin and insertion of the muscle move closer together and the muscle becomes fatter.
Eccentric contraction
this involves the muscle lengthening whilst it is under tension. The origin and the insertion move further away from each other. An eccentric contraction provides the control of a movement on the downward phase and it works to resist the force of gravity.

Concentric contraction – the biceps are contracting concentrically to move the weights upwards.

Eccentric contraction – the biceps are contracting eccentrically to lower the weights against resistance.

Isometric contraction – this involves a muscle producing tension but staying the same length. This occurs when the body is fixed in one position.

Antagonistic muscle pairs

Muscle pairs

Muscles are attached to bones by tendons. They move our bones and associated body parts by pulling on them – this process is called muscle contraction.

Because muscle contraction cannot push a bone back into its original position, muscles must work together in ‘antagonistic muscle pairs’. One muscle of the pair contracts to move the body part, the other muscle in the pair then contracts to return the body part back to the original position.

In an antagonistic muscle pair, as one muscle contracts, the other muscle relaxes. The muscle that is contracting is called the agonist and the muscle that is relaxing is called the antagonist.

Key fact: one way to remember which muscle is the agonist – it’s the one that’s in ‘agony’ when you are doing the movement as it is the one that is doing all the work!

For example, when you perform a bicep curl, the bicep will be the agonist as it contracts to produce the movement, while the tricep will be the antagonist as it relaxes to allow the movement to occur.

Antagonistic muscle pairs

The following groups of muscles are antagonistic pairs:

Biceps and Triceps

Quadriceps and Hamstrings

muscular hypertrophy

When a person takes part in resistance exercises such as weight training, their muscle tissue is placed under stress. This causes micro tears in the muscle fibres. The body responds by repairing the muscle fibres and making them larger.

When a muscle gets bigger, the process is called hypertrophy.

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