Muscles and movement
The heart is made of a unique muscle type known as cardiac and it never tires. But the body also has many other paired muscles, some voluntary that are attached to the skeleton and help the body move, some involuntary that work the internal organs and cannot be controlled. Muscles and posture also go hand in hand, where regular exercise tones muscle and improves your posture to reduce strain on other parts of the body.
Cardiac muscle is unique to the heart. It never tires.
The body's involuntary muscles work our internal organs. They are outside our control.
Voluntary muscles make the body move. They are attached to the skeleton and can be controlled.
Voluntary muscles have fast twitch and slow twitch fibres. Fast twitch fibres contract quickly, but do not use oxygen well and tire quickly. Slow twitch fibres contract slowly, but use oxygen well and keep going for a long time. Top sprinters have more 'fast twitch' fibres. Endurance athletes tend to have more 'slow twitch' fibres.
The key voluntary muscles used in sport are shown in the illustration.
|Name of muscle||Function||Example in sport|
|Triceps||Extend the arm at the elbow||Press-up, throwing a javelin|
|Biceps||Flex the arm at the elbow||Pull-up, drawing a bow in archery|
|Deltoids||Move the arm in all directions at the shoulder||Bowling a cricket ball|
|Pectorals||Adduct the arm at the shoulder||Forehand drive in tennis|
|Trapezius||Hold the shoulders in place, move head back and sideways||Holding head up in rugby scrum|
|Gluteals||Adduct and extend leg at the hips||Pulling back leg before kicking a ball|
|Quadriceps||Extend the leg at the knee||Kicking a ball jumping upwards|
|Hamstrings||Flex the leg at the knee||Bending knee before kicking a ball|
|Gastrocnemius||Pointing the toes, help to flex the knee||Running|
|Latissimus dorsi||Adduct and extend the arm at the shoulder||Butterfly stroke in swimming|
|Abdominals||Flex the trunk across the stomach||Pulling the body down when hurdling|
Origin and insertion of muscles (AQA only) The origin is the end of a muscle which is attached to a fixed bone. The insertion is the end of the muscle that is attached to the bone which moves.
Muscles contract [Contract: A muscle tenses as fibres shorten. ] when they work. If a muscle contracts to create movement, it is called an isotonic contraction.
An isotonic contraction can be concentric, which is where the muscle shortens as the fibres contract or eccentric, where the fibres contract as the muscle lengthens.
When a muscle contracts with no resulting movement, it is an isometric contraction.
Antagonistic pairs of muscles create movement when one (the prime mover) contracts and the other (the antagonist) relaxes. Examples of antagonistic pairs working are:
Muscle tone can be seen when muscles are in a state of slight tension and they are ready for action. Regular training tones muscles and helps to create good posture [Posture: The way you hold your body in position. ]. In addition, muscles will hypertrophy (increase in size) and develop better endurance [Endurance: The ability to work hard for long periods of time. ].
Muscle tone developed by regular exercise makes daily tasks such as shopping and gardening easier. It also helps to prevent injury as good posture reduces the strain on muscles, tendons and ligaments.
Good posture helps with sporting performance as special positions are often crucial to success, eg the position throughout the golf swing.
People with good posture also feel better about themselves. An upright body position is often a sign of self confidence. People who are less confident will sometimes show this in their body language, for example by adopting a slouched posture.