1. Muscle Fibres
When we want to move our body, our brain sends signals to the special fibres within the muscles and these allow the movement to happen.
There are two different types of fibre in the muscles; fast twitch and slow twitch muscle fibres. Every person has a natural combination of both in their body and this amount cannot be changed.
1) Fast Twitch muscle fibres:
These are used in sports that require short bursts of energy. They contract fast (hence the name) and produce a powerful movement. They only have a limited oxygen supply and so tire quickly. They are best used for speed events, for throwing or for jumping.
2) Slow Twitch muscle fibres:
These are used in longer, endurance sports. They have a very good oxygen supply and this gives them large amounts of energy. They can contract any times and stay efficient over long periods. They are best used in long-distance running, cycling or swimming.
(GCSE PE: Unit 1.2.2)

2. Antagonistic Pairs Agonist/Antagonist
Muscles are arranged in antagonistic pairs, so when one muscle contracts and pulls, the other relaxes to allow the joint to work
For example; The biceps and triceps are arranged in an antagonistic pair to allow movement in the forearm.
Agonist/Antagonist
In these pairs, there is always an agonist and an antagonist. The agonist muscle is the contracting muscle and the antagonist is the relaxing muscle.
For example, when we extend our lower arm, the triceps contract (so it is the agonist) and the bicep relaxes (so it is the antagonist).
When we flex our lower arm, this muscles switch roles. The biceps contracts (so becomes the agonist) and the triceps relax (so they become the antagonist).
(GCSE PE: Unit 1.2.2)

3. Muscle Contractions
There are two main types of muscle contraction that you need to know:
Isotonic Contractions: These are contractions that cause a change in a muscles length. They are the main contraction we have spoken about so far. Examples include; a bicep curl, kicking a football, throwing a ball, doing a sit-up.
Isometric Contractions: This are contractions where the muscle length stays the same. They are used to keep the body steady, for example; doing a plank, handstands, pushing in a rugby scrum.
(GCSE PE: Unit 1.2.2)

4. Immediate Effects of Exercise on the Muscular System
Exercise has a number of effects on our muscles. As soon as we start exercising, our muscles start to feel some of those effects:
Muscle Fatigue: Muscles begin to get tired as our ability to use oxygen becomes less efficient.
Lactic Acid build-up: Anaerobic exercise causes lactic acid to build up due to the lack of oxygen – this causes pain and cramp.
Increase in muscle temperature.
Increase in C02 production.
(GCSE PE: Unit 1.2.2)

5. Long-term Effects of Exercise on the Muscular System
Exercise has a number of effects on our muscles. If we train our muscles over time the following effects happen:
Muscle Hypertrophy: Muscles increase in size and strength – which leads to increased power, muscular strength and muscular endurance.
Increase in myoglobin stores: Myoglobin helps store oxygen in the muscles. Extra myoglobin improves oxygen supply and means more energy can be made with every contraction.
Tendons and Ligaments get stronger: Tendons and ligaments hold the muscles in place. They get stronger and this makes them thicker and more flexible, giving better joint support.
(GCSE PE: Unit 1.2.2)

6. Muscle Injuries
When exercising, there is always a risk of muscular injury.
Soft Tissue Injuries: There are two main types here; strains and sprains.
- Strains: occur when a muscle is overstretched or torn (eg
a pulled muscle).
- Sprains: occur when ligaments are overstretched or torn
around a joint (eg twisted or sprained ankle).
Overuse Injuries: These are caused by using a part of the body again and again. They damage the tendons and an example is tennis elbow.
(GCSE PE: Unit 1.2.2)

7. Muscle Injuries - Prevention
There are a number of steps you can take to prevent injury:
Warm-up: Allows the muscles to warm-up (extra blood flow) and avoid strains.
Cool-down: Allows the muscles to cool down slowly and prevents lactic acid build up.
Rest: This prevents overuse injuries. It also allows muscles time to repair themselves. HOWEVER, too much rest can lead to muscle atrophy (where muscles get smaller and weaker – just like Mr Drake).
(GCSE PE: Unit 1.2.2)