Welcome to the Muscular System!
Ever wondered how a footballer generates explosive power to strike a ball, how a gymnast holds a rock-solid plank, or how a marathon runner keeps going for over 26 miles? The answer lies in your muscular system.
In this chapter of The Body at Work for CCEA GCSE PE, you will learn how muscles work, how they are classified, how they work together in pairs to produce sporting actions, and why different athletes need different muscle fibre types. Don't worry if anatomy sounds complicated at first—we will break down every single muscle and movement step by step!
1. The Three Muscle Classifications
The human body contains three distinct types of muscle tissue. Each has a special job and unique characteristics:
1. Skeletal Muscle (Voluntary / Striated Muscle)
• Where is it? Attached directly to the skeleton by tendons.
• Control: Under voluntary (conscious) control—you decide when to move them.
• Fatigue: They fatigue (get tired) with repeated contractions during physical activity.
• Function: Responsible for creating sporting movement and maintaining posture (e.g., your biceps flexing your arm during a bicep curl).
2. Cardiac Muscle
• Where is it? Found exclusively in the wall of the heart (the myocardium).
• Control: Involuntary—it works automatically without you having to think about it, controlled by your autonomic nervous system.
• Fatigue: It is non-fatiguing under normal conditions (it pumps continuously throughout your life!).
• Function: Contracts rhythmically to pump blood around the body.
3. Smooth Muscle (Involuntary Muscle)
• Where is it? Found inside the walls of internal organs and blood vessels.
• Control: Involuntary and contracts slowly.
• Function: Controls essential automatic body functions, such as digesting food or altering blood flow via vasoconstriction (narrowing) and vasodilation (widening) of blood vessels.
Key Takeaway: Skeletal muscle is voluntary and fatigues; cardiac and smooth muscles are involuntary, and cardiac muscle does not fatigue!
2. Connective Tissues: Connecting the System
To produce movement, bones, joints, and muscles must be linked together. There are three essential connective tissues you must know for your exam:
• Tendons: Tough, non-elastic fibrous bands that attach muscle to bone. When a muscle contracts, the tendon pulls on the bone to create movement.
• Ligaments: Strong, slightly elastic fibrous bands that connect bone to bone across a joint. They hold the joint together, stabilize it, and prevent unwanted movements or dislocations.
• Cartilage: Smooth, durable tissue covering the ends of bones at synovial joints. It acts as a shock absorber and reduces friction so bones do not rub painfully against each other.
Helpful Memory Aid:
• Tendons = Two different tissues (Muscle to Bone)
• Ligaments = Like to Like (Bone to Bone / Link bones)
3. Major Skeletal Muscles and Sporting Actions
For your CCEA exam, you need to identify where major skeletal muscles are located and name the primary sporting movement they produce:
Upper Body & Trunk Muscles
• Deltoids (Shoulder): Abduction, flexion, and extension of the upper arm at the shoulder joint.
Sporting Example: The arm recovery phase in swimming or raising the arms laterally in gymnastics.
• Pectoralis Major (Chest): Flexion and horizontal adduction of the arm across the chest.
Sporting Example: Pushing the ball forward during a chest pass in netball or basketball, or performing a bench press.
• Latissimus Dorsi (Back / Upper Trunk): Adduction and extension of the upper arm at the shoulder joint.
Sporting Example: The pulling phase in rowing or the underwater pull in freestyle swimming.
• Trapezius (Upper Back / Neck): Elevation and retraction of the shoulder blades (scapulae).
Sporting Example: Shrugging the shoulders or holding the head and neck firm and upright during a rugby scrum.
• Biceps Brachii (Front of the Upper Arm): Flexion of the forearm at the elbow joint (bending the arm).
Sporting Example: Pulling up during a chin-up or bending the elbow during a bicep curl.
• Triceps Brachii (Back of the Upper Arm): Extension of the forearm at the elbow joint (straightening the arm).
Sporting Example: Straightening the arm to throw a javelin or executing a push pass in hockey.
• Abdominals / Rectus Abdominis (Stomach / Anterior Trunk): Flexion of the trunk/spine.
Sporting Example: Pulling the torso up in a sit-up or executing a pike jump in gymnastics.
Lower Body Muscles
• Gluteals / Gluteus Maximus (Buttocks): Extension and hyperextension of the leg at the hip joint.
Sporting Example: Driving the leg backward when sprinting or pushing upward when jumping.
• Quadriceps (Front of the Thigh): Extension of the leg at the knee joint (straightening the knee).
Sporting Example: Straightening the leg to kick a football or driving upward out of a squat.
• Hamstrings (Back of the Thigh): Flexion of the leg at the knee joint (bending the knee).
Sporting Example: Bending the knee in the backswing before kicking a ball or the heel-flick phase while sprinting.
• Gastrocnemius (Calf / Back of Lower Leg): Plantar flexion at the ankle (pointing toes downwards / pushing onto balls of feet) and assists knee flexion.
Sporting Example: Pushing off the starting blocks in sprinting or jumping up for a rebound in basketball.
• Tibialis Anterior (Shin / Front of Lower Leg): Dorsiflexion at the ankle (pulling toes upward toward the shin).
Sporting Example: Lifting the toes to clear the ground during a running stride.
4. How Muscles Produce Movement: Antagonistic Pairs
The Golden Rule of Muscles: Muscles can ONLY PULL by contracting; they can NEVER PUSH. Because a muscle cannot push a bone back into its starting position, skeletal muscles must work in antagonistic pairs.
Key Movement Roles:
• Agonist (Prime Mover): The muscle that contracts and shortens to produce the desired movement.
• Antagonist: The opposing muscle that relaxes and lengthens to allow the movement to take place smoothly.
• Fixator: A muscle that contracts statically/isometrically to stabilize a bone or nearby joint, giving the agonist a solid base to pull against (e.g., the trapezius stabilizing the shoulder blade during a bicep curl).
Core Exam Pairs to Memorise:
1. Elbow Joint
• Flexion (bending arm): Agonist = Biceps | Antagonist = Triceps
• Extension (straightening arm): Agonist = Triceps | Antagonist = Biceps
2. Knee Joint
• Flexion (bending knee): Agonist = Hamstrings | Antagonist = Quadriceps
• Extension (straightening knee): Agonist = Quadriceps | Antagonist = Hamstrings
3. Ankle Joint
• Plantar Flexion (pointing toes down): Agonist = Gastrocnemius | Antagonist = Tibialis Anterior
• Dorsiflexion (pulling toes up): Agonist = Tibialis Anterior | Antagonist = Gastrocnemius
5. Types of Muscle Contraction
When a muscle creates tension, it can do so in different ways depending on whether movement occurs.
1. Isotonic Contractions (Movement Occurs)
In an isotonic contraction, muscle tension produces movement at a joint and the muscle changes length. There are two types:
• Concentric Contraction: The muscle shortens under tension while overcoming a resistance.
Example: Upward phase of a bicep curl (the biceps shortens as you lift the weight), or pushing up during a press-up.
• Eccentric Contraction: The muscle lengthens under tension while controlling or resisting a load.
Example: Downward phase of a bicep curl (the biceps lengthens under control to lower the weight safely), or lowering yourself down during a press-up or squat.
2. Isometric Contractions (No Movement)
In an isometric contraction, the muscle develops tension and exerts force, but does not change length and there is no movement at the joint.
Sporting Examples: Holding a plank, holding a static rugby scrum, or holding a pause at the bottom of a wall sit.
Quick Summary:
• Concentric: Muscle shortens under tension.
• Eccentric: Muscle lengthens under tension.
• Isometric: Muscle stays the same length under tension (static).
6. Muscle Fibre Types
Skeletal muscles are made up of individual fibres. Humans have two main types of muscle fibres, each suited for different sports:
Type I: Slow-Twitch Fibres
• Characteristics: Slow contraction speed, low force production, high resistance to fatigue.
• Structural Features: High capillary density (rich blood supply), high myoglobin content, and high number of mitochondria (aerobic energy factories).
• Best Suited For: Continuous, aerobic endurance activities where energy is needed over a long period.
• Sporting Examples: Marathon runners, long-distance cyclists, cross-country skiers.
Type II: Fast-Twitch Fibres (Type IIa and Type IIx)
• Characteristics: Fast contraction speed, high power and force generation, but low resistance to fatigue (they fatigue rapidly).
• Structural Features: Lower capillary density and lower myoglobin content.
• Best Suited For: Explosive, anaerobic activities requiring maximum power in short bursts.
• Sporting Examples: 100m sprinters, shot putters, Olympic weightlifters, high jumpers.
7. Common Exam Pitfalls & Examiner Tips
Make sure you don't lose easy marks by watching out for these common mistakes reported by examiners:
1. Never say "muscles push":
Muscles can only pull by contracting. To return a joint to its original position, the opposite muscle in the antagonistic pair must pull.
2. Don't mix up Tendons and Ligaments:
Remember: Tendons attach muscle to bone; Ligaments attach bone to bone.
3. Be precise with Concentric vs. Eccentric:
Remember that an eccentric contraction is still an active contraction with tension—the muscle is actively working to resist gravity or control a load as it lengthens.
4. Static does not mean relaxed:
During an isometric contraction (like a scrum or a plank), muscles are working extremely hard and producing high tension, even though no joint is moving.
Quick Review Checklist
Can you answer these key revision questions?
• Can you name the 3 muscle types and identify which ones are voluntary and involuntary?
• What is the difference between a tendon and a ligament?
• What muscle acts as the agonist during knee extension when kicking a football?
• What is the difference between a concentric and an eccentric muscle contraction?
• Which muscle fibre type would a 100m sprinter rely on, and why?