Functions of the skeleton

Your skeleton does far more than hold you up. For GCSE, learn these functions and link each to sport:

• Support — holds the body upright, giving shape and posture.
• Protection — the cranium protects the brain, the ribs protect the heart and lungs.
• Movement — bones act as levers that muscles pull on at joints.
• Structural shape & posture — e.g. height and frame for different sports.
• Mineral storage — stores calcium and phosphorus for strong bones.
• Blood cell production — red and white blood cells are made in the bone marrow.

Link it: strong bones (from weight-bearing exercise) resist fracture; red blood cells made in marrow carry the oxygen your muscles need.

Synovial joints & the structures that protect them

Most joints used in sport are synovial joints (freely moving). Learn each structure and its job — and don't muddle ligaments with tendons:

• Cartilage — smooth tissue on the ends of bones; reduces friction and absorbs shock.
• Synovial fluid — lubricates the joint so it moves freely.
• Synovial membrane — releases synovial fluid into the joint capsule.
• Ligaments — join bone to bone; hold the joint stable.
• Tendons — join muscle to bone; transfer the muscle's pull to the bone.

Exam trap: ligament = bone-to-bone, tendon = muscle-to-bone. Mixing these up is the most common lost mark here.

Ligament or tendon?

Muscles, antagonistic pairs & contraction types

Muscles can only pull (contract), not push, so they work in antagonistic pairs: as the agonist (prime mover) contracts, the antagonist relaxes.

• Elbow: biceps (flexion) ↔ triceps (extension).
• Knee: quadriceps (extension) ↔ hamstrings (flexion).
• Ankle: gastrocnemius (plantar-flexion) ↔ tibialis anterior (dorsi-flexion).

Contractions are also classified by what the muscle length does:

• Isotonic concentric — muscle shortens as it contracts (lifting up in a biceps curl).
• Isotonic eccentric — muscle lengthens under tension (lowering the weight with control).
• Isometric — muscle length stays the same (holding a plank).

Which muscle is the agonist?

The heart, blood vessels & vascular shunting

The cardiovascular system is the heart, blood and blood vessels. Blood follows a double circuit: to the lungs (pulmonary) and to the body (systemic).

• Arteries carry blood away from the heart (thick, muscular walls, high pressure).
• Veins carry blood back to the heart (valves stop backflow).
• Capillaries are tiny vessels where gas exchange with the tissues happens (thin, one-cell-thick walls).

During exercise, vascular shunting redirects blood to the working muscles: arteries to muscles vasodilate (widen) while those to the gut/skin at rest vasoconstrict (narrow).

Key terms: heart rate = beats per minute; stroke volume = blood pumped per beat; cardiac output (Q) = the two multiplied together.

Cardiac output — the equation

Training raises stroke volume, so a fit athlete pumps the same cardiac output at a lower resting heart rate (bradycardia).

Calculate cardiac output

Breathing & gaseous exchange

The respiratory system gets oxygen in and carbon dioxide out. Breathing is driven by the diaphragm and intercostal muscles changing the volume of the chest.

Gas exchange happens in the alveoli (tiny air sacs). Oxygen diffuses into the blood; carbon dioxide diffuses out. Alveoli are efficient because they have:

• a very large surface area;
• thin (one-cell-thick) walls — a short diffusion distance;
• a rich capillary blood supply keeping the gradient steep;
• a moist lining so gases dissolve.

Terms: tidal volume = air per normal breath; breathing rate = breaths per minute; minute ventilation = tidal volume × breathing rate.

Why alveoli work so well

Aerobic vs anaerobic exercise

Muscles need energy from respiration. Which type depends on the intensity and duration of the activity:

• Aerobic — lower intensity, longer duration (marathon, jogging). Uses oxygen.
• Anaerobic — high intensity, short duration (100 m sprint, a heavy lift). No oxygen; produces lactic acid.

EPOC / oxygen debt: after hard anaerobic work you keep breathing hard to take in extra oxygen that removes the lactic acid and restores the body.

Put each one in the right group

Tap each activity or fact, then tap whether it is mainly aerobic, mainly anaerobic, or true of both.

Short-term & long-term effects of exercise

Short-term (during / just after a session):

• heart rate, breathing rate and depth all increase;
• body temperature rises; you sweat and go red (skin vasodilation);
• muscles may fatigue and ache as lactic acid builds up.

Long-term (weeks/months of training):

• the heart gets bigger and stronger (cardiac hypertrophy) → higher stroke volume, lower resting HR;
• more capillaries and larger alveolar surface improve oxygen delivery;
• muscles get stronger and show greater muscular endurance and hypertrophy;
• bones and tendons/ligaments get stronger.

Minute ventilation

Match each statement to its answer

Tap a structure or term on the left, then its correct description on the right.

The big ideas to know

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