Learn the body.
Then use it.

Anatomical position & terms of location

• Anatomical position — standing upright, feet slightly apart and facing forward, head and eyes forward, arms by the sides, palms facing forwards. Every term and joint action below is described from this position. Get this wrong and half the joint actions invert.

The three planes of movement

Bone types

• The adult skeleton has 206 bones — 80 axial (skull, vertebral column, ribs, sternum) and 126 appendicular (limbs plus the shoulder and pelvic girdles).

Structure of a long bone

The vertebral column

• 33 vertebrae in five regions. 24 are movable; the sacral and coccygeal vertebrae are fused. The S-shaped curve acts as a spring, and the intervertebral discs provide shock absorption and elasticity.

Posture & postural deviations

• Neutral / optimal posture — the spine keeps its natural curves, hips and shoulders are level, weight is even through both feet, and head, neck and limbs are stacked so nothing is being held under constant strain. It improves balance, reduces injury risk and reduces everyday aches.

Five functions of the skeleton

• Support — the framework that gives the body shape and holds it upright.
• Movement — bones act as levers that muscles pull on via tendons.
• Protection — skull around the brain, rib cage around the heart and lungs, vertebrae around the spinal cord.
• Blood cell production — red bone marrow makes red cells, white cells and platelets. In adults it sits mainly in the spongy bone of flat bones and the ends of long bones; the shaft cavity holds yellow (fat-storing) marrow.
• Mineral storage — a reservoir of calcium and phosphorus, released into the blood as needed and used in muscle contraction and nerve function.

Levers & mechanical advantage

• The three parts: fulcrum (the joint), load / resistance (the body part plus any external weight), effort / force (the muscle contracting).
• Mechanical advantage means a smaller effort can move a larger load — you get it when the effort arm is longer than the load arm. Class 2 always has it; class 3 never does.

Bone growth, remodelling & bone health

• Bone is living tissue with its own blood supply — a collagen framework hardened by calcium and phosphorus salts. By weight it is roughly two-thirds mineral, one-third organic matrix and water. In the foetus most of the skeleton is cartilage; ossification replaces it with bone.
• Osteoblasts BUILD bone. Osteoclasts CLEAR it. Remodelling is the continuous balance between the two — a bone you load gets denser; a bone you don't gets thinner.
• Growth plates (epiphyseal plates) fuse progressively from the mid-teens — most long bones by about 16–18 in girls and 18–20 in boys, with some sites (iliac crest, clavicle, distal radius) not finishing until the early twenties. Until a plate closes it is the weakest part of the skeleton; once it does, it becomes the epiphyseal line.
• Peak bone mass is reached at about 25–30. Everything built before then is the reserve drawn on for the rest of life.
• Calcium is the mineral; vitamin D (sunlight, oily fish, fortified foods) is what lets you absorb it. Weight-bearing and resistance exercise is the stimulus that drives deposition.

Joints

• Synovial joint anatomy: a joint capsule encloses a joint cavity; the synovial membrane lining it secretes synovial fluid that lubricates the joint and feeds the cartilage; articular (hyaline) cartilage caps the bone ends to reduce friction and absorb shock; ligaments attach bone to bone and provide passive stability; bursae reduce friction where tendons cross bone.

Joint actions and their planes

The main joints, joint by joint

• Knee detail: the menisci (medial and lateral) deepen the joint and spread load; the cruciate ligaments (anterior and posterior) stop the tibia sliding forwards or backwards on the femur; the patella improves the quadriceps' angle of pull.
• Pelvis: three fused bones each side — ilium, ischium, pubis. The Q-angle between hip and knee is wider in a broader pelvis, which changes knee tracking and is worth watching in squats and lunges.

Three types of muscle tissue

• There are roughly 600–650 skeletal muscles, making up around 40% of body weight in men and a little less in women.

Structure of skeletal muscle — biggest to smallest

• Muscle — wrapped in epimysium.
• Fascicle — a bundle of muscle fibres, wrapped in perimysium.
• Muscle fibre (the muscle cell) — wrapped in endomysium.
• Myofibril — the contractile rod running the length of each fibre.
• Sarcomere — the basic contractile unit, one Z-line to the next, built from actin (thin) and myosin (thick) filaments.
• All three connective tissue layers merge at the ends of the muscle to form the tendon.

Muscle fibre types

• Everyone has all fibre types in every muscle; the proportion is largely genetic. Training changes the characteristics of fibres — and can shift IIx toward IIa — far more than it changes the overall split.
• Recruitment follows the size principle: type I units are recruited first, and type II units are only brought in as force demand rises. That is why intensity, not intention, determines which fibres you train.

Muscle roles in a movement

Types of contraction

• You are strongest eccentrically, then isometrically, then concentrically — which is why you can lower a weight you cannot lift.
• DOMS — delayed onset muscle soreness sets in around 12–24 hours after training and peaks at 24–72 hours. It is most strongly linked to unfamiliar eccentric work. It is a normal response to a new stimulus, not a measure of a good session.

Attachments

• Tendon — dense cord of connective tissue joining muscle to bone. (Ligament joins bone to bone — the pair most often mixed up.)
• Aponeurosis — a flat, sheet-like tendon, e.g. across the abdominal wall.
• Fascia — connective tissue sheets that wrap and separate muscles.
• Origin = the attachment that stays still, usually proximal. Insertion = the attachment that moves, usually distal.

Shoulder girdle & chest

The rotator cuff

• The glenoid fossa is a shallow socket, so the shoulder buys its enormous range at the cost of stability. Four small muscles hold the head of the humerus centred in the socket while the big muscles move it.

Arm

Trunk — spine & abdominals

Hip & pelvis

Leg

The core & pelvic floor

The heart

• About the size of a clenched fist, sitting behind the sternum and slightly left of centre. Its wall is cardiac muscle — the myocardium, which is involuntary and does not fatigue.
• Four chambers: two atria on top receive blood; two ventricles below pump it out. The left ventricle has by far the thickest wall — it has to push blood around the whole body.
• The heart feeds itself through the coronary arteries, which branch off the aorta. Blockage here is a heart attack.

Blood vessels

Blood flow through the heart

Blood

The numbers

Blood pressure

• Systolic — the peak pressure in the arteries as the ventricles contract. Diastolic — the resting pressure between beats. Recorded as systolic over diastolic in mmHg. The two systems disagree on where "high" starts, so use the one your qualification and country actually work to. The UK/NHS bands are what UK Level 3 papers key; the US moved its threshold down to 130/80 in 2017, which reclassified a lot of people overnight.

• What raises it acutely: exercise (especially heavy resistance work and the Valsalva manoeuvre), stress, caffeine, nicotine.
• What lowers it long term: regular aerobic exercise, weight loss, reduced sodium, reduced alcohol, stopping smoking, managing stress.
• Why it matters: chronic hypertension damages arterial walls and drives atherosclerosis (fatty plaque narrowing the artery) and arteriosclerosis (loss of elasticity), raising the risk of heart attack, stroke and kidney disease.
• Where the referral line sits. A reading of 140/90 or above (UK) or 130/80 or above (US) means a doctor referral before starting or progressing a programme. At 180/120 or above — a hypertensive crisis — do not train the client at all; that is a same-day medical referral. Many providers also withhold exercise above 180/110. And a fitness professional measures, but never diagnoses: a single high reading needs medical follow-up, not your judgement call. Follow whatever thresholds your qualification, employer and insurer specify — they override anything on this page.

The lymphatic system — the quiet second circulation

• Capillary exchange leaves fluid behind: about 3 litres a day filters out of the blood into the tissues and is not reclaimed by the veins. The lymphatic system collects it (now called lymph), filters it, and returns it to the blood near the heart — via the thoracic duct into the subclavian veins.
• It has no pump. Lymph vessels are thin-walled one-way streets with valves, moved along by the skeletal muscle pump, the pressure changes of breathing, and contractions of the vessel walls. Movement therefore is the lymphatic circulation — one reason long stillness shows up as swelling, and why exercise is part of lymphoedema management.
• Lymph nodes — clustered in the neck, armpits, groin and around the gut — filter lymph through beds of lymphocytes, which is why nodes swell when you are fighting an infection. The spleen, thymus and tonsils belong to the same defensive network.
• The gut's lymph vessels — the lacteals — do a second job from topic 09: they absorb dietary fat, packaged as chylomicrons, giving fat its slower, vein-bypassing route into the blood.
• Exercise and immunity: regular moderate exercise supports immune function, while very hard, prolonged work transiently suppresses it — one mechanism behind overtrained athletes catching everything (topic 08).

How it divides up

• Central nervous system (CNS) — brain and spinal cord. Receives, interprets, decides.
• Peripheral nervous system (PNS) — everything else, carrying signals in and out:
  • Sensory / afferent nerves carry information to the CNS
  • Motor / efferent nerves carry instructions from the CNS to muscles and organs
• The PNS splits again into:
  • Somatic — voluntary; skeletal muscle and conscious sensation
  • Autonomic — involuntary; organs, glands, smooth and cardiac muscle
• And the autonomic divides once more into sympathetic and parasympathetic.

Sensory receptors

The neuron

• The impulse: at rest the membrane is polarised (negative inside). A stimulus opens sodium channels, sodium floods in and the membrane depolarises. If it passes threshold, an action potential fires and travels the length of the axon. Potassium then moves out to repolarise it, and the sodium–potassium pump restores the resting state.

Motor units & the all-or-none law

• A motor unit is one motor neuron plus every muscle fibre it supplies. They meet at the neuromuscular junction.
• All-or-none law — when a motor neuron fires, every fibre in that unit contracts maximally, or none does. There is no partial contraction of a motor unit.
• So how do you produce a small force? By recruiting fewer units and firing them more slowly. Force is graded by how many units are active and how fast they fire — never by a unit contracting part-way.
• Precision vs power: eye and hand muscles have many tiny motor units (a few fibres each) for fine control. The quadriceps has large units (hundreds of fibres each) for gross force.
• Training improves recruitment, firing rate and synchronisation — which is why strength rises in the first few weeks before any measurable muscle growth.

Sliding filament theory

Proprioceptors & the two reflexes

The basics

• Glands secrete hormones — chemical messengers released into the bloodstream that act on target cells with the matching receptor.
• Nervous vs endocrine: nerves send electrical signals that act in milliseconds and stop quickly. Hormones travel in the blood, take seconds to hours, and last far longer. Together they run homeostasis — keeping temperature, blood glucose, blood pressure, fluid balance and pH within a working range.
• Three chemical classes: steroid hormones are made from cholesterol, are fat-soluble, slow-acting and long-lasting (testosterone, oestrogen, cortisol). Peptide / protein hormones are made from chains of amino acids, are water-soluble, fast-acting and short-lived (insulin, growth hormone). Amine hormones are built from a single amino acid — adrenaline and thyroxine — and adrenaline behaves like a peptide: water-soluble, fast and short-lived.
• Anabolic hormones build tissue up (testosterone, growth hormone, insulin). Catabolic hormones break it down (cortisol, glucagon, adrenaline). Training outcomes depend on the balance between the two over weeks, not on any single session.

Feedback loops

The glands

Blood glucose & diabetes

Hormones & training

The route air takes

• Nasal cavity / mouth → pharynx (throat) → larynx (voice box) → trachea (windpipe) → bronchi (one per lung) → bronchioles → alveoli.
• The first three are the upper respiratory tract; from the trachea down is the lower tract.
• Nasal breathing warms, humidifies and filters the air — worth cueing at rest and in warm-ups.
• The epiglottis is the flap that closes over the larynx when you swallow, keeping food out of the airway.
• There are roughly 300–500 million alveoli, each wrapped in pulmonary capillaries. Their combined surface area is around the size of a tennis court — that is why gas exchange is fast enough to keep up with exercise.

Gas exchange

The numbers

• The remainder in both cases is water vapour and trace gases — exhaled air is also warmer and much more humid. Note that nitrogen is not used: the same amount goes in and out.

Mechanics of breathing

Control of breathing

• Controlled involuntarily by the medulla oblongata in the brainstem, with voluntary override available.
• The main stimulus is rising carbon dioxide (detected as falling blood pH by chemoreceptors) — not falling oxygen. Low oxygen is a backup trigger, and matters mainly at altitude.
• Other inputs: stretch receptors in the lungs (the Hering–Breuer reflex, preventing over-inflation), proprioceptors in working muscles and moving joints, temperature, adrenaline, and conscious control.
• Long-term training adaptations: stronger, more fatigue-resistant respiratory muscles, greater maximal tidal volume, better gas exchange, and a lower breathing rate at any given workload. Note that vital capacity itself changes very little in healthy adults — what improves is how much of it you can use, and how efficiently.
• With age: lung tissue loses elasticity, alveolar surface area falls and the chest wall stiffens, so vital capacity declines.

ATP — the only currency

• Adenosine triphosphate is the only molecule a cell can use directly for energy. Adenosine plus three phosphates.
• Breaking off the third phosphate releases energy and leaves ADP (adenosine diphosphate) plus a free phosphate. ADP cannot power anything.
• Stored ATP lasts about 2–3 seconds of maximal effort. Everything else is about resynthesising it — sticking a phosphate back on.
• Three pathways do that. They are always all running; what changes is which one is dominant, and that is set by intensity above all.

The three systems side by side

Terms you will be asked to define

Fuels

• The crossover concept: as intensity rises, the mix shifts from mostly fat towards mostly carbohydrate. Low intensity burns a higher percentage of fat; higher intensity burns more total calories — and total energy balance is what changes body composition.
• UK-specific caps: total fat no more than 35% of food energy, saturated fat no more than 11%, and free sugars no more than 5%. The US sets ranges rather than caps, which is why the two columns above don't line up.
• Glycaemic index ranks carbohydrate foods by how quickly they raise blood glucose. Lower GI most of the time for steady energy; higher GI immediately after training when you want fast glycogen replacement.
• Scope note: the figures above are general public-health guidance. Writing individualised meal plans or prescribing macros to a client is dietetics, not a Level 3 scope of practice — and anyone with diabetes, kidney disease, an eating disorder or a pregnancy needs referral to a registered dietitian or their GP.
• Training the aerobic system increases mitochondria, capillaries, myoglobin and fat-oxidising enzymes — so a fitter person uses proportionally more fat at the same workload, sparing glycogen and lasting longer.

Training each system

• Acute (short-term) responses happen during and immediately after a session and reverse within hours. Chronic (long-term) adaptations are structural changes built over weeks and months of repeated training — and they reverse too, if you stop.

Acute responses

Long-term adaptations

Principles behind all of it

Risks and how to manage them

The route

• The alimentary canal (gastrointestinal tract): mouth → oesophagus → stomach → small intestine (duodenum, jejunum, ileum) → large intestine (colon, rectum) → anus.
• Accessory organs help but food never passes through them: salivary glands, liver, gall bladder, pancreas.
• Two kinds of breakdown happen throughout: mechanical (chewing, churning, and the emulsifying action of bile) and chemical (enzymes).
• Peristalsis — waves of smooth muscle contraction — moves food along the whole way. It is involuntary, run by the autonomic nervous system, and works even upside down.

What happens where

Enzymes and end products

Fibre, water and timings

• Insoluble fibre (wholegrains, wheat bran, vegetable skins, cellulose) adds bulk and speeds transit. Soluble fibre (oats, beans, apples, psyllium) forms a gel, slows glucose absorption and helps lower LDL cholesterol. Aim for 30 g a day in the UK; US guidance is 25 g for women and 38 g for men, or about 14 g per 1,000 kcal. Actual intake falls well short in both — around 19–20 g in the UK and about 16 g in the US.
• Total transit time is typically 24–72 hours: a few hours through the stomach and small intestine, then a day or more in the large intestine while water is reabsorbed.
• For training: a large or high-fat, high-fibre meal sits heavily and takes hours to clear — leave 2–4 hours before hard work. Blood is diverted away from the gut during exercise, which is why eating too close to a session causes cramping and nausea.

Children & adolescents

Pregnancy & postnatal

Older adults

• An untrained adult loses roughly 1–2% of physical capacity per year from around age 40. Almost none of that is inevitable — every item in the table below responds to training at every age.

Three groups

One rep, traced through every system

• You decide to stand up out of a squat. The brain sends an impulse down the spinal cord and out along motor neurons.
• At the neuromuscular junction, motor units fire. Calcium is released, cross-bridges form, and the sliding filament mechanism shortens the sarcomeres of the glutes and quadriceps.
• Those muscles pull on their tendons, which pull on bones acting as levers, rotating them about the hip and knee joints.
• The contraction consumed ATP, resynthesised by the energy systems from creatine phosphate, glycogen and fat.
• Those fuels came from food broken down by the digestive system and stored in muscle, liver and adipose tissue.
• Burning them aerobically needed oxygen from the respiratory system, delivered — and carbon dioxide removed — by the cardiovascular system.
• Throughout, the endocrine system is adjusting blood glucose, blood pressure, fuel mobilisation and temperature to hold homeostasis, and proprioceptors are feeding back position and tension so the movement stays coordinated.

Homeostasis, and why it explains the exam

• Homeostasis is keeping the internal environment stable — temperature, blood glucose, pH, blood pressure, fluid balance — while the outside world changes.
• Exercise is a deliberate disruption of homeostasis. Every acute response is the body correcting the disruption; every long-term adaptation is the body making the disruption easier to handle next time.
• That single idea is the answer to most "why does X happen during exercise?" questions: because a variable moved, and a system is correcting it.

When one system fails, others follow