The Structure of Body Systems
Why Body Systems Matter in Sport
Every movement you make in sport — a sprint finish, a tackle, a shot at goal — depends on at least four body systems working in harmony. Sport scientists, physiotherapists and coaches all need a solid understanding of how these systems are structured before they can make sense of how the body responds to exercise. This lesson focuses on the body system structures you are required to know: the skeletal system, the muscular system, the cardiovascular system and the respiratory system.
The Skeletal System
The skeleton is the body's rigid framework. It is made up of 206 bones in an adult and is divided into two main parts: the axial skeleton (skull, vertebral column, ribcage) and the appendicular skeleton (limbs, shoulder girdle, pelvis). Bones are classified by their shape. Long bones — such as the femur, humerus, tibia and fibula — act as levers during movement. Short bones (wrist and ankle bones) provide stability and support. Flat bones — the cranium, scapula, ribs and pelvis — protect vital organs. Irregular bones include the vertebrae of the vertebral column. The main bones you must know are: the cranium (skull), clavicle, scapula, humerus, radius, ulna, ribs, vertebral column, pelvis, femur, patella (kneecap), tibia and fibula.
The main bones you must know are: cranium, scapula, humerus, radius, ulna, ribs, vertebral column, pelvis, femur, patella, tibia and fibula. Work from head to toe and you will not miss any.
Types of Joint and Synovial Joint Structure
Where two or more bones meet, a synovial joint allows free movement. All synovial joints share the same basic structure: a joint capsule encloses the joint, lined by the synovial membrane which secretes synovial fluid to lubricate and nourish the articular cartilage. Articular (hyaline) cartilage covers the ends of bones, reducing friction. Ligaments connect bone to bone, stabilising the joint. The three synovial joint types you need to know are: ball and socket joints (shoulder and hip — allow movement in all planes), hinge joints (knee and elbow — allow flexion and extension only) and pivot joints (top of the vertebral column/atlas and axis — allow rotation).
A synovial joint contains six key structures that work together to allow smooth, pain-free movement. The joint capsule is a tough fibrous sleeve enclosing the whole joint. Inside it, the synovial membrane produces synovial fluid — a viscous liquid that lubricates and delivers nutrients to the articular cartilage. Articular cartilage (hyaline cartilage) coats the bone surfaces, reducing friction and absorbing compressive forces during impact. Ligaments are strong bands of connective tissue that hold bone to bone, preventing dislocation. Some joints also contain bursae (fluid-filled sacs) to cushion areas of friction, and in the knee, fibrocartilage menisci deepen the joint surface and distribute load.
The Muscular System
There are three types of muscle tissue in the body. Cardiac muscle is found only in the heart and contracts involuntarily and continuously throughout life. Smooth muscle lines internal organs such as blood vessels and the digestive tract and also works involuntarily. Skeletal (voluntary) muscle is attached to bones via tendons and is under conscious control — it is the type of muscle used in all voluntary sporting movements.
The major voluntary muscles you must locate are: biceps (front of upper arm — flexes the elbow), triceps (rear of upper arm — extends the elbow), deltoids (top of the shoulder — abducts the arm), pectorals/pectoralis major (chest — adducts and rotates the arm), abdominals (abdomen — flex the trunk and stabilise the core), quadriceps (front of the thigh — extends the knee), hamstrings (rear of the thigh — flexes the knee), gastrocnemius (calf — plantarflexes the ankle), gluteals/gluteus maximus (buttocks — extends and externally rotates the hip), and latissimus dorsi (broad muscle of the back — pulls the arm downward and backward). The spec also includes trapezius (upper back and neck — elevates and retracts the scapula).
The major muscle groups are: biceps, triceps, deltoids, pectorals, abdominals, quadriceps, hamstrings, gastrocnemius, gluteus maximus, latissimus dorsi and trapezius. For each one, know its location on the body.
Muscle Fibre Types
Skeletal muscle fibres are not all identical. The specification distinguishes two main types. Type I (slow-twitch) fibres contract slowly, generate less force but are very resistant to fatigue. They are rich in mitochondria and myoglobin, giving them a red appearance, and they rely predominantly on aerobic respiration. They are well suited to endurance activities such as marathon running or cycling. Type II (fast-twitch) fibres contract rapidly and generate greater force but fatigue quickly. They rely more on anaerobic respiration and are recruited during high-intensity, short-duration activities such as sprinting or weightlifting.
The Cardiovascular System
The cardiovascular system consists of the heart, blood vessels and blood. The heart is a four-chambered pump located in the chest cavity, slightly left of centre. The right atrium receives deoxygenated blood from the body via the vena cava. From there it passes through the tricuspid valve into the right ventricle, which pumps it to the lungs via the pulmonary artery. Oxygenated blood returns from the lungs through the pulmonary vein into the left atrium, then passes through the mitral (bicuspid) valve into the left ventricle — the most powerful chamber — which pumps blood around the entire body through the aorta. The left ventricle has much thicker walls than the right because it must generate higher pressure for systemic circulation.
Blood travels through three types of vessel. Arteries carry blood away from the heart at high pressure; their thick, elastic walls absorb the surge of pressure from each heartbeat. Veins carry blood back towards the heart at low pressure; they have thinner walls and contain valves to prevent backflow. Capillaries are microscopic, single-cell-thick vessels that form networks within tissues, allowing the exchange of oxygen, carbon dioxide and nutrients between the blood and cells. Blood itself is composed of red blood cells (carry oxygen via haemoglobin), white blood cells (immune defence), platelets (clotting) and plasma (the liquid carrying nutrients and waste).
Arteries have three distinct wall layers: a tough outer adventitia, a thick middle layer of smooth muscle and elastic tissue (tunica media), and a smooth inner endothelium. This construction allows them to expand and recoil with each heartbeat (the pulse you feel at your wrist is an artery). Veins share the same three layers but their tunica media is much thinner — they operate at low pressure and rely on skeletal muscle contractions and one-way valves to return blood to the heart. Capillaries are just one cell thick (endothelium only), with no muscle or connective tissue layers. Their tiny diameter (7–10 micrometres) means red blood cells pass through in single file, maximising contact time with surrounding cells for efficient gas and nutrient exchange.
The Respiratory System
The respiratory system draws oxygen into the body and expels carbon dioxide. Air enters through the nose and mouth and passes down the larynx (voice box) into the trachea (windpipe), a rigid tube kept open by C-shaped rings of cartilage. At the base of the trachea the airway divides into the left and right bronchi (singular: bronchus), each leading into its respective lung. Inside each lung the bronchi branch repeatedly into progressively narrower bronchioles, ending in tiny air sacs called alveoli.
The alveoli are the functional units of gas exchange: their enormous combined surface area (approximately 70 m² in an adult), moist thin walls and rich capillary network allow oxygen to diffuse from air into blood and carbon dioxide to diffuse from blood into air. The two lungs sit within the ribcage; the right lung has three lobes and the left lung has two (to accommodate the heart). Breathing itself is driven by the diaphragm — a dome-shaped sheet of skeletal muscle beneath the lungs. When it contracts and flattens, it increases thoracic volume, drawing air in (inspiration). When it relaxes and rises back, thoracic volume decreases, forcing air out (expiration). The intercostal muscles between the ribs assist this process by lifting and lowering the ribcage.