The Functions of Body Systems

Why Functions Matter

Understanding how each body system works is the foundation of sport science. Coaches, physiotherapists and athletes all need to know what each system does — not just what it is made of — so they can explain why performance improves with training, or why it breaks down with fatigue. This lesson examines the four key systems: skeletal, muscular, cardiovascular and respiratory, and explores the specific jobs each one carries out during sport and exercise.

Functions of the Skeletal System

The skeletal system performs six important functions. First, it provides support — the vertebral column and leg bones act as a structural framework that holds the body upright against gravity, which is essential for every sporting activity from swimming to weightlifting. Second, it offers protection to vital organs: the cranium shields the brain, the ribcage guards the heart and lungs, and the vertebral column protects the spinal cord. Third, bones create movement through levers — they act as rigid levers that muscles pull on to generate movement at synovial joints. Every time a sprinter drives their leg backward or a tennis player swings their racket, a lever system is at work.

Fourth, the skeleton provides the body with its structural shape — the characteristic human silhouette is determined by bone structure, and this shape influences posture and aerodynamic efficiency in sport. Fifth, certain bones — particularly the long bones such as the femur and humerus, and flat bones such as the sternum — contain red bone marrow that carries out blood cell production. Red blood cells manufactured here carry oxygen to working muscles, making this function directly relevant to aerobic performance. Sixth, bones act as a mineral store, holding approximately 99% of the body's calcium and significant amounts of phosphorus. These minerals are released into the bloodstream when needed and are also essential for normal muscle contraction.

Functions of the Muscular System

The muscular system's primary function is to produce movement through contraction. Muscles can only pull — they cannot push — so they are arranged in antagonistic pairs. At the elbow, the biceps acts as the agonist during flexion, shortening to bend the arm, while the triceps acts as the antagonist and relaxes to allow the movement. During extension — for example, a basketball chest pass — the roles reverse. The specification requires knowledge of antagonistic action at both the elbow and the knee (quadriceps and hamstrings). Muscles also have synergist muscles that assist the agonist, and fixator muscles that stabilise the joint to allow efficient movement.

Beyond movement, the muscular system maintains posture — deep postural muscles such as the abdominals, erector spinae and trapezius are in a state of continuous partial contraction to hold the body in alignment during both rest and activity. Good posture reduces injury risk and improves mechanical efficiency in sport. The muscular system also plays a major role in generating heat. Muscle contractions are only about 25% mechanically efficient — the remaining 75% of the energy released is lost as heat. This thermogenic function helps the body maintain its core temperature during exercise in cold environments, which is why vigorous activity warms you up rapidly.

Functions of the Cardiovascular System

The cardiovascular system (the systemic circulatory system) has three core functions. Its primary role is the transport of oxygen and nutrients to working muscles and organs. During exercise, cardiac output increases — the heart beats faster and pumps more blood per beat (stroke volume) — so that oxygen and glucose reach the muscles rapidly enough to sustain contraction. Without this delivery, muscles would switch to anaerobic metabolism and fatigue rapidly.

The second function is the removal of waste products, including carbon dioxide and lactic acid produced during exercise. Deoxygenated blood carrying CO2 returns via the veins to the right side of the heart, from where it is pumped to the lungs (the pulmonary circuit) to release CO2 and collect fresh oxygen. Lactic acid is transported to the liver for conversion. The third function is regulation of body temperature. When the body overheats during exercise, vasodilation occurs — blood vessels near the skin surface widen, bringing warm blood to the surface where heat can be lost to the environment. When the body is cold, vasoconstriction narrows these vessels to retain core heat. This temperature-regulation mechanism is directly assessable in the written examination.

Functions of the Respiratory System

The respiratory system drives breathing — the mechanical process of moving air in and out of the lungs. During inspiration (breathing in), the diaphragm contracts and flattens while the intercostal muscles between the ribs contract to lift the ribcage outward and upward, increasing the volume of the thoracic cavity. This reduces internal air pressure below atmospheric pressure, so air rushes into the lungs. During expiration (breathing out), the diaphragm and intercostal muscles relax, the ribcage drops inward and downward, volume decreases, pressure rises and air is forced out. At rest this happens around 12-20 times per minute; during intense exercise breathing rate can exceed 40-50 breaths per minute.

The second and most critical function is gaseous exchange at the alveoli. The alveoli are surrounded by a dense network of capillaries. Oxygen diffuses from the high concentration inside the alveoli across the thin alveolar wall into the blood (where oxygen concentration is lower), binding to haemoglobin in red blood cells. At the same time, carbon dioxide — in high concentration in the blood after being produced by working muscles — diffuses in the opposite direction, from the blood into the alveoli, and is then expelled during expiration. This process of diffusion is passive and depends on the concentration gradient being maintained: the continuous flow of blood removes oxygenated blood and brings fresh deoxygenated blood, keeping the gradient steep and exchange efficient.