Human Body Systems: Anatomy and Physiology for Performance

Posted on Aug 13, 2025 in Biology

Skeletal System Functions

• Protects the body’s organs: Ribs and sternum protect the heart and lungs; the cranium protects the brain; the pelvis protects the intestines.

• Allows movement: Movement is achieved through the use of joints and muscle attachment. Without the ability to use our muscles for movement, sports would be impossible to play.

• Helps formation of blood cells: Platelets, red blood cells, and most white blood cells are produced in the bone marrow.

• Stores minerals: Bones store calcium and phosphorus. These minerals are necessary to keep bones healthy.

Bone Classifications and Functions

• Long bones: Longer in length than in width, they act as levers, allowing us to move.

• Short bones: Box-shaped bones, they are as long as they are wide.

• Flat bones: These bones are normally flat, thin, and curved. They provide protection and a large surface area for muscle attachment.

• Irregular bones: Used for protection and attachment. Bones that do not fit into the other categories are classified as irregular.

Vertebral Column: Bones and Structure

Cervical Vertebrae

• The first vertebra, called the atlas, supports the weight of the head and allows us to nod up and down.

• The second vertebra, the axis, allows us to rotate our heads (e.g., shaking our heads ‘no’).

• The remaining cervical vertebrae allow for muscle attachment, providing the most movement within the vertebral column.

Thoracic Vertebrae

These vertebrae allow for no movement, primarily serving to protect the heart and lungs and to attach and support the rib cage.

Lumbar Vertebrae

The largest individual vertebrae, they are crucial for:

• Support body weight

• Muscle attachment

Sacral Vertebrae

The sacral vertebrae are fused together to form the sacrum, which:

• Transmits body weight to the pelvis

Spine’s Movements

• Flexion: Bending forward

• Extension: Bending backward

• Lateral Flexion: Bending sideways

• Rotation: Twisting and turning

Vertebral Column in Sport

• Movement of the head, aided by the cervical vertebrae, to improve technique.

• Protection of the heart and lungs by the thoracic vertebrae.

• Muscle attachment allowing for flexion, extension, or rotation as required by athletic technique.

• Weight bearing for athletes (e.g., sprinters) supported by the sacral vertebrae.

Tendons: Attach muscles to bones. They are flexible, facilitating movements like flexion and extension.

Ligaments: Tough, elastic fibers that connect bones to bones. Joints are classified based on the amount of movement they allow.

Cartilage: Prevents the ends of bones from rubbing together at a joint.

Movement at Joints

Major Joints and Associated Bones

• Neck: Atlas and Axis
• Elbow: Humerus, Radius, and Ulna
• Knee: Femur, Tibia, Patella
• Ankle: Tibia, Talus, Fibula
• Hip: Ilium, Ischium, Pubis, and Femur
• Shoulder: Humerus and Scapula
• Wrist: Radius, Scaphoid, Lunate, and Triquetrum

Muscular System and Physical Activity

Muscles are involved in every movement in your body. Muscles are a special type of tissue made up of fibers that contract and relax.

Muscle Classification

• Voluntary muscles: Attached to bones, they work whenever we consciously control them.

• Involuntary muscles: Found on the walls of internal organs, they contract in waves. They work without conscious control or awareness.

• Cardiac muscles: A special type of muscle that forms the walls of the heart chambers. It contracts without conscious thought or effort; it does not stop and never tires. When it contracts, it pumps blood out of the heart and around the body.

In an antagonistic muscle pair, as one muscle contracts, the other muscle relaxes or lengthens. The muscle that is contracting is called the agonist, and the muscle that is relaxing or lengthening is called the antagonist.

Muscle Fiber Types

Muscle fiber types occur in different proportions in different people. This proportion is primarily determined by inherited genes but can be altered through training.

There are two main types of muscle fibers:

• Slow-twitch muscle fibers: Small in size. These fibers take a relatively long time to contract.

• Fast-twitch muscle fibers: Large in size, contract quickly and powerfully.

Slow-twitch muscle fibers (Type I): Typically make up about 60% of muscle fibers.

• Have a good oxygen supply due to large amounts of myoglobin, mitochondria, and a dense capillary network.

• They contract slowly and can work for long periods, making them ideal for aerobic activities.

Fast-twitch muscle fibers (Type II): Typically make up about 40% of muscle fibers.

• Have a limited oxygen supply, making them suited for anaerobic activities.

• Contract quickly and powerfully, but tire easily.

• Type IIa fibers are mixed, possessing properties of both Type I and Type IIx. With appropriate training, these muscle fiber types are thought to adapt for either endurance or power.

• Type IIx fibers fatigue easily as they lack the myoglobin, mitochondria, or extensive capillary network of slow-twitch fibers and Type IIa. Therefore, they are best suited for events requiring speed or large amounts of force.

Cardiovascular System

The Heart

The heart works continuously throughout our lives. In an average lifetime, it can beat over three billion times. The heart rate increases significantly during exercise to meet the body’s demands.

The heart is made up of four chambers:

The left and right atria (upper chambers) receive blood into the heart and pass it on to the ventricles when they contract.

The left atrium receives oxygenated blood from the lungs through the pulmonary vein, while the right atrium receives deoxygenated blood from the body through the vena cava.

The left and right ventricles (lower chambers) receive blood from the atria above them. Once filled, they contract to force blood out of the heart.

The left ventricle has a thicker muscular wall because it performs the most work, pumping blood out of the heart via the aorta to the rest of the body.

The aorta is the main artery carrying oxygenated blood from the left ventricle to the rest of the body.

The right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery to pick up oxygen.

The heart contains valves that ensure blood flows in only one direction, preventing backflow.

Oxygenated blood means that red blood cells have collected oxygen from the lungs. Deoxygenated blood means that the oxygen carried by the blood has been delivered to tissues for energy release.

The Tricuspid valve is located on the right side of the heart, separating the right atrium from the right ventricle and allowing blood to flow from the atrium to the ventricle.

The Bicuspid valve (or Mitral valve) is on the left side of the heart, separating the left atrium from the left ventricle. It allows blood to flow from the left atrium to the left ventricle but prevents backflow.

The Semilunar valves are the remaining valves, located between the left ventricle and the aorta (aortic valve), and between the right ventricle and the pulmonary artery (pulmonary valve). They allow blood to exit the ventricles and flow out of the heart but prevent it from returning.

The Septum is the muscular wall that divides the heart into two sides (left and right). The right side contains deoxygenated blood from the body, while the left side contains oxygenated blood. If these blood types were to mix, the amount of oxygen delivered to the muscles would decrease, impairing energy release for physical activity.

Double Circulatory System

The heart circulates blood in two distinct pathways: from the heart to the lungs and back (pulmonary circulation), and from the heart to the rest of the body and back (systemic circulation). These two interconnected circuits form what is known as a double circulatory system.

Blood Pressure

As blood moves through blood vessels, it exerts a force on their walls. The strength of this force is your blood pressure. As blood circulates further from the heart, this force is reduced; thus, blood pressure decreases as blood moves from arteries into capillaries and then into veins. When blood pressure is measured, arterial blood pressure is typically used.

If blood pressure is too high (hypertension), it puts extra strain on arteries, which can lead to serious health issues like heart attacks or strokes.

When the ventricles contract, blood pressure is at its greatest; this is called systolic blood pressure. When the ventricles are filling, blood pressure is lower; this is the diastolic blood pressure.

Heart Rate

Heart rate is the number of times the heart beats per minute. Each time the heart beats, the ventricles contract, squeezing blood out into the lungs or the body. During exercise, the rate of blood flow increases, allowing for quicker delivery of oxygen to working muscles and removal of waste products like CO2. This enables an individual to maintain a higher intensity of work than at rest, leading to an increased heart rate.

Stroke Volume

When the ventricles contract, they do not empty completely; only about 60% of the blood is ejected. With regular exercise, the muscular walls of the ventricles become stronger, allowing them to contract more forcibly and eject more blood with each beat. This is why stroke volume (the amount of blood pumped out by one ventricle per beat) increases with regular exercise. This training-induced increase in stroke volume also explains why fit individuals often have lower resting heart rates than those who do not train.

Cardiac Output

At rest, approximately 5 liters of blood circulate through our bodies per minute. During intense exercise, this can increase to 30 liters per minute to ensure sufficient oxygen delivery.

Cardiac Output = Stroke Volume × Heart Rate

Vascular Shunting

At rest, sufficient blood circulates to meet the body’s needs. However, blood flow varies depending on specific demands. For instance, after eating, there’s an increased need for blood flow to the digestive system, which reduces the amount available for skeletal muscles. This presents a challenge during exercise, as insufficient oxygen would be delivered to the muscles. To overcome this, the body employs two main mechanisms:

• Increase cardiac output by increasing heart rate.

• Redistribute blood flow so that a greater percentage flows to the working muscles.

The process of redistributing blood, known as vascular shunting, is achieved through:

• Vasodilation: Widening of blood vessels to increase blood flow.

• Vasoconstriction: Narrowing of blood vessels to decrease blood flow.

Blood Vessels

Blood vessels carry blood to and from all living cells in the body. There are different types, each with a specific function and a structure optimized for that role.

Arteries

• Carry blood away from the heart.

• They are made up of three layers: an outer tough layer, a middle muscular layer, and a smooth inner layer to facilitate blood flow.

• Carry blood at a higher pressure because they transport it directly from the heart.

• They have thick muscular walls.

• They pulsate: when the heart contracts, the arterial walls expand, and then recoil to push blood forward.

• Generally carry oxygenated blood (except for the pulmonary artery).

Veins

• The main veins include the vena cava.

• Carry blood towards the heart at a low pressure.

• Have valves to prevent backflow.

• Have thin walls.

• Have a larger internal lumen (diameter) than arteries.

• Generally carry deoxygenated blood (except for the pulmonary veins).

Capillaries

• Blood flows from arteries to veins via capillaries.

• Carbon dioxide diffuses from tissues into the blood, and oxygen diffuses from the blood into tissues.

• They are one cell thick and very fragile.

• Blood cells pass through them one cell at a time.

Blood Components

Blood is made up of red blood cells, white blood cells, platelets, and plasma. Adults typically have around 5.5 liters of blood.

• White blood cells: Responsible for seeking out and destroying infections. White blood cells can slide through blood vessel walls to attack bacteria, helping to keep individuals healthy.

• Red blood cells: Contain hemoglobin, which allows for the transportation of oxygen.

• Plasma: The liquid part of the blood, primarily made of water. Plasma allows solid blood cells to flow throughout the body, essentially giving them a ‘ride’.

• Platelets: Crucial for maintaining health, especially for athletes, as they aid in blood clotting.

Respiratory System

Components of the Respiratory System

Air enters the body passing through the mouth and nasal passages. It is generally better to breathe through the nose than the mouth because:

• The nose has a filter to remove dust particles from the air.

• Warms the air to body temperature.

• Moistens the air, ensuring it arrives at the lungs saturated with water.

After leaving the nasal passages, air flows into the larynx. From there, it passes through the trachea into the right or left bronchus. From the bronchi, the air travels into the bronchioles and finally reaches the alveoli.

Gas exchange takes place in the alveoli. This is the swapping of oxygen and carbon dioxide, driven by the pressure gradients of each gas at the exchange site. The percentage of oxygen in the lungs is much higher than in the surrounding blood vessels.

Regular endurance training can lead to an increase in the number of alveoli in the lungs and an increase in the capillaries available for gas exchange.

An increase in alveoli means that an individual can diffuse more oxygen into the blood, provided these alveoli have access to a sufficient blood supply for gas exchange.

Expiration and Inspiration

The movement of the diaphragm and the ribs facilitates the movement of air into and out of the lungs.

During expiration (breathing out), the lungs slightly deflate. As this occurs, the lungs occupy less space, allowing the ribs to move downwards and inwards, and the diaphragm to relax. This helps the lungs expel air.

During inspiration (breathing in), the lungs need to expand to hold more air, similar to a balloon being inflated. To create this space, the diaphragm contracts, and the ribs move up and out due to the contraction of the external intercostal muscles.

While the lungs themselves do not increase in size with regular training, intensive exercise will fatigue the diaphragm and external intercostal muscles. This leads to their adaptation, making them stronger and more capable of handling the demands of physical activity. Due to the increased strength of these muscles, tidal volume (the amount of air inhaled or exhaled during a normal breath) can be increased.

Lever Systems

All lever systems are made up of four components:

• Load: The object requiring movement.

• Fulcrum: The joint around which the movement occurs.

• Effort: The muscular force used to move the object.

• Levers: The bones of the skeleton.

Classes of Levers

• First-Class Lever: The fulcrum is located between the effort and the load.

• Second-Class Lever: The load is located between the fulcrum and the effort.

• Third-Class Lever: The effort is located between the fulcrum and the load.

Planes of Movement and Axes of Rotation

• Movement in the sagittal plane about the frontal axis (e.g., somersaults).

• Movement in the frontal plane about the sagittal axis (e.g., cartwheels).

• Movement in the transverse plane about the vertical axis (e.g., a full twist in trampolining).

Definitions of Planes

• A Sagittal plane is a vertical plane that divides the body into right and left sides.
• The frontal plane is also a vertical plane, but it divides the body into front and back (anterior and posterior) sections.
• The transverse plane is a horizontal plane that divides the body into upper and lower halves.

Definitions of Axes

• The Vertical axis runs through the body vertically from top to bottom.
• The Frontal axis runs through the body horizontally from left to right.
• The Sagittal axis runs through the body horizontally from back to front.

Performance-Enhancing Substances

• Beta Blockers:
  • Effects: Slows heart rate, calms nerves, steadies hands.
  • Side Effects: Can slow heart rate dangerously (potentially leading to cardiac arrest), causes tiredness.
• Anabolic Steroids:
  • Effects: Aids repair of body tissues after stress, promotes muscle growth, reduces fatigue.
  • Side Effects: In females, development of male features; liver and heart damage; high blood pressure; aggression; acne.
• Narcotic Analgesics:
  • Effects: Reduces pain from injuries.
  • Side Effects: Causes nausea and vomiting, addiction, masking of injuries (leading to further damage), loss of concentration.
• Diuretics:
  • Effects: Promotes rapid weight loss.
  • Side Effects: Dehydration, nausea, dizziness, heart and liver failure.
• Stimulants:
  • Effects: Reduces tiredness, increases alertness and endurance.
  • Side Effects: Raises blood pressure, addiction, fatigue rebound, aggression, anxiety, insomnia.
• Peptide Hormones:
  • Effects: Increases red blood cells, increases oxygen-carrying capacity and hemoglobin.
  • Side Effects: Possible blood clots and cardiovascular problems.

Components of Fitness

• Cardiovascular Fitness: The ability to exercise for long periods of time.

• Strength: The amount of force a muscle can exert against a resistance.

• Muscular Endurance: The ability to use voluntary muscles repeatedly without getting tired.

• Flexibility: The range of movement possible at a joint; how far one can stretch or reach.

• Body Composition: The percentage of body weight that is fat, muscle, and bone.

• Speed: How fast one can move.

• Reaction Time: The time between the presentation of a stimulus and the onset of a movement (how quickly one reacts).

• Balance: The ability to maintain the body’s center of mass over its base of support.

• Agility: The ability to change the position of the body quickly and control movement.

• Coordination: The ability to use two or more body parts together smoothly and efficiently.

• Power: The ability to combine strength and speed to perform movements quickly.