Exercise Physiology

Muscular system

This system is mainly concerned with producing movement through muscle contraction. This section explores the different types of muscles in our body and their involvement in sporting activities.

Muscle types

There are three types of muscle in the body:

Involuntary muscles are not under our conscious control which means we can’t make them contract when we think about it.

Voluntary muscles are under our conscious control so we can move these muscles when we want to.

Muscle Fibre Types

There are three two different types of skeletal muscles:

• Slow twitch, also known as type I – oxidative
• Fast twitch, also known as type II – glycolytic

Each type of muscle fibre has different characteristics which are shown in the table:

Muscles front

Muscles back

Muscles and movement

Muscles cause movement by contracting across joints. Muscles are attached to the skeleton by tendons in two places:

• the origin
• the insertion

The origin is the end of a muscle which is attached to a fixed bone. The insertion is the other end of the muscle that is attached to the bone which moves.

Muscular contractions:

Muscles contract in different ways to produce a range of movements:

• Isotonic contraction

  this involves the muscle producing tension and controlling the speed of the muscular contraction. This movement can be a concentric or eccentric muscular contraction.

• Concentric contraction

  this involves the muscle shortening. The origin and insertion of the muscle move closer together and the muscle becomes fatter.

• Eccentric contraction

  this involves the muscle lengthening whilst it is under tension. The origin and the insertion move further away from each other. An eccentric contraction provides the control of a movement on the downward phase and it works to resist the force of gravity.

Muscle pairs

Muscles are attached to bones by tendons. They move our bones and associated body parts by pulling on them – this process is called muscle contraction.

Because muscle contraction cannot push a bone back into its original position, muscles must work together in ‘antagonistic muscle pairs’. One muscle of the pair contracts to move the body part, the other muscle in the pair then contracts to return the body part back to the original position.

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

Key fact: one way to remember which muscle is the agonist – it’s the one that’s in ‘agony’ when you are doing the movement as it is the one that is doing all the work!

For example, when you perform a bicep curl, the bicep will be the agonist as it contracts to produce the movement, while the tricep will be the antagonist as it relaxes to allow the movement to occur.

Antagonistic muscle pairs

The following groups of muscles are antagonistic pairs:

Antagonistic muscle pairs in action

Skeletal system

The skeleton is the central structure of the body and is made up of bones, joints and cartilage. The skeleton provides the framework for muscles and gives the body its defined human shape.

Structure of the skeletal system

The main bones of the skeleton and their location are shown here:

Function of the skeletal system

The skeleton has five main functions:

1. Movement – the skeleton allows movement of the body as a whole and its individual parts. The bones act as levers and also form joints that allow muscles to pull on them and produce joint movements.
2. Support and protection – the bones of the skeleton provide support for the body and also protect the organs found within it. For example, the cranium protects the brain, the ribs offer protection to the heart and lungs, the vertebrae protect the spinal cord and the pelvis offers protection to the sensitive reproductive organs.
3. Production of blood cells – certain bones in the skeleton contain red bone marrow and the bone marrow produces red blood cells, white blood cells and platelets. Examples of bones that contain marrow are the pelvis, sternum, vertebrae and clavicle.
4. Storage of minerals – the bones themselves are made of minerals and act as a mineral store for calcium and phosphorous, which can be given up if the body requires the minerals for other functions.
5. Attachment of muscles – the bones of the skeleton provide surfaces for the attachment of muscles. This is why bones are often irregular shapes and have bony points and grooves to provide attachment points.

Role of joints and connective tissue

• A joint is a place where two or more bones meet and is also called an articulation.
• Connective tissues consist of ligaments, cartilage and tendons.
• A joint is held together by ligaments which give the joints their stability.
• Cartilage is found at the ends of bones and where joints meet.
• Tendons attach muscles to the skeleton.

Synovial joints

These joints allow a wide range of movement and all have a similar joint structure.

• Articular capsule – keeps the contents of the synovial joint in place.
• Synovial membrane – releases synovial fluid into the joint.
• Synovial fluid – a solution which lubricates the joint and allows free movement.
• Articular cartilage – prevents wear and tear on the bones.

Types of synovial joints

Different types of synovial joints allow varying degrees of movement, these include:

1. Hinge – these types of joint can be found in the elbow and knee. Hinge joints are like the hinges on a door, and allow you to move the elbow and knee in only one direction. They allow flexion and extension of a joint.
2. Ball and socket – these types of joint can be found in the shoulder and hip and allow movement in almost every direction. A ball-and-socket joint is made up of a round end of one bone that fits into a small, cup-like area of another bone.
3. Pivot – this joint can be found in the neck, between the top two vertebrae. It allows only rotational movement, such as moving your head from side to side as if you were saying ‘no’

Types of joint movement

The different types of movement that are permitted at each joint are given specific terms.

• Flexion

  Flexion – bending a joint. This occurs when the angle of a joint decreases. For example, the elbow flexes when performing a bicep curl.

• Extension

  Extension – straightening a joint. This occurs when the angle of a joint increases, for example, when throwing a shot put.

• Abduction

  Abduction – movement away from the midline of the body. This occurs in the hip and shoulder joints during a jumping jack movement.

• Adduction

  Adduction – movement towards the midline of the body. This occurs in the hip and shoulder joints, returning the arms and legs back to their original position from a jumping jack movement.

• Circumduction

  Circumduction – this is where the limb moves in a circle. This occurs in the shoulder joint during an overarm tennis serve.

• Rotation

  Rotation – this is where the limb moves in a circular movement around a fixed joint, towards or away from the midline of the body. This occurs in the hip joint in golf, while performing a drive shot.

Muscular-skeletal system

The muscular system works in conjunction with the skeleton to produce movement of the limbs and body.

Ligaments and tendons are two main types of connective tissue that help the muscular-skeletal system produce movements.

Cardiovascular system

The cardiovascular system is made up of three main parts and consists of the heart, the blood vessels and the blood that flows through them.

Structure of the cardiovascular system

If you clench your hand into a fist, this is approximately the same size as your heart. It is located in the middle of the chest, slightly towards the left.

The heart is a large muscular pump and is divided into two halves - the right-hand side and the left-hand side.

The right-hand side of the heart is responsible for pumping deoxygenated blood to the lungs.

The left-hand side pumps oxygenated blood around the body.

Each side of the heart consists of an atrium and a ventricle which are two connected chambers.

The atria (plural of atrium) are where the blood collects when it enters the heart.

The ventricles pump the blood out of the heart, to the lungs or around the body.

The septum separates the right and left-hand side of the heart.

The tricuspid valve is located between the right atrium and right ventricle to prevent backflow of blood from the ventricle to the atrium.

The bicuspid valve is located between the left atrium and left ventricle to prevent backflow of blood from the ventricle to the atrium.

Blood vessels leading into and out of the heart

There are four main blood vessels that take blood into and out of the heart.

The aorta takes blood from the left ventricle to the body.

The vena cava takes blood from the body back to the heart.

The pulmonary artery takes blood from the right ventricle to the lungs.

The pulmonary vein returns blood from the lungs to the left ventricle.

How to remember the facts – it’s a letter game:

arteries = away (from the heart)

The main artery is the aorta

The main vein is the vena cava

Cardiovascular system and exercise

Any changes to heart rate, stroke volume and cardiac output are determined by the intensity and duration of exercise.

Changes to heart rate during exercise

Heart rate is measured in beats per minute (bpm). During exercise the heart rate increases so that sufficient blood is taken to the working muscles to provide them with enough nutrients and oxygen. An increase in heart rate also allows for waste products to be removed.

Maximal heart rate can be worked out by the following equation:

Change to stroke volume during exercise

Stroke volume increases which means more blood is pumped out of the heart every time it contracts.

Changes to cardiac output during exercise

At rest, a person’s cardiac output is approximately 5 litres per minute. During exercise, this can increase to as much as 30 litres per minute as both the heart rate and stroke volume increase.

When taking part in exercise, there is a greater cardiac output because the athlete requires more blood and oxygen to be transported to the working muscles. The increase in the amount of blood also helps with the removal of waste products such as lactic acid and carbon dioxide.

Changes to blood pressure during exercise

A typical blood pressure reading for a person at the start of exercise would be around 160/85 mmHg.

Respiratory system

The main role of the respiratory system is to transport oxygen from the air that we breathe through a system of tubes into our lungs and then into the blood stream.

Structure of the respiratory system

Passage of air into the lungs

1. Air enters the body and is warmed as it travels through the mouth and nose.
2. It then enters the trachea.
3. The air then passes into one of two bronchi. One bronchus enters each lung.
4. Air then travels into bronchioles.
5. At the end of the bronchioles, the air enters one of the many millions of alveoli.

Gaseous Exchange

Gaseous exchange occurs in the alveoli in the lungs and takes place by diffusion.

Diffusion is the movement of gas from an area of high concentration to an area of low concentration.

In the alveoli, there is a high concentration of oxygen and in the bloodstream, there is a high concentration of carbon dioxide.

Oxygen diffuses into the blood from the alveoli and carbon dioxide diffuses into the alveoli from the blood.

At the muscle, the opposite occurs and carbon dioxide enters the blood from the muscle and oxygen enters the muscles.

Capillaries surround the alveoli in the lungs. Both the capillaries and alveoli walls are very thin – just one cell thick. They are made of semi-permeable membranes which allow oxygen and carbon dioxide to pass through them.

Lung volumes

Vital capacity is the maximum amount of air that can be breathed out after breathing in as much air as possible. Taking part in regular aerobic exercise has been shown to increase a person’s vital capacity.

Breathing rate (frequency) is the number of breathes in a minute. The average breathing rate is 12 breaths/minute.

Tidal volume is the amount of air breathed in with each normal breath. The average tidal volume is 0.5 litres (500 ml).

Minute ventilation (VE) is the total volume of air entering the lungs in a minute. The average minute ventilation is 6 litres/minute.

During exercise, tidal volume increases as the depth of breathing increases and the rate of breathing increases too. This has the effect of taking more oxygen into the body and removing more carbon dioxide.

Cardiorespiratory system

The cardiorespiratory system works together to get oxygen to the working muscles and remove carbon dioxide.

During exercise, the muscles need more oxygen in order to contract and they produce more carbon dioxide as a waste product. To meet this increased demand by the muscles, the following happens:

Breathing depth (tidal volume) and rate increase – this gets more oxygen into the lungs and removes more carbon dioxide out of the lungs.

The graph shows that as a person goes from rest to exercise, their tidal volume increases.

Heart rate increases – this increases the rate that oxygen is transported from the blood to the working muscles and carbon dioxide is transported from the working muscles to the lungs.

This graph shows that:

• at rest, the person’s heart rate is around 60 bpm
• at 8 minutes, just before taking part in exercise, their heart rate increases – this is called the anticipatory increase in heart rate which occurs when a person starts to think about taking part in exercise
• at 10 minutes, the person starts to take part in exercise and there is a steep increase in heart rate, up to 145 bpm at 13 minutes
• the heart rate remains high during exercise
• when the person stops taking part in exercise, the heart rate decreases

Aerobic and anaerobic exercise

Depending upon whether the body uses oxygen or not in order to perform specific exercises determines if the exercise is aerobic (with oxygen) or anaerobic (without oxygen).

Anaerobic respiratory system

The anaerobic respiratory system supplies energy very quickly for sports such as vaulting in gymnastics or throwing a javelin where the activity only lasts a few seconds.

There are two types of anaerobic energy systems. These are:

1. the creatine phosphate anaerobic system
2. the lactic acid anaerobic system

The creatine phosphate (CP) anaerobic system supplies energy faster than all other energy systems.

It is used for explosive, high-intensity contractions, such as in sprinting 100 metres, but it can only supply energy for about ten seconds.

Once the CP system has run out, the lactic acid system is used to supply energy.

This system breaks down glucose into lactic acid. It produces energy very quickly, but not as quickly as the CP system.

The lactic acid energy system produces the majority of the energy for moderate to high intensity activities such as running 400 metres.

Energy balance equation

The aerobic respiratory system is responsible for producing the majority of our energy while our bodies are at rest or taking part in low-intensity exercise for long periods of time, such as jogging or long-distance cycling.

Short and long-term effects of exercise

When a person takes part in exercise, their body systems provide energy for these activities. After regular exercise participation, these systems adapt to improve exercise performance.

Short-term effects of exercise on the body systems

When a person takes part in exercise the cardiovascular, respiratory, energy and muscular systems all work together to supply energy to the working muscles and remove waste products.

After exercising, the muscles need to rest, adapt and recover. There is a risk of injury if the body is not rested for long enough after exercise.

Long-term effects of exercise on the body systems

Taking part in regular exercise, around 3 times per week for 6 weeks, will lead to adaptation of the body systems that are trained. This has the effect of increasing performance in that type of exercise or sport.

Cardiac hypertrophy

The muscle wall of the left ventricle increases in size so is able to pump out more blood during each beat which increases the stroke volume. As the stroke volume is increased, the resting heart rate decreases but cardiac output (Q) remains the same as SV × HR = Q.

Capillarisation is the process where new capillaries are formed. Capillarisation takes place at the alveoli in the lungs and in skeletal muscle. This has the effect of increasing the amount of oxygen that can be transferred to the working muscles as well as increasing the amount of carbon dioxide that can be removed.