B. Physiology Of Exercise I B

B. PHYSIOLOGY OF EXERCISE

B1. MUSCLES AND MOVEMENT

ANATOMY OF THE SKELETON

The skeleton provides a strong framework that holds your body up and maintains its shape

The skeleton also protects soft organs and provides attachment sites for your muscles

Cartilage, a type of connective tissue that is softer than bone and provides cushion between bones in a joint.

HOW MOVEMENT IS POSSIBLE Movement is a complex coordination of

several parts of your body acting together, each with a specific role:

TISSUE ROLE

BONES Provide anchorage for muscles. Act as levers. Provide support

MUSCLES As a muscle contracts, it pulls on the attached bone. Since muscles can only pull, an opposing motion is needed to restore to bone’s original position.

TENDONS Tough and dense connective tissue between muscle and bone. Transmit the force generated by a muscle contraction.

LIGAMENTS Strong connective tissue that holds the bones in joints in their place.

NERVES Transmit electrical signals to produce muscle contractions and coordinate movement.

STRUCTURE OF A LONG BONE

JOINTS An area where one bone

meets another bone is called a joint.

Immovable joints: connect bones in a way that allows little or no movement. Like the ribs attached to the vertebrae.

Movable joints: allow you to bend, twist, and rotate your limbs, neck, and torso. The bones in a movable joint are held together by a strong, fibrous connective tissue called a ligament.

HUMAN ELBOW JOINT

A. Humerus (upper arm) bone.

B. Synovial membrane that encloses the joint capsule and produces synovial fluid.

C. Synovial fluid (reduces friction and absorbs pressure).

D. Ulna (radius) the levers in the flexion and extension of the arm.

E. Cartilage (red) living tissue that reduces the friction at joints.

F. Ligaments that connect bone to bone and produce stability at the joint.

MOVEMENT OF THE HIP AND THE KNEE

Knee Joint: The knee joint is an

example of a hinge joint. The pivot is the knee joint. The lever is the tibia and

fibula of the lower leg. A knee extension is

powered by the quadriceps muscles.

A knee flexion is powered by the hamstring muscles.

Movement is one plane only.

Watch movement of knee joint: http://www.youtube.com/watch?v=wyiJw034ssA

The Hip Joint: Rotation is in all planes and axis of movement. The lever is the femur and the fulcrum is the hip joint. The effort is provided by the muscles of quadriceps, hamstring and

gluteus. The shoulder is a ball and socket joint. The humerus is the lever. The shoulder (scapula and clavicle) form the pivot joint. Force is provided by the deltoids, trapezius and pectorals. Movement is in all planes.

Watch movement of hip joint: http://www.youtube.com/watch?v=sPsyPwYZb6A&feature=related

Antagonistic muscle pairs: Muscles must work in pairs. For each skeletal muscle that is contracting, there is an opposing muscle—one that is relaxed but that can contract and pull the bone back in the opposite direction.

• One muscles bends the limb at the joint (flexor) which in the elbow is the biceps.

• One muscles straightens the limb at the joint (extensor) which in the elbow is the triceps.

A flexion like this one is called a concentric contraction

STRUCTURE OF A MUSCLE Taking a closer look, a skeletal muscle such as your

calf muscle consists of bundles of parallel muscle fibers along with a supply of nerves and blood vessels.

STRUCTURE OF A MUSCLE A muscle fiber is a single long cylindrical

muscle cell that contains many nuclei.

Inside a muscle fiber are bundles of smaller units called myofibrils.

Each myofibril has alternating light and dark bands: striated muscle

SARCOMEREEach sarcomere is composed of two kinds of filaments, thin filaments are composed of the protein actin. The thick filaments are composed of the protein myosin and have myosin crossbridges.

1. In each mini-contraction, myosin crossbridges first bind to thin filaments. 2. Next, the crossbridges bend, pulling the thin filaments toward the center of the sarcomere. 3. ATP then binds to each crossbridge, releasing it from the thin filament. 4. The crossbridge is now free to attach at a new spot and further pull the thin filament along

Watch muscle contraction: http://www.youtube.com/watch?v=83yNoEJyP6g

MECHANISM OF A MUSCLE CONTRACTION

1. An action potential arrives at the end of a motor neuron, at the neuromuscular junction.

2. This causes the release of the neurotransmitter acetylcholine. 3. This initiates an action potential in the muscle cell membrane. 4. This action potential is carried quickly throughout the large

muscle cell by invaginations in the cell membrane called T-tubules. 5. The action potential causes the sarcoplasmic reticulum (large

membrane vesicles) to release its store of calcium into the myofibrils.

6. Myosin filaments have cross bridge lateral extensions. 7. Cross bridges include an ATPase which can oxidize ATP and

release energy. 8. The cross bridges can link across to the parallel actin filaments. 9. Actin polymer is associated with tropomyosin that occupies the

binding sites to which myosin binds in a contraction. 10. When relaxed the tropomyosin sits on the outside of the actin

blocking the binding sites. 11. Myosin cannot cross bridges with actin until the tropomyosin

moves into the groove. 12. The calcium binds to troponin on the thin filament, which

changes shape, moving tropomyosin into the groove in the process. 13. Myosin cross bridges can now attach and the cross bridge cycle

can take place.

Cross Bridge Cycle:

1. The cross bridge swings out from the thick filament and attaches to the thin filament.

2. The cross bridge changes shape and rotates through 45°, causing the filaments to slide. The energy from ATP splitting is used for this “power stroke” step, and the products (ADP + Pi) are released.

3. A new ATP molecule binds to myosin and the cross bridge detaches from the thin filament.

4. The cross bridge changes back to its original shape, while detached (so as not to push the filaments back again). It is now ready to start a new cycle, but further along the thin filament.

ELECTRON MICROGRAPH OF A MYOFIBRIL

Note that the filaments themselves don't get shorter, but as they slide across one another, their overlap increases. The sarcomere shortens (distance between Z-lines is smaller). The process can continue until the sarcomere is fully contracted. As the sarcomeres of many muscle fibers shorten together, the entire muscle contracts.

If electron micrographs of a relaxed and contracted myofibril are compared it can be seen that:

PRACTICE: TRANSVERSE SECTION OF A STRIATED MUSCLE

1.Explain the difference between a transverse and a longitudinal section of a muscle.

2. Deduce what part of the myofibril is represented by the drawings as small dots.

3. Explain the differences between the diagrams in the pattern of dots.

Actin only Myosin only

Overlap of actin and myosin during muscle contraction

Muscle contraction: http://www.youtube.com/watch?v=83yNoEJyP6g

Krebs cycle: http://

www.youtube.com/watch?v=WcRm3MB3OKw

B2. TRAINING AND THE PULMONARY

SYSTEM

BREATHING

Breathing is not the same as respiration.

When we breathe we exchange gases (O2 and CO2) with the environment

Respiration occurs at a cellular level

DEFINITIONS Total lung capacity: volume of air in the

lungs after a maximum inhalation. Vital capacity: maximum volume of air

that can be exhaled after a maximum inhalation.

Tidal volume: volume of air taken in or out with each inhalation or exhalation.

Ventilation rate: number of inhalations or exhalations per minute (this term is used, not breathing rate).

Any physical activity involves muscle contraction, which requires energy in the form of ATP.

ATP can be supplied by aerobic cell respiration

Concentration gradients in the lungs have to be maintained to ensure correct oxygen and carbon dioxide diffusion and exchange

AEROBIC CELL RESPIRATION If oxygen is available to a cell, pyruvate produced by

glycolysis can be oxidized to release more energy. Energy released from pyruvate oxidation is used to

produce ATP. Oxidation of pyruvate also involves the production of

CO2 and water. Watch the Krebs cycle:http://www.youtube.com/watch?v=WcRm3MB3OKw

GAS EXCHANGE IN THE ALVEOLI Oxygen diffuses into the body across the

gas exchange surface in the alveoli, and carbon dioxide diffuses out.

During gentle to moderate exercise, gases exchange rapidly and O2 and CO2 concentration inside the body are restored.

TIDAL VOLUME AND VENTILATION RATE DURING EXERCISE If the intensity of exercise increases, the

rate at which gas diffusion on the alveoli surface occurs must also increase.

If blood moves quicker to the lungs, CO2 can be released quicker.

It is also essential to bring more O2 from the air outside.

By breathing faster (increased ventilation rate) and also deeper (increased tidal volume) more air is present inside the lungs for gas exchange.

TRAINING AND THE PULMONARY SYSTEM Training is a program of exercise designed to

develop a particular type of fitness and to improve performance. By training, the pulmonary system is affected:

The ventilation rate at rest can be reduced by 10 - 15% (from about 14 to 12 bpm), because the efficiency of gas exchange is increased

The maximum ventilation rate can be increased from about 40 to 45 bpm or more, due to the strengthening of the diaphragm and the intercostal muscles.

Vital capacity may increase slightly (about 5%)

B3. TRAINING AND THE CARDIOVASCULAR SYSTEM

DEFINITIONS Heart rate: number of contractions of

the heart per minute. Stroke volume: volume of blood pumped

out with each contraction of the heart. Cardiac output: volume of blood

pumped out by the heart per minute. Venous return: volume of blood

returning to the heart via the veins per minute.

Explain the changes in cardiac output and venous return during exercise.

When the body’s overall cell respiration rate rises (to produce more energy), for example during exercise, the CO2 content of the blood rises.

Receptor cells detect a lowered blood pH (because of a high CO2 concentration) and causes impulses to be sent by the brain to the pacemaker, increasing cardiac output (because heart rate and stroke volume increase).

Many veins are located between or adjacent to muscles that are used during exercise.

Contraction of muscles used during exercise squeezes blood in adjacent veins, increasing blood pressure and flow rate, therefore increasing venous return. Valves in veins ensure that blood only flows in one direction.

Compare the distribution of blood flow at rest and during exercise:

Blood flow to the brain is unchanged during exercise.

Blood flow to the skin is increased for temperature regulation.

Blood flow to the heart wall, and skeletal muscles is increased.

Blood flow to the kidneys, stomach, intestines and other abdominal organs is reduced, as their functions can be reduced during periods of exercise.

EXPLAIN THE EFFECTS OF TRAINING ON HEART RATE AND STROKE VOLUME, BOTH AT REST AND DURING EXERCISE:

Training can make the heart bigger: thicker ventricle walls (stronger contractions that can squeeze out more blood) and larger ventricular volumes (more blood fits inside the heart to be pumped out). Therefore more blood can be pumped out with each heartbeat = maximum stroke rate is higher.

Training does not significantly affect the maximum heart rate, but the maximum cardiac output is greater.

This means muscle contractions can be more frequent and more powerful.

AT REST DURING EXERCISE

Cardiac output is not significantly altered

Increase in stroke volume, therefore more blood can be supplied with fewer heartbeats.

Lower resting heart rate Lower exercising heart rate

Intensity of exercise can be increased. The trained athlete can run, swim or cycle faster.

THE EFFECTS OF TRAINING …

Evaluate the risks and benefits of using EPO (erythropoietin) and blood transfusions to improve performance in sports:

There are clear ethical issues involved in the use of performance-enhancing drugs.

Human blood varies in the relative amounts of cells and plasma.

The higher the cell volume, the greater the oxygen-carrying capacity of the blood, allowing more intense exercise to be sustained by aerobic cell respiration.

Erythropoietin (EPO) is a hormone that stimulates the production of red blood cells.

Another method is to transfuse blood shortly before the event.

Benefit: Increase performance during events

involving intense exercise (100m race, swimming, etc.)

Risk:Significant increases in the risk of strokes

and heart attacks as a result of blood clot formation (cardiac arrest during sleep)

B4. EXERCISE AND RESPIRATION

DEFINITIONS VO2 : the volume of oxygen that is absorbed by

the body per minute and supplied to the tissues. VO2 max : the maximum rate at which oxygen can

be absorbed by the body and supplied to the tissues.

Aerobic cell respiration can only occur if oxygen is available.

If the intensity of exercise increases, the pulmonary system absorbs more oxygen and the cardiovascular system transports the increased amounts.

If the intensity of exercise continues to rise, we reach VO2 max and the rate of oxygen supply is less than the rate of use.

Outline the roles of glycogen and myoglobin in muscle fibres.

Myoglobin is used to store oxygen in some muscle fibers.

Each molecule of myoglobin can store one molecule of oxygen.

Myoglobin releases oxygen during periods of intense exercise to allow aerobic respiration to fuel ATP production for a little longer.

After the oxygen stored in myoglobin is used up, aerobic cell respiration can only happen as quickly as oxygen is supplied by the heart and lungs.

All muscles are composed of specialized muscle fibers. Muscle fibers have certain key physical distinctions that create two distinct kinds of fibers, fast-twitch (type II fibers) and slow-twitch (type I fibers).

Whether a muscle fiber functions as a fast-twitch or slow-twitch fiber is subject to a number of physical and neurological factors.

Slow-twitch fibers are governed by slow conduction neurons, the relay switch of the nervous system that governs a group of muscle fibers ranging in size from as few as 10 to as many as 2,000 fibers.

Fast-twitch fibers are governed by fast-acting neurons, which are capable of transmitting or firing the nerve impulses that command movements by the muscle 10 times more frequently than the slow-twitch neurons will fire.

Fast-twitch fibers store glycogen within the cells of the muscle fiber.

Glycogen, the storage form of glucose, is then utilized at the muscle in the cycle of electrochemical reactions that produce ATP, the source of energy within the muscle.

The muscles store glycogen in quantities that total approximately 1% of the muscle mass, a reserve that is quickly depleted through intense exercise; for an approximate maximum of 90 seconds.

Anaerobic cell respiration is used to provide ATP in muscles during high-intesity exercise when oxygen cannot be supplied rapidly enough for aerobic cell respiration.

Only glucose can be used as a substrate and lactate is produced.

Lactate accumulates in muscles and blood and the body can only tolerate a limited amount, so anaerobic cell respiration can only be used for short periods of intense exercise.

Outline the method of ATP production used by muscle fibres during exercise of varying intensity and duration:

Creatine phosphate can be used to regenerate ATP for 8–10 seconds of intense exercise. Beyond 10 seconds, ATP is produced entirely by cell respiration.

As the intensity of exercise decreases and the duration increases, the percentage of anaerobic cell respiration decreases and aerobic cell respiration increases.

Evaluate the effectiveness of dietary supplements containing creatine phosphate in enhancing performance:creatine phosphate + ADP creatine + ATP

Creatine phosphate is absorbed in the intestines, but the concentration of creatine phosphate in the muscles only increases by a small amount.

There is some evidence of an increase in the maximum intensity of exercise over short time periods, but performance in endurance events is not improved.

There is some evidence of creatine phosphate causing increased fluid retention, which would increase body mass and decrease athletic performance.

Outline the relationship between the intensity of exercise, VO2 and the proportions of carbohydrate and fat used in respiration.

As the intensity of exercise increases, VO2 rises until it reaches VO2 max. Use of fat in respiration falls and use of carbohydrate rises until it reaches 100%.

State that lactate produced by anaerobic cell respiration is passed to the liver and creates an oxygen debt.

Outline how oxygen debt is repaid. Lactate is turned into pyruvate, which is

converted to glucose or used in aerobic respiration in the mitochondrion, using oxygen taken in during deep ventilations after exercise.

B5. FITNESS AND TRAINING

Define fitness.

Discuss speed and stamina as measures of fitness.

Distinguish between fast and slow muscle fibres.

Fast muscle fibres (typical of sprinters) have greater oxygen needs, low myoglobin levels and provide a maximum work rate over shorter periods (strength).

Slow muscle fibres (typical of marathon athletes) have a very good blood supply, plenty of myoglobin and are capable of sustained activity (stamina) and high rates of aerobic respiration.

Distinguish between the effects of moderate-intensity and high-intensity exercise on fast and slow muscle fibres.

Moderate-intensity exercise stimulates the development of slow muscle fibres. High-intensity exercise stimulates the development of fast muscle fibres.

Discuss the ethics of using performance-enhancing substances, including anabolic steroids.

B6. INJURIES

Discuss the need for warm-up routines. TOK: There is almost universal belief in

the need for warm-up and sometimes also warm-down routines, but much of the evidence for these theories is at best anecdotal and at worst non-existent. The difficulty of conducting controlled trials without a placebo effect could be discussed. The willingness of athletes to believe what they are told, without questioning it, could also be considered.

Describe injuries to muscles and joints, including sprains, torn muscles, torn ligaments, dislocation of joints and intervertebral disc damage.