ACSM CPT Chapter 5: Exercise Physiology

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Chapter Objectives: 

• Give the fundamental background regarding the biological function of the human body.
• Learn the physiological mechanism of the body systems and their relation to exercise.
• Find key elements of the body’s reaction and adaptations to stimuli for the effective prescription of exercise training.

Definition of Exercise Physiology

This is the study of the body systems and their reaction that they have to stress from exercise. It looks at exercises’ effects on the cardio, respiratory, muscular, skeletal, and nervous systems. We will look at both the acute and the chronic effects that occur.

Cardiovascular System

This deals with how both nutrients and oxygen are transported in the cardiovascular system throughout the body and specifically into the muscles that are working.

These are the specific functions of the cardiovascular system:

• Deoxygenated blood is transported from the lungs to the heart.
• Oxygenated blood is transported from the heart to the tissues and tissues to the heart.
• Nutrients are distributed among the body’s cells.
• Remove metabolic wastes from working cells for both elimination and reusal.
• Regulates PH for the control of acid-base balance.
• Transport hormones and enzymes for the regulation of physiological function.
• Maintain fluid balances.
• Maintain body temperature by the distribution of heat.

Heart

Our heart has four chambers that are used as reservoirs and pumps. The two upper ones are the atria, and the lower are the ventricles.

Tissue Coverings and the Layers of the Heart

It is covered by the pericardium, which has a fibrous and a serous layer. It helps the heart to anchor in the chest and keep its position. The thickest cardiac muscle layer is called the myocardium. 

Chambers, Valves, and Blood Flow

The flow with the chambers and valves follows this path:

• Blood that is deoxygenated flows to the right atrium from the superior and inferior vena cava, the coronary sinus, and the anterior cardiac veins.
• The RA contracts,  and the blood moves to the tricuspid valve and then to the right ventricle.
• The right ventricle then contracts, causing the tricuspid valve to close, and blood to flow into the pulmonic valve and then the pulmonary arteries and branches of the pulmonary system.
• The blood enters the alveolar capillaries coming from the pulmonary arteries. This is where the exchange of gases occurs. The oxygen is absorbed, and the CO2 is taken out.
• The blood then flows back into the left atrium from the pulmonary veins.
• This left atrium contracts and the blood then flows into the mitral valves and then into the left ventricle.
• The left ventricle contracts, causing the mitral valve t close, and then the blood goes to the aortic valve and then the aorta and its branches to distribute to the heart and the whole body.

The Blood Vessels

When the blood exits the heart, it enters what we call the vascular system. This is a large amount of blood vessels that will deliver the blood to the tissues and promotes the delivery of nutrients and oxygen. Here there will be the exchange of metabolic wastes, hormones, and other cell products. 

Cardiac Function

Heart Rate

This is the number of times that the heart beats in a minute. The average normal resting rate is between 60 and 80.

Fitter people have a lower resting heart rate due to their higher stroke volume.

Blood pressure

This is a product of the amount of blood that is pumped from the heart and the flow resistance within the vessel.

Systolic blood pressure is the pressure on the arterial walls when the ventricle contraction phase occurs. This is the top number.

Diastolic blood pressure is the pressure on the arteries when the ventricles are relaxed. This is a low number.

The average blood pressure is 120 / 80 mmHg.

Stroke Volume

This is the amount of blood coming from the left ventricle during one contraction.

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Cardiac Output

This is the volume of blood that is pumped by the heart per minute and it is measured in liters. The cardiac output is the product of heart rate and stroke volume.

Acute Responses to Cardiovascular Exercise

Heart Rate

The normal heart rate response in an acute exercise session is a simple linear increase alongside exercise intensity and oxygen uptake.

Stroke Volume

Stroke volume has a curvilinear increase with intensity until it reaches the near max levels of 40 – 50% of max aerobic capacity.

Cardiac Output

This increases linearly with increases in exercise intensity. The max levels depend on factors like age, posture, size of the body, and the presence of diseases.

Arteriovenous Oxygen Difference

This is the amount of oxygen taken by tissues and shows the difference between the content of oxygen of the arterial blood and the oxygen content of the venous blood. In times of vigorous exercise, active muscles take greater levels of oxygen from arterial blood and reduce the oxygen content in the venous blood.

Blood Flow

When exercising blood flow is increased to the areas and muscle that need it, much like what happens during digestion.

Blood Pressure

Systolic blood pressure increases linearly with exercise intensity and maxes out at 190 – 220 mmHg. 

Maximal Oxygen Consumption

This is known as VO2 max. It is the widely accepted measure of cardio endurance. It is defined as the highest amount of oxygen transport that can be achieved during maximal physical exertion.

Respiratory System

This system is responsible for the filtration of the air that goes into the body and it makes gas exchange possible in the alveoli.

Control of Breathing

The muscles of the respiratory system do not have the ability to regulate their contractions, and so they are actually controlled by the brainstem and respiratory pathways.

Distribution of Ventilation

Upper respiratory tract

This is the pathways for air to go into the lower tract. This comprises the nose, sinus, larynx, and pharynx.

Lower respiratory tract

This starts in the trachea and it also includes the bronchi, bronchioles, and the alveoli.

Ventilatory Pump

This is the mechanisms used to breathe and includes the chest wall, respiratory muscles, and the pleural space.

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Chest Wall

This includes the muscles used for ventilation, and the bones in the area, the spine, ribs, and sternum. 

Ventilatory Muscles

The muscles that are used for respiration are the only ones essential to life. The diaphragm is a main muscle for inspiration and any injury above the 3 – 5^th vertebrae will compromise the ventilation. Other important muscles are the internal intercostals and the abdominal muscles.

Distribution of Blood Flow

The lungs will receive blood from the pulmonary arteries and then essentially exchange the oxygen that the lungs get and the carbon dioxide from the blood that was returned, and the exchange of gases is complete when we exhale the CO2.

Pulmonary Ventilation

This is the air volume that is exchanged within a minute. For an average man, 6 liters per minute is the average at rest. When maximally exercising, it can be as much as 15 – 25 times the resting amount.

Ventilatory Changes

People that are trained have larger lung volumes and capacities for diffusion at both rest and during exercise. Ventilation, however, is moderately unchanged by cardio training.

Energy Systems

Energy is needed for the production of mechanical work, the ability to balance body temperature, and the fulfillment of the biological and chemical activities that take place within the body.

Aerobic and Anaerobic Metabolism

When going from rest to max exertion, the requirements for energy by the muscles doing the work are substantial. Thus, the need for resynthesis of ATP is important.

Anaerobic Metabolism

Adenosine Triphosphate

ATP is the ideal agent of energy transfer that is used to power all of the cell’s energy needs. Energy is released during the hydrolysis of ATP to form ADP and one phosphate. This is the process that powers skeletal muscle contractions.

Creatine Phosphate

This CP system transfers high energy phosphates of creatine phosphate for ATP to be rephosphorylated. This is a rapid system due to their only being one step, but there are very limited quantities of creatine stored in cells. There is essentially only enough for 5 – 10 seconds of activity at a time. Since oxygen isn’t involved, this is called anaerobic.

Anaerobic Glycolysis

This is the rapid breakdown of carbs, both glycogen and glucose, when oxygen is not present. Lactate is a product of anaerobic glycolysis which may also be used to resynthesize ATP.

Aerobic Oxidation

This combines two different processes: the Krebs cycle and the electron transport chain. This has the ability to use fats, proteins, and carbs to produce ATP. This, due to the name, obviously requires the use of oxygen for the process to be completed. 

Oxygen Requirement: Beginning of Exercise and in Recovery

Oxygen deficit

This is the lag in the consumption of oxygen that happens at the beginning of oxygen. For the first stage from rest to Submax exercise, oxygen consumption builds gradually. It reaches an optimal level for supporting the energy demand for the exercise, also called the steady state. So, all in all, this is the difference between the required amount of oxygen and the actual oxygen consumed.

Excess Postexercise Oxygen Consumption

This is the consumption of more than normal amounts of oxygen following exercise. The levels of oxygen uptake remain elevated at levels higher than rest for minutes after exercise.

Muscular System

Skeletal muscles

These are the voluntary muscles that people have control over. These are also striated. 

Each muscle comprises many different numbers of muscle bundles that we call fasciculi. These fasciculi are covered and separated by perimysium. Each muscle fiber is covered by the endomysium. The epimysium covers the whole muscle and is contiguous with the tendons of the muscle.

Muscle Contraction

The sarcomere is the smallest contractile unit of muscle cells. It is made up of two muscle proteins: myosin and actin. Actin has troponin and tropomyosin. Myosin has cross bridges where the actin attaches. 

The sliding filament is what describes the events that happen with actin and myosin filaments in the contraction and relaxation of muscles. Nerve impulses are received, and the cross bridges in myosin pull the actin toward the center of the sarcomere, thus creating tension. This shortens the sarcomere and the entire muscle. The muscle cell will maximally contract, or not contract at all. This is always how it works. We call this the all or none principle. The force produced is determined by the number of motor units recruited. 

Muscle Contraction and Training

Muscles stay at a constant length during static contractions. These are also called isometric exercises.

Functional strength is known as work done against resistance that shows benefits toward doing activities of daily life or sports.

Concentric actions are when the muscle contracts and shortens, while eccentric ones are when the muscle lengthens.

Muscle Fiber Types

Slow twitch muscle fibers

These fibers are the ones that are resistant to fatigue. They are present in sports that require a lot of endurance. These muscles work in lo intensities more often and they are usually the smaller fibers.

Fast twitch muscle fibers

These fibers have better success than he slow twitch ones in power and high intensity activities. These fibers are capable of becoming larger than what the slow twitch ones are.

Neuromuscular Activation

Motor unit activation

A motor unit is made up of a motor neuron and all of the fibers that it innervates. These range in size from just a few to a many as several hundred fibers.

Skeletal System

Along with the protection of vital organs and storage for nutrients and blood constituents, the skeletal system is also used for movement and locomotion.

Structure and Function of Joints in Movement

Joints determine the effective interaction of bones and muscles. 

Proprioception is the receiving of information regarding the movement and positioning of the body and its parts.

The degree of movement that a joint has is known as the range of motion, and this can be active and passive, as we talked about in previous chapters.

Neurological System

Central Nervous System

The brain is the most important portion of the central nervous system, and it is surrounded by our skull to protect it. The spinal cord extends from the brain and is protected by the vertebral column. 

The central nervous system is where all sensory stimuli is received, integrated, analyzed, interpreted, and then relayed as impulses of the nerves to the glands and muscles for action to take place. 

Peripheral Nervous System

This is made up of the cranial and spinal nerves that are associated with the spinal cord and the nerve cell bodies that we call ganglia. These nerves are responsible for carrying information to the central nervous system.

Autonomic Nervous System

This system is used to regulate the visceral activities. These include things like hormone secretion, breathing, heart rate, and digestion. 

Neuromuscular Control

The size principle: motor units are recruited in their order according to the recruitment thresholds and the firing rates they have. This shows that most muscles contain a range of motor units slow and fast and the progression is from type I to type IIx in terms of recruitment.

Muscle Spindle and Golgi Tendon Organs

These are special sensory receptors that are in the muscles and tendons. They are sensitive to stretch, pressure, and tension. We also call these proprioceptors as they help with the proprioception mentioned above. 

A feature that muscle spindles help with is the stretch reflex. This reflex occurs when there is a stretch in the muscle and the body sends a signal to correct it and contracts the muscle. This can be used for an advantage in training. 

The Golgi tendons have a similar feature where they are used for detecting tension differences and send reflex inhibition signals to prevent contraction. 

Exercise System Adaptations: Strength, Cardiovascular

Resistance Training

This is effective in the improvement of strength and endurance for our muscles. 

We use the overload principle to continue to make changes as our body adapts to the training. 

Hypertrophy is the increase in size that occurs in muscles and is seen with regular resistance training.

A lot of the strength gains that happen initially are due to changes that happen in the nervous system that make our movements more efficient.

Cardiovascular Exercise

Endurance exercise training increases our functional capacity and gives relief from CAD for some people.

Aerobic capacity increases by around 20 percent for most people with regular training. 

Myocardial demands when at rest and work are decreased.

Overall Changes

• Resting heart rate decreases by about 10 – 15 beats per minute with cardio training. 
• The stroke volume increases at rest and most points during exercise.
• Both blood pressure levels may decrease. 
• Less lactic acid is produced at Submax levels.