Exercise Physiology Free Response
Terms in this set (29)
Describe the mechanisms involved in inspiration and expiration.
Inspiration is an active process in which the diaphragm and the external intercostal muscles contract, increasing the dimensions, and thus the volume, of the thoracic cage. This decreases the pressure in the lungs, causing air to flow in.
Expiration at rest is normally a passive process. The inspiratory muscles and diaphragm relax and elastic tissue of the lungs recoils, returning the thoracic cage to its smaller, normal dimensions. This increases the pressure in the lungs and forces air out.
Forced or labored inspiration and expiration are active processes and involve accessory muscle actions.
What is a spirometer? Describe and define the lung volumes measured using spirometry.
A spirometer measures the volumes of air inspired and expired and therefore changes in lung volume. A simple spirometer contains a bell filled with air that is partially submerged in water. A tube runs from the subject's mouth under the water and emerges inside the bell, just above the water level. As the person exhales, air flows down the tube and into the bell, causing the bell to rise.
Tidal volume: the amount of air entering and leaving the lungs with each breath.
Vital Capacity: the greatest amount of air that can be expired after maximal inspiration.
Residual volume: the amount of air remaining in the lungs after a maximal expiration (some air remains in lungs after full expiration)-> cannot be measured with spirometry
Total lung capacity: sum of the VC and RV
How are oxygen and carbon dioxide transported in the blood?
Oxygen is transported in the blood either 1) combined with hemoglobin in the red blood cells (greater than 98%) or 2) dissolved in blood plasma (less than 2%). Only about 3ml of oxygen is dissolved in each liter of plasma. Hemoglobin allows the blood to transport nearly 70x more oxygen than can be dissolved in plasma.
Carbon dioxide is carried in the blood primarily in 3 forms: as bicarbonate ions resulting from the dissociation of carbonic acid, dissolved in plasma, and bound to hemoglobin (called carbaminohemoglobin). The majority is carried in the form of bicarbonate, about 60-70%. 7-10% is dissolved in plasma.
How is oxygen unloaded from the arterial blood to the muscle and carbon dioxide removed from the muscle into the venous blood?
Oxygen is unloaded from the arterial blood to the muscle in the form of hemoglobin. Hemoglobin loses its oxygen to the tissues, causing it to be less saturated and oxygen to enter the muscle. With exercise, the ability to unload oxygen to the muscles increases as the muscle pH decreases.
Carbon dioxide exits the cells by simple diffusion in response to partial pressure gradient between the tissue and capillary blood.
Describe how pulmonary ventilation is regulated. What are the chemical stimuli that control the depth and rate of breathing? How do they control respiration during exercise?
The respiratory muscles are under the direct control of motor neurons, which are in turn regulated by respiratory centers (inspiratory and expiratory) located within the brain stem (in the medulla oblongata and pons). These centers establish rate and depth of breathing by sending out periodic impulses to the respiratory muscles. The central chemoreceptors in the brain are stimulated by an increase in H+ ions in the cerebrospinal fluid. The carotid chemoreceptors are more sensitive to changes in H+ concentration and PCO2, and PCO2 appears to be the strongest stimulus for the rate of breathing.
The goal of respiration is to maintain appropriate levels the blood and tissue gases and to maintain proper pH for normal cellular function.
Describe how heart rate, stroke volume, and cardiac output respond to increasing rates of work. Illustrate how these three variables are interrelated.
HR increases directly in proportion to the increase in exercise intensity (increasing rates of work) until near-maximal exercise is achieved. As maximal exercise intensity is approached, HR begins to plateau even as the exercise workload continues to increase, indicating maximum HR.
SV increases with increasing exercise intensity up to intensities somewhere between 40% and 60% of VO2(max). At that point, SV typically plateaus, remaining essentially unchanged up to and including the point of exhaustion.
Since cardiac output is the product of heart rate and stroke volume (Q= HR x SV), cardiac output predictably increases with exercise intensity
How does blood pressure respond to exercise?
During endurance exercise, systolic blood pressure increases in direct proportion to the increase in exercise intensity. However, diastolic pressure does not change significantly and may even decrease. Increased systolic blood pressure results from the increased cardiac output that accompanies increasing rates of work. This increase in pressure helps facilitate the increase in blood flow through the vasculature.
What is cardiovascular drift? What two theories have been proposed to explain this phenomenon?
With prolonged aerobic exercise or aerobic exercise in a hot environment at a steady-state intensity, SV gradually decreases and HR increases. Cardiac output is well maintained, but arterial blood pressure also declines. These alterations are called cardiovascular drift.
One theory: With more blood in the skin for the purpose of cooling the body, less blood is available to return to the heart, thus decreasing preload. There is also a small decrease in blood volume resulting from sweating and from a generalized shift of plasma across the capillary membrane into the surrounding tissues. These factors combine to decrease ventricular filling pressure, which decreases venous return to the heart and reduces the EDV.
Second Theory: As HR increases, there is less filling time for the ventricles. This exercise tachycardia may lower SV under the conditions of prolonged exercise even without peripheral displacement of blood volume.
Describe the primary functions of blood.
Blood is the fluid that carries oxygen and nutrients to the tissues and clears away waste products of metabolism. With exercise, more oxygen is required by the active muscles; therefore more oxygen is extracted from the blood.
How does pulmonary ventilation respond to increasing intensities of exercise?
Pulmonary ventilation increases during exercise in direct proportion to the metabolic needs of exercising muscle. At low exercising intensities, this is accomplished by increases in tidal volume (the amount of air moved in and out of the lungs during regular breathing). At higher intensities, the rate of respiration also increases.
What role does the respiratory system play in acid-base balance?
The three major chemical buffers in the body are bicarbonate, inorganic phosphates, and proteins. Hemoglobin in the red blood cells is also a major buffer. Whenever H+ concentration starts to increase, the inspiratory center responds by increasing the rate and depth of respiration. Removing carbon dioxide is an essential means of removing H+ concentrations. Bicarbonate ions can buffer the H+ to prevent acidosis.
Discuss the different theories that have attempted to explain how muscles gain strength with training.
An important component of the strength gains that result from resistance training are neural adaptations. Motor unit recruitment, frequency of motor nerve firing rates, better synchronization of motor units during a particular movement, and other neural factors are important to strength gains. Strength gains may result from changes in the connections between motor neurons located in the spinal cord, allowing motor units to act more synchronously. The increase in neural drive of alpha-motor neurons could also increase the frequency of discharge, or rate coding, of their motor units.
Differentiate between transient and chronic muscle hypertrophy.
Transient hypertrophy is the increased muscle size that develops during and immediately following a single exercise bout. This results mainly from fluid accumulation (edema) in the interstitial and intracellular spaces of the muscle that comes from the blood plasma. This only lasts for a short amount of time. Chronic hypertrophy refers to the increase in muscle size that occurs with long-term resistance training. This reflects actual structural changes in the muscle that can result from an increase in the size of existing individual fibers (fiber hypertrophy), in the number of muscle fibers (fiber hyperplasia), or both.
What is fiber hyperplasia? How might it occur? How might it be related to gains in size and muscle strength with resistance training?
Fiber hyperplasia is an increase in the total number of fibers within the muscle. It is possible that only very high intensity in resistance training can result in fiber hyperplasia, and even then, the percentage of the total muscle size increase due to this phenomenon is small, perhaps 5% to 10%.
To support protein synthesis during resistance training, what type of protein should be ingested and how much?
The best forms of protein for muscle hypertrophy are easily and rapidly digested and rich in essential amino acids, especially leucine. Whey protein found in milk is one source that meets both of these goals. Although ingestion of relatively small amounts of protein (5-10g) is capable of stimulating muscle protein synthesis, to make muscles larger, one should consume larger amounts of protein, 20-25g, immediate following resistance exercise.
Is there an optimal timing of protein ingestion when an individual is trying to optimize the hypertrophic response to successive exercise sessions?
The protein synthesis-stimulating effect of a single dose of amino acids is transient and lasts only 1-2 hours. Ingesting repeated small doses of protein during recovery from resistance training may be more effective in increasing muscle hypertrophy, as opposed to just eating one large meal.
What is maximal oxygen uptake (VO2(max))? How is it defined psychologically, and what determines its limits?
VO2(max) is the highest rate of oxygen consumption attainable during maximal or exhaustive exercise. As exercise intensity increases, oxygen consumption eventually either plateaus or decreases slightly even with further increases in workload, indicating that a true maximal VO2 has been achieved.
Describe the changes in the oxygen transport system that occur with endurance training.
The (a-v)O2 difference increases with training, particularly at maximal exercise intensity. This increase results from a lower mixed venous oxygen content, which means that the blood returning to the heart (which is a mixture of venous blood from all body parts, not just active tissues) contains less oxygen than it would in an untrained person. This reflects both greater oxygen extraction by active tissues and a more effective distribution of blood flow to active tissues. The increased extraction results in part from an increase in oxidative capacity of active muscle fibers.
What metabolic adaptations occur in response to endurance training?
Metabolic adaptations to training include lactate threshold, respiratory exchange ratio, and oxygen consumption. The higher the lactate threshold, the better the performance capacity. The respiratory exchange ratio (RER) is the ratio of carbon dioxide released to oxygen consumed during metabolism. After training, the RER decreases at both absolute and relative submaximal exercise intensities. These changes are attributable to a greater utilization of free fatty acids instead of carbohydrate at these work rates following training. VO2(max) is the best indicator of cardiorespiratory endurance capactiy and increases substantially in response to endurance training.
What adaptations have been shown to occur in muscle fibers with anaerobic training?
Both type IIa and type IIx muscle fibers undergo an increase in the cross-sectional areas. The cross-sectional area of type 1 fibers also is increased but usually to a lesser extent. With sprint training, there seems to be a reduction in the percentage of type I fibers and an increase in the percentage of type II fibers, with greatest change in type IIa fibers.
What are the four major avenues for loss of body heat?
Conduction: involves the transfer of heat from one solid material to another through direct molecular contact. Ex. heat can be lost from the body when the skin is in contact with a cold object, as when one sits on cold metal bleachers.
Convection: involves the transferring heat by the motion of a gas or a liquid across the heated surface. The greater the movement of the air (or liquid, such as water), the greater the rate of heat exchange by convection.
Radiation: the skin constantly radiates heat in all directions to objects around it, such as clothing, furniture, and walls, but it can also receive radiant heat from surrounding objects that are warmer.
Evaporation: is the primary avenue for heat dissipation during exercise. When air temperature is close to skin temperature, the only available means of cooling is evaporation.
What happens to the body temperature during exercise, and why?
Internal body temperature at rest is regulated at approximately 37 degrees Celcius. During exercise, the body is often unable to dissipate the heat as rapidly as it is produced. The muscle's energy systems become more chemically efficient with a small increase in muscle temperature. Sensory receptors called thermoreceptors detect changes in temperature and relay this information to the body's thermostat, located in a region of the brain called the preoptic-anterior hypothalamus (POAH).
What is the purpose of the wet-bulb globe temperature (WBGT)? What does it measure?
WBGT was devised to simultaneously account for conduction, convection, evaporation, and radiation. It is based on three different thermometer readings and provides a single temperature reading to estimate the cooling capacity of the surrounding environment. As water evaporates from the wet bulb, its temperature will be lower than dry bulb (the actual air temperature one would measure with a typical thermometer), reflecting the effect of sweat evaporating from the skin.
Differentiate between heat cramps, heat exhaustion, and heatstroke.
Heat cramps: the least serious of the three heat disorders, characterized by severe and painful cramping of large skeletal muscles. Brought on by sodium losses and dehydration that accompany high rates of sweating.
Heat exhaustion: accompanied by such symptoms as extreme fatigue, dizziness, nausea, vomiting, fainting, and a weak, rapid pulse. It is caused by the cardiovascular system's inability to adequately meet the needs of the body as it becomes severely dehydrated. The thermoregulatory mechanisms are functioning but cannot dissipate heat quickly enough because insufficient blood volume is available to allow adequate blood flow to the skin.
Heatstroke: a life-threatening heat disorder that requires immediate medical attention. Caused by failure of the body's thermoregulatory mechanisms. Characterized by an increase in internal body temperature to value exceeding 40 degrees C (104 degrees F) and confusion, disorientation, or unconsciousness. Cessation of active sweat may also occur.
How does the body minimize excessive heat loss during cold exposure?
The hypothalamus has a temperature "set point" of about 37 degrees C (98.6 degrees F). A decrease in either skin or blood temperature provides feedback to the thermoregulatory center (POAH) to activate mechanisms that conserve body heat and increase heat production. The primary means by which our bodies minimize excessive heat loss during cold exposure are are peripheral vasoconstriction (constricts the arterioles, reduces the blood flow to the shell of the body and minimizes heat loss), non-shivering thermogenesis (stimulation of metabolism by the SNS is increased to increase heat production), and shivering (a rapid, involuntary cycle of contraction and relaxation of skeletal muscles, which increases heat).
Describe the conditions at altitude that could limit the ability to perform physical activity.
Low altitude: performance may be diminished, especially in athletes performing above 1,500m, may be overcome with acclimation.
Moderate altitude: Effects on well-being in unacclimated individuals and decreased maximal aerobic capacity and performance are likely. Optimal performance may or may not be restored with acclimation.
High altitude: Adverse health effects (including acute mountain sickness) in a large percentage of individuals and significant performance decrements, even after full acclimation.
Extreme altitude: Severe hypoxic effects are experienced.
What types of exercise are detrimentally influenced by exposure to high altitude and why?
Prolonged endurance performance suffers the most at high altitude because oxidative energy production is limited. Anaerobic sprint activities that last 2 minutes or less are generally not impaired at moderate altitude.
When someone ascends to an altitude of over 1,500m, describe the physiological adjustments that occur within the first 24 hr.
Hypoxic conditions stimulate the renal release of EPO, which increases erythrocyte (red blood cell) production in bone marrow. More red blood cells means more hemoglobin. Although plasma volume decreases initially, which helps concentrate the hemoglobin, it eventually returns to normal. These changes increase the blood's oxygen-carrying capacity.
What are the best strategies for preparing athletes for high-altitude competition?
One option is to compete as soon as possible after arriving at altitude, within 24 hours of arrival. This does not provide the beneficial effects of acclimation, but the altitude exposure is brief enough that the classic symptoms of altitude sickness are not yet totally manifested. Another option is to train at higher altitudes for a minimum of 2 weeks before competing, but 2 weeks is not even sufficient for total acclimation. Total altitude acclimation would require a minimum of 3 to 6 weeks, and usually even longer.