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NASM Chapter 3RESPIRATORY SYSTEM and CHRONIC ADAPATATIONS TO EXERCISE OF THE CARDIORESPIRATORY SYSTEM Learning Objectives This lesson covers how the Respiratory System responds to the demands of exercise and the physiological adaptations that occur with specific training programs. Upon completion of this chapter, you will be able to: – Describe the anatomy and physiology of the respiratory system – Describe the acute and chronic responses to aerobic training Respiratory System: Introduction The functions of the respiratory system include: – Replacing oxygen and removing carbon dioxide from the blood – Vocalization – Regulation of the acid-base balance during exercise Components of the respiratory system include the nose, nasal cavity, pharynx, larynx, trachea, bronchi, and lungs. – They form a passage that filters air and transports it to the lungs. – Gas exchange occurs in the lungs in the alveoli. – Lungs contain an estimated 300 million alveoli providing a surface area about the size of a tennis court). Respiratory System: Pulmonary Ventilation Pulmonary ventilation is the process by which air is moved into and out of the lung (inspiration, expiration) Inspiration is an active process in which the diaphragm and intercostal muscles contract, increasing dimensions and volume of the thoracic cage Expiration at rest is normally passive; the inspiratory muscles relax, decreasing the thoracic cage Forced inspiration and expiration are active processes involving accessory muscles The air exchange rate increases from 5 to 6 liters of air per minute at rest to 20 to 30 liters per minute during exercise. Dysfunctional Breathing If there is a dysfunction in the cardiorespiratory system, this can directly impact the components of the HMS and perpetuate into further dysfunction. Alterations in breathing patterns are a prime example of this relationship: – During shallow breathing patterns, the secondary respiratory muscles are used more predominantly. – If this shallow, upper-chest breathing pattern becomes habitual, it can cause overuse of muscles, including the scalenes, sternocleidomastoid, levator scapulae, and upper trapezius. – These muscles also play a major postural role in the kinetic chain, as they all connect directly to the head and neck. – Their increased activity and excessive tension often result in headaches, lightheadedness, and dizziness. Physiology of the Cardiorespiratory System For muscles to contract, they need energy in the form of adenosine triphosphate (ATP). The cardiorespiratory system is responsible for the three basic processes to produce this energy: – Get oxygen into the blood (oxygen-carrying capacity) – Deliver oxygen to the muscles (oxygen delivery) – Extract the oxygen from the blood to form ATP (oxygen extraction) Oxygen-carrying capacity is affected by two primary factors: – The ability to adequately ventilate the alveoli in the lungs – The hemoglobin concentration in the blood Oxygen Extraction Oxygen extraction from the blood at the cellular level depends on muscle-fiber type and the availability of specialized oxidative enzymes. – Slow-twitch muscle fibers are specifically adapted for oxygen extraction and utilization. – Aerobic production of ATP occurs in the mitochondria of the cells. – The circulatory system increases blood flow to the active muscles and decreases blood flow to non-active areas such as the viscera, allowing a higher concentration of O2 to be extracted. – Oxygen extraction can be measured by a-v-O2 difference (i.e. the difference between oxygen in the arteries versus the veins). Oxygen Consumption The usage of oxygen by the body is known as oxygen consumption – At rest = 3.5ml∙kg·min – Approximately 5 kcal of energy are burned for every liter of oxygen consumed. VO2max, or maximal oxygen consumption is generally accepted as the best means of gauging cardiorespiratory fitness. – Submaximal testing procedures have been established to estimate maximal oxygen consumption. – The more oxygen a person can take in, deliver, and utilize, the more work he or she can perform. – It is expressed in either “relative” terms (mL/kg/min) or “absolute” terms (L/min). Oxygen Consumption during exercise As soon as aerobic exercise begins, the sympathetic nervous system stimulates an increase in cardiac output and the release of epinephrine and norepinephrine. Oxygen Deficit: It takes two to four minutes for the body to meet the increased metabolic demand of oxygen. – During this time, the anaerobic energy systems take over. Steady State: When the cardiorespiratory system has fully taken over, a new level of steady-state oxygen consumption is achieved. EPOC: Excess Post-exercise Oxygen Consumption: Oxygen consumption slowly declines, but remains elevated above resting level, a.k.a “afterburn” Anaerobic Threshold The anaerobic threshold (AT) is reached when exercise intensity increases above steady-state aerobic metabolism and anaerobic production of ATP occurs. Anaerobic threshold or lactate threshold is generally when a person becomes “out of breath” and cannot sustain that level of intensity for more than a few minutes. – Lactate accumulates progressively in the blood and the oxygen deficit and corresponding EPOC are extremely high. – At this point, the body attempts to rid excess CO2 (a by-product of acid metabolites) through increased ventilatory rate. Summary The respiratory system gathers oxygen from the environment, inhales it through the nose and mouth, and processes it to be delivered to the tissues of the body. As cells use oxygen, they produce carbon dioxide, which is transported back to the heart and lungs in the deoxygenated blood to be released through exhalation. The collection and transportation of oxygen is made possible by the respiratory pump and the respiratory airways. If there is a dysfunction in the cardiorespiratory system, this can directly impact the components of the HMS and perpetuate into further dysfunction. Acute Responses to Exercise Going from rest to exercise requires the circulatory and respiratory systems to increase oxygen delivery. To meet the increased demands of the muscles, two major adjustments in blood flow occur: – Redistribution of blood flow from the inactive organs to the active skeletal muscles – Increased cardiac output (Q = SV x HR) Regulation of heart rate is controlled: – Intrinsically by the sinoatrial node (SA node) – Extrinsically by the nervous and endocrine systems – Changes in heart rate are influenced by the parasympathetic and sympathetic divisions of the autonomic nervous system (ANS). Blood Pressure During Exercise Systolic blood pressure has a much higher increase during exercise than diastolic blood pressure due to: – Increased contractility of the heart – Increased stroke volume – The muscular need for greater force and pressure to deliver blood to the exercising muscles – Vasodilation within the exercising muscle, which results in more blood draining from the arteries, through the arterioles, and into muscle capillaries Ventilatory Regulation Aerobic exercise results in: – An increase of oxygen to the working tissues – Increased return of carbon dioxide to the lungs – An increase in the volume of air breathed per minute (minute ventilation—VE) During submaximal exercise, ventilation increases proportionately with increased oxygen consumption and carbon dioxide production. As intensity increases to near maximal, the minute ventilation increases disproportionately to oxygen consumption. Ventilatory Response to Exercise Ventilatory response to exercise increases linearly, with the exception of two distinct deflection points at the first and second ventilatory thresholds (VT1 and VT2). – VT1 represents the increased respiratory response to remove extra CO2 produced by the buffering of lactate as it begins to accumulate in the blood. – VT2 represents the blood buffering systems becoming overwhelmed by rapidly increasing blood lactate. Chronic Adaptations: Muscle-buffering Capacity Muscle-buffering capacity refers to the muscles’ ability to neutralize the lactic acid that accumulates in them during high-intensity activity. – Delays the onset of fatigue – Allows the exerciser to perform at a higher intensity and duration before “hitting the wall” Training at the lactate threshold will enhance buffering capacity and delay muscle fatigue for subsequent training sessions. Ventilatory threshold is an indirect representation of lactate threshold. – Endurance training improves the ability to sustain high levels of submaximal ventilation. Chronic Adaptations: CV Changes Regular, consistent exercise leads to several adaptations that allow the body to improve performance. Cardiorespiratory changes – Cardiorespiratory endurance capacity is determined by the ability of the cardiovascular and respiratory systems to deliver oxygen to active tissues, and the ability of those tissues to extract and use the oxygen during prolonged bouts of exercise. Chronic Adaptations: Blood Volume Increase in blood volume – An initial, rapid adaptation to exercise – Increase is due primarily to plasma and, to a lesser extent, red blood cells – Plasma volume can increase 12 to 20% after three to six aerobic-training workouts. – The number of red blood cells may increase, but the ratio of red blood cell volume to total blood volume may decrease. Chronic Adaptations: Heart Size and Volume Heart size and volume – Increase as an adaptation to increased work demand, but return to pre-training levels within several weeks if training ceases – Characterized by an increase of the left ventricular cavity and slight thickening of the walls – Increase in size is due to endurance training and an increase in blood volume – These adaptations lead to an increase in cardiac force and the amount of blood pumped per beat. – Decreased resting heart rate (RHR) and exercise heart rate for a given intensity allow for longer diastolic filling and a reduced work requirement for the heart. – Improved maximal oxygen uptake (VO2max) and decreased cardiac stress Chronic Adaptations: CV Components Improvements in VO2max are due to increases in one or more of the following variables: – Stroke volume • Increases at rest and during exercise result from regular training – Heart rate • Regular training typically yields: – Decreased RHR of more than 10 bpm – Decreased submaximal heart rate of 10–20 bpm – a-vO2 difference • Increases with training, particularly at maximal exercise • Reflective of greater oxygen extraction at the tissue level and more effective distribution of blood flood to active tissue Cardiorespiratory Changes: Blood Flow and Pressure Blood flow – Increased blood flow to working muscles is enhanced through regular endurance training due to: • Increased capillarization of trained muscles • Greater recruitment of existing capillaries in trained muscles • More effective blood flow redistribution from inactive areas to active tissues • Increased blood volume Blood pressure – In response to regular endurance training, a decrease in resting SBP and DBP is noted. – Resistance training may also reduce SBP. Cardiorespiratory Changes: Oxidative Enzymes Oxidative enzymes – Responses to regular endurance training include: • Increase in the size and number of mitochondria in skeletal muscle – Enhances the muscle’s ability to use oxygen and produce ATP via oxidation • Increase in the activity of the mitochondrial oxidative enzymes – Slower rate of muscle glycogen utilization – Enhanced reliance on fat as fuel at any given exercise intensity Summary Understanding the transition from rest to exercise and the adaptations that occur in response to regular training is essential for proper exercise selection and program design. This lecture covered: – Respiratory System, Cardiorespiratory interaction – Acute responses to exercise – Chronic adaptations to exercise