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Chapter 6 - Physiological Responses and Adaptations to Aerobic Endurance Training

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    Chapter Objectives:

    • Find acute physiological responses to aerobic exercise.
    • Find chronic physiological adaptations to aerobic endurance training
    • Know the factors influencing adaptations to aerobic endurance training.
    • Know and find the physiological factors that go with overtraining.
    • Know the physiological consequences of detraining.

    Acute Responses to Aerobic Endurance Exercise

    Cardiovascular Responses

    Two components are affected: the heart and the vasculature

    While exercising, we have an increase stimulation or excitation of the heart occurring so that we are able to supply blood to the skeletal muscles that are working. 

    Stroke volume increases to maximal levels at 40 – 60% VO2 max and plateau long before becoming exhausted.

    The Frank-Starling Mechanism says that the stroke volume of the heart increases proportionally to the volume of the blood that is filling the heart.

    As we increase from resting states to max exercise intensity, we have a 50 – 60% reduction in the total peripheral resistance. This reduction happens from vasodilation from efforts to supply the working skeletal muscles what they need.

    Blood to the other parts of the body is decreased while doing this exercise.

    Blood pressure is the force exerted on blood vessels. Systolic blood pressure is the force when contracting, Diastolic blood pressure is the force when resting.

    Mean arterial blood pressure raises during exercise and is expressed in numbers by the formula MAP = DBP + (0.333 X (SBP – DBP))

    Rate pressure product shows how. Much oxygen the heart is needing. The formula is RPP = HR X SBP

    Cardiac output, heart rate, stroke volume, mean arterial pressure, coronary artery diameter, and rate pressure product raise during exercise.

    Respiratory Responses

    Pulmonary minute ventilation is breathing rate times tidal volume. This is the amount of air that is moved in or out of the lungs in a minute. This increases during exercise due to the need for oxygen that increases.

    The respiratory quotient is volume of Co2 production divided by oxygen consumption at the cellular level. This is also termed as the respiratory exchange ratio (RER).

    The RQ is about 0.82 at rest. Both the ratios RQ/RER approach 1.0 as we increase intensity and energy from carbs increases.

    During the most intense exercise, the RER and RQ can be higher than 1.0 due to hyperventilation. This increases the amount of CO2 expired from the body compared to oxygen taken in.

    The RER can be also used as an exercise intensity reading.

    Metabolic Responses

    Aerobic exercise is very inefficient in someone who is untrained and beginning a program. 

    The body consumes more oxygen when exercising and then needs more ATP. 

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    The difference in oxygen in the arterial and mixed venous blood is known as the arteriovenous oxygen difference. This represents the extent at which the oxygen is removed from the blood as it goes through the body.

    The oxygen consumed volume is known as the product of Q and the arteriovenous oxygen difference. This is known as the Fick Equation.

    More CO2 and Lactate is produced due to metabolism increasing, and thus we see higher concentration in the body. All of these cause an increase in blood acidity.

    Endocrine Responses

    The main purpose of the endocrine system in one bout of exercise is to allow metabolism by maintaining the availability of carbs and fats needed to meet increased energy demands.

    The pancreas is the endocrine gland playing the biggest role in acute exercise metabolism due to the release and production of glucagon and insulin. These hormones are responsible for he release and uptake of glucose in the body, which is very vital to survival and explains the increased metabolism.

    Cortisol is the only hormone from the adrenal cortex that plays any role in metabolism. This hormone is responsible for the stimulation of proteins used in the aerobic systems and glycolysis. It also plays a role in maintaining the level of blood sugar and promoting the use of fats for energy. Exercise intensity highly effects the secretion of cortisol. The higher the intensity, the more that is secreted.

    Catecholamines, epinephrine and norepinephrine, are the fight or flight hormones released form the adrenal medulla when given instruction from the sympathetic nervous system in stressful times. 

    Chronic Adaptation to Aerobic Exercise

    This will discuss effects on the skeletal muscle, bone, connective tissue, metabolism, body composition, and performance. 

    Cardiovascular Adaptations

    Maximal aerobic power is one of the key components for improving our aerobic exercise performance. This is known as a few different words: VO2 max, maximal oxygen uptake, maximal oxygen consumption, and aerobic capacity. These are used interchangeably.

     The Fick equation expresses oxygen uptake and it indicates the body’s ability to deliver oxygen. 

    Aerobic endurance training doesn’t affect max heart rate or potentially even decreases it slightly. 

    The higher the cardiac output, the higher the aerobic power.

    When resting or at any of the fixed Submax intensities, the adaptations are decreases in heart rate and increases in stroke volume. 

    Training reductions in heart rate occur at about 2 weeks, but depending on other factors, they may take up to 10 weeks.

    Aerobic exercise in the long term will lead to moderate cardiac hypertrophy shown by left ventricular cavity enlargement and increases in the thickness of the left ventricular volume, ventricular filling time from training-induced brachy cardia, and improved cardiac contractile function.

    People with hypertension have significant reductions in their blood pressure resulting from long term aerobic exercise.

    Trained peripheral skeletal muscle increases in capillary density per unit of muscle from prolonged aerobic training.

    Respiratory Adaptations

    There are fewer cardiovascular system and skeletal muscle changes occurring from chronic aerobic training. 

    For most, the respiratory system does not limit the performance of max exercise. 

    The pulmonary minute ventilation may decrease by as much as 20 – 30% in Submax work, and 15 – 25% in in max exercise. It may not change at all at rest.

    With long term aerobic training, Submax changes include increases in tidal volume, and decreases in frequency of breathing. But both these factors increase when maximally exercising.

    Skeletal Muscle Adaptations

    Chronic aerobic training will not affect muscle size at the microscopic level, and really has no effect. The only real effect may occur in the small type I fibers and be no change or a slight increase in the cross-sectional area of the fibers.

    Enhanced performance during aerobic activities serves as the main change in skeletal muscle. These changes rely on changes in efficiency that are caused from regular training.

    We have the intramuscular stores of glycogen increasing with chronic training. This leads to less fatigue in the muscles over long activities. 

    Metabolic Adaptations

    The main metabolic adaptations are increases in the reliance on fat as an energy source along with the reduction in the use of carbs while sub maximally exercising, increasing the lactate threshold, and increasing the max oxygen consumption.

    We are essentially able to perform at higher levels for longer periods of time.

    We have enhancements occurring in the blood supply, increases in the mitochondrial content, and the aerobic enzymes in those who are trained will enhance the ATP production greatly. 

    Endocrine Adaptations

    Aerobic endurance training typically will lead to a blunted response in hormone release at the same absolute level of Submax exercise. 

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    Favorable changes that occur from training will slow over the next 72 hours. But with chronic exercise we see that long term glucose control is not a consequence of chronic adaptation in muscle tissue functions.

    Bone and Connective Tissue

    There are moderate to high bone loading forces that will play a major role in maximizing our bone mass in childhood and early adulthood, along with maintaining your bone mass at middle age, and also attenuating bone mineral loss that occurs in older age. 

    Specificity and progression are important concepts to take into account when looking at exercising long term and bone mineral density. By exposing our body to the loads, we plan to take on in sports and activities, we allow the body to prepare the bones for that.

    The more intense the running is, the bigger the response and change in bone and connective tissue that will occur. An activity like walking will likely not increase the bone an connective tissue positively, but an activity like jogging will both help form stronger bone and connective tissue, and also maintain the health of these tissues.

    It is recommended that we maintain our bone and connective tissue health by combining both weight-bearing aerobic exercise and activities that involve jumping and resistance-based exercise. 

    Body Composition Adaptations

    Over 66% of adults in the US are either overweight or obese. 

    Aerobic endurance exercise has been known to enhance the sensitivity to insulin, reduce body fat, and favorably effect bone mineral density. All of these play vital roles in healthy body composition.

    Performance Adaptations

    Aerobic endurance training does not play a role in affecting other types of exercise like muscular strength, vertical jump performance, anaerobic power, or sprint speeds. It is mostly used to perform better with endurance activities.

    Factors That Influence Adaptations to Aerobic Endurance Training

    Specificity

    Adaptations occur as consequences of training and in a way that is specific to how you are training. For example, if you are training and doing some form of cycling, then, of course, your best benefits will be toward cycling and cycling related activities. 

    The body adapts to stress in as specific a way as possible. This should play a major role when designing a program for an individual.

    Genetics

    Everyone is born with a theoretical ceiling for human performance. This may or may not be attained. This value is dependent on many different variables like stimulus and motivation.

    One saying states that the best training for something involves choosing the right parents for it. That’s how big of a deal genetics are in athletics.

    Sex

    Physiological change are similar for both males and females.

    Women typically have less muscle mass and more body fat than men. This also means smaller lungs and heart and thus smaller blood volume. So, they will typically have a lower cardiac output, stroke volume, and VO2 max. They can increase comparatively to men, but since the starting values are lower, their max is lower, that’s the only typical difference.

    Age

    Max aerobic power increases as children grow older. Females reach their highest at 12 – 15, and males reach their highest at 17 – 21. We then plateau and then gradually decrease while we age.

    Overtraining

    This is present in aerobic training when intensity, duration, frequency, or any combination of the three are exceeded by an individual in their training over a lot of time. Exceeding adaption capacity while not recovering sufficiently will lead to decrements in performance-based upon the recovery times.

    Overreaching occurs in short term training and is when you don’t have sufficient recovery in your program. It could take days to weeks to fully recover from overreaching. 

    The common marker for overreaching and overtraining in aerobic endurance training are:

    • Decreases in performance
    • Decreases in VO2 max
    • Earlier onset of fatigue
    • General malaise
    • Loss of interest or enthusiasm in training
    • Psychological mood states being disturbed (maybe depression, anxiety or less vigor)
    • Increases in muscle soreness
    • Decreases in resting and max heart rate
    • Increases in Submax exercise heart rate
    • Decreases in Submax exercise plasma lactate concentration
    • Increases in sympathetic stress response
    • Decreases in catecholamine levels

    Detraining

    Responses to detraining are comparative to the responses to starting training.

    Muscular endurance decreases in just two weeks of ceasing activity. Other larger decreases in muscle respiratory ability, glycogen levels, and increase in lactate production will show up after about four weeks.

    If you want assistance wrapping your head around this material, make sure to check out Trainer Academy for some awesome NSCA study materials. They have Practice tests, flashcards, and a fantastic study guide. They even offer an exam pass guarantee.

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