Adaptations to Aerobic Endurance Training Programs

Adaptations to Aerobic Endurance Training Programs chapter6 Adaptationsto Aerobic EnduranceTraining Programs Ann Swank, PhD, CSCS, FACSM

Chapter Objectives • Identify and describe acute responses of the cardiovascular and respiratory systems to aerobic exercise. • Identify and describe the impact of chronic aerobic endurance training on the physio-logical characteristics of the cardiovascular, respiratory, nervous, muscular, bone and connective tissue, and endocrine systems. (continued)

Chapter Objectives (continued) • Recognize the interaction between designing aerobic endurance training programs and optimizing physiological responses of all body systems. • Identify and describe external factors that influence adaptations to acute and chronic aerobic exercise. • Recognize the causes, signs, symptoms, and effects of overtraining and detraining.

Section Outline • Acute Responses to Aerobic Exercise • Cardiovascular Responses • Cardiac Output • Stroke Volume • Heart Rate • Oxygen Uptake • Blood Pressure • Control of Local Circulation • Respiratory Responses • Gas Responses • Blood Transport of Gases and Metabolic By-Products

Acute Responses to Aerobic Exercise • Cardiovascular Responses • Cardiac Output • From rest to steady-state aerobic exercise, cardiac output initially increases rapidly, then more gradually, and subsequently reaches a plateau. • With maximal exercise, cardiac output may increase to four times the resting level.

Key Terms . • cardiac output (or Q): The amount of blood pumped by the heart in liters per minute (SV × HR). • stroke volume: The quantity of blood ejected with each beat.

Acute Responses to Aerobic Exercise • Cardiovascular Responses • Stroke Volume • End-diastolic volume is significantly increased. • At onset of exercise, sympathetic stimulation increases stroke volume. • Heart Rate • Heart rate increases linearly with increases in intensity. • Oxygen Uptake • Oxygen uptake increases during an acute bout of aerobic exercise and is directly related to the mass of exercising muscle, metabolic efficiency, and exercise intensity.

Key Term • maximal oxygen uptake: The greatest amount of oxygen that can be used at the cellular level for the entire body.

Key Term • resting oxygen uptake: Estimated at 3.5 mlof oxygen per kilogram of body weight per minute (ml · kg–1 · min–1); this value is defined as 1 metabolic equivalent (MET).

Acute Responses to Aerobic Exercise • Cardiovascular Responses • Blood Pressure • Systolic blood pressure estimates the pressure exerted against the arterial walls as blood is forcefully ejected during ventricular contraction. • Diastolic blood pressure is used to estimate the pressure exerted against the arterial walls when no blood is being forcefully ejected through the vessels.

Blood Pressures in the Circulatory System • Figure 6.1 (next slide) • Blood pressures in the various portions of the circulatory system

Figure 6.1 Reprinted, by permission, from Guyton, 1991.

Acute Responses to Aerobic Exercise • Cardiovascular Responses • Control of Local Circulation • During aerobic exercise, blood flow to active muscles is considerably increased by the dilation of local arterioles. • At the same time, blood flow to other organ systems is reduced by constriction of the arterioles.

Key Point • Acute aerobic exercise results in increased cardiac output, stroke volume, heart rate, oxygen uptake, systolic blood pressure, and blood flow to active muscles and a decrease in diastolic blood pressure.

Acute Responses to Aerobic Exercise • Respiratory Responses • Aerobic exercise, as compared to other types of exercise, provides for the greatest impact on both oxygen uptake and carbon dioxide production.

Tidal Volume • Figure 6.2 (next slide) • The slide shows the distribution of tidal volume in a healthy athlete at rest. • The tidal volume comprises about 350 ml of roomair that mixes with alveolar air, about 150 ml of airin the larger passages (anatomical dead space),and a small portion of air distributed to either poorly ventilated or incompletely filled alveoli (physiological dead space).

Figure 6.2 Reprinted, by permission, from McArdle, Katch, and Katch, 1996.

Key Point • During aerobic exercise, large amounts of oxygen diffuse from the capillaries into the tissues, increased levels of carbon dioxide move from the blood into the alveoli, and minute ventilation increases to maintain appropriate alveolar concentrations of these gases.

Acute Responses to Aerobic Exercise • Respiratory Responses • Gas Responses • During high-intensity aerobic exercise, the pressure gradients of oxygen and carbon dioxide cause the movement of gases across cell membranes. • The diffusing capacities of oxygen and carbon dioxide increase dramatically with exercise, which facilitates their exchange.

Pressure Gradients • Figure 6.3 (next slide) • The slide shows pressure gradients for gas transfer in the body at rest. • The pressures of oxygen (PO2) and carbon dioxide (PCO2) in ambient air, tracheal air, and alveolar air are shown. • The gas pressures in venous and arterial blood and muscle tissue are shown.

Figure 6.3 Reprinted, by permission, from Fox, Bowers, and Foss, 1993.

Acute Responses to Aerobic Exercise • Respiratory Responses • Blood Transport of Gases and Metabolic By-Products • Most oxygen in blood is carried by hemoglobin. • Most carbon dioxide removal is from its combination with water and delivery to the lungs in the form of bicarbonate. • During low- to moderate-intensity exercise, enough oxygen is available that lactic acid does not accumulate because the removal rate is greater than or equal to the production rate. • The aerobic exercise level at which lactic acid (converted to blood lactate at this point) begins to show an increase is termed the onset of blood lactate accumulation, or OBLA.

Section Outline • Chronic Adaptations to Aerobic Exercise • Cardiovascular Adaptations • Respiratory Adaptations • Neural Adaptations • Muscular Adaptations • Bone and Connective Tissue Adaptations • Endocrine Adaptations

Table 6.1 (continued)

Table 6.1 (continued) (continued)

Chronic Adaptations to Aerobic Exercise • Cardiovascular Adaptations • Aerobic endurance training requires proper progression, variation, specificity, and overload if physiological adaptations are to take place.

Chronic Adaptations to Aerobic Exercise • Respiratory Adaptations • Ventilatory adaptations are highly specific to activities that involve the type of exercise used in training. • Training adaptations include increased tidal volume and breathing frequency with maximal exercise. • Neural Adaptations • Efficiency is increased and fatigue of the contractile mechanisms is delayed.

Chronic Adaptations to Aerobic Exercise • Muscular Adaptations • One of the fundamental adaptive responses to aerobic endurance training is an increase in the aerobic capacity of the trained musculature. • This adaptation allows the athlete to perform a given absolute intensity of exercise with greater ease after aerobic endurance training.

Chronic Adaptations to Aerobic Exercise • Bone and Connective Tissue Adaptations • In mature adults, the extent to which tendons, ligaments, and cartilage grow and become stronger is proportional to the intensity of the exercise stimulus, especially from weight-bearing activities.

Chronic Adaptations to Aerobic Exercise • Endocrine Adaptations • Aerobic exercise leads to increases in hormonal circulation and changes at the receptor level. • High-intensity aerobic endurance training augments the absolute secretion rates of many hormones in response to maximal exercise. • Trained athletes have blunted responses to submaximal exercise.

Section Outline • Designing Aerobic Endurance Programs for Optimizing Adaptations

Key Points • One of the most commonly measured adaptations to aerobic endurance trainingis an increase in maximal oxygen uptake associated with an increase in maximal cardiac output. • The intensity of training is one of the most important factors in improving and main-taining aerobic power.

Key Point • Aerobic endurance training results in re-duced body fat, increased maximal oxygen uptake, increased respiratory capacity, lower blood lactate concentrations, increased mitochondrial and capillary densities, and improved enzyme activity.

Physiological Variables in Aerobic Endurance Training • Table 6.2 (next slides) • These subjects completed a short-term (three- to six-month) aerobic endurance training program. • BTPS = body temperature and pressure, saturated

Table 6.2 (continued)

Table 6.2 (continued) (continued) (continued)

Section Outline • External Influences on the Cardiorespiratory Response • Altitude • Hyperoxic Breathing • Smoking • Blood Doping

External Influences on the Cardiorespiratory Response • Altitude • Changes begin to occur at elevations greater than 3,900 feet (1,200 m): • Increased pulmonary ventilation • Increased cardiac output at rest and during submaximal exercise due to increases in heart rate • Values begin to return toward normal within two weeks. • Several chronic physiological and metabolic adjustments occur during prolonged altitude exposure.

Table 6.3

External Influences on the Cardiorespiratory Response • Hyperoxic Breathing • Breathing oxygen-enriched gas mixtures during rest periods or following exercise may positively affect exercise performance, although the procedure remains controversial. • Smoking • Acute effects of tobacco smoking could impair exercise performance. • Blood Doping • Artificially increasing red blood cell mass is unethical and poses serious health risks, yet it can improve aerobic exercise performance and may enhance tolerance to certain environmental conditions.

Section Outline • Individual Factors Influencing Adaptations to Aerobic Endurance Training • Genetic Potential • Age and Sex • Overtraining • Cardiovascular Responses • Biochemical Responses • Endocrine Responses • Detraining

Individual Factors Influencing Adaptations to Aerobic Endurance Training • Genetic Potential • The upper limit of an individual’s genetic potential dictates the absolute magnitude of the training adaptation. • Age and Sex • Maximal aerobic power decreases with age in adults. • Aerobic power values of women range from 73% to 85% of the values of men. • The general physiological response to training is similar in men and women.

Individual Factors Influencing Adaptations to Aerobic Endurance Training • Overtraining • Cardiovascular Responses • Greater volumes of training affect heart rate. • Biochemical Responses • High training volume results in increased levels of creatine kinase, indicating muscle damage. • Muscle glycogen decreases with prolonged periods of overtraining. • Endocrine Responses • Overtraining may result in a decreased testosterone-to-cortisol ratio, decreased secretion of GH, and changes in catecholamine levels.

Key Point • Overtraining can lead to dramatic performance decreases in athletes of all training levels and is caused by mistakesin the design of the training program.

Individual Factors Influencing Adaptations to Aerobic Endurance Training • What Are the Markers of Aerobic Overtraining? • Decreased performance • Decreased percentage of body fat • Decreased maximal oxygen uptake • Altered blood pressure • Increased muscle soreness • Decreased muscle glycogen • Altered resting heart rate (continued)

Individual Factors Influencing Adaptations to Aerobic Endurance Training • What Are the Markers of Aerobic Overtraining? (continued) • Increased submaximal exercise heart rate • Decreased lactate • Increased creatine kinase • Altered cortisol concentration • Decreased total testosterone concentration • Decreased ratio of total testosterone to cortisol (continued)

Individual Factors Influencing Adaptations to Aerobic Endurance Training • What Are the Markers of Aerobic Overtraining? (continued) • Decreased ratio of free testosterone to cortisol • Decreased ratio of total testosterone to sex hormone–binding globulin • Decreased sympathetic tone (decreased nocturnal and resting catecholamines) • Increased sympathetic stress response

Individual Factors Influencing Adaptations to Aerobic Endurance Training • Detraining • If inactivity, rather than proper recovery, follows exercise, an athlete loses training adaptations.

Adaptations to Aerobic Endurance Training Programs