14.1 Exercise physiology and athletic performance

Exercise physiology explores how our bodies respond to physical activity. It looks at acute changes during a workout and long-term adaptations from regular training. This topic connects to the broader chapter by showing how our bodies adapt to different stressors.

Understanding exercise physiology helps us optimize athletic performance. We'll learn how the cardiovascular, respiratory, and muscular systems work together during exercise. We'll also explore energy production and how different types of training affect our bodies.

Physiological Changes During Exercise

Acute and Chronic Exercise

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• Acute exercise involves a single bout of physical activity while chronic exercise involves regular, repeated bouts of physical activity over an extended period of time
• During acute exercise, the cardiovascular system increases heart rate, stroke volume, and cardiac output to meet the increased demand for oxygen and nutrients in the working muscles
• Acute exercise leads to an increase in respiratory rate and depth of breathing to facilitate greater oxygen uptake and carbon dioxide removal
• Blood flow is redistributed during acute exercise, with increased flow to the working muscles and decreased flow to non-essential organs (digestive system)

Long-term Adaptations to Exercise

• Chronic exercise leads to long-term adaptations in the cardiovascular, respiratory, and muscular systems, resulting in improved efficiency and performance
• Regular exercise training increases the size and strength of the heart, allowing it to pump more blood with each contraction (increased stroke volume) and reducing resting heart rate
• Chronic exercise enhances the oxygen-carrying capacity of the blood by increasing the production of red blood cells and hemoglobin
• These adaptations improve the body's ability to deliver oxygen and nutrients to the working muscles during exercise, leading to better endurance and performance

Cardiovascular and Respiratory Systems in Athletic Performance

Cardiovascular System's Role

• The cardiovascular system, consisting of the heart and blood vessels, delivers oxygen and nutrients to the working muscles during exercise
• The heart's ability to pump blood efficiently (cardiac output) directly influences the amount of oxygen and nutrients that can be delivered to the muscles, making it a key determinant of athletic performance
• Cardiac output is the product of heart rate and stroke volume, both of which increase during exercise to meet the increased metabolic demands of the working muscles

Respiratory System's Role

• The respiratory system, which includes the lungs and airways, brings oxygen into the body and removes carbon dioxide
• During exercise, the respiratory system increases its rate and depth of breathing to meet the increased demand for oxygen and to remove the excess carbon dioxide produced by the working muscles
• The efficiency of the respiratory system in exchanging gases (oxygen and carbon dioxide) between the lungs and the blood is essential for maintaining optimal athletic performance
• Factors such as lung capacity, respiratory muscle strength, and the diffusion capacity of the lungs can influence an individual's respiratory efficiency during exercise

Interaction and Homeostasis

• The cardiovascular and respiratory systems work together to maintain homeostasis during exercise by regulating blood flow, blood pressure, and body temperature
• The cardiovascular system redistributes blood flow to the working muscles and skin (for heat dissipation) while reducing flow to non-essential organs
• The respiratory system helps to regulate blood pH by removing excess carbon dioxide, a byproduct of cellular metabolism that can lead to acidosis if not properly eliminated

Muscle Adaptations to Exercise Training

Resistance Training Adaptations

• Resistance training, which involves lifting weights or working against resistance, leads to an increase in muscle size (hypertrophy) and strength
• Hypertrophy occurs through an increase in the size of individual muscle fibers and an increase in the number of contractile proteins (actin and myosin) within each fiber
• Resistance training also leads to neural adaptations, such as improved motor unit recruitment and synchronization, which contribute to increased muscle strength

Endurance Training Adaptations

• Endurance training, such as long-distance running or cycling, leads to an increase in the number of mitochondria within the muscle cells, enhancing their capacity for aerobic energy production
• Endurance training increases the density of capillaries surrounding the muscle fibers, improving blood flow and oxygen delivery to the muscles
• Exercise training can lead to changes in muscle fiber type composition, with an increase in the proportion of slow-twitch (Type I) fibers in response to endurance training, which are more resistant to fatigue and have a higher oxidative capacity

Specificity and Reversibility

• The adaptations in skeletal muscle structure and function in response to exercise training are specific to the type of exercise performed
• For example, resistance training primarily leads to hypertrophy and strength gains, while endurance training primarily enhances oxidative capacity and fatigue resistance
• These adaptations are reversible if training is discontinued, emphasizing the importance of maintaining a consistent exercise program for long-term benefits

Energy Production During Exercise

Metabolic Pathways

• Energy production in the body involves the breakdown of nutrients (carbohydrates, fats, and proteins) to generate adenosine triphosphate (ATP), the primary energy currency of the cell
• The three main metabolic pathways for ATP production are the phosphagen system, glycolysis, and oxidative phosphorylation
• The phosphagen system, which involves the breakdown of creatine phosphate, provides rapid energy for short-duration, high-intensity activities (sprinting, weightlifting)
• Glycolysis is the anaerobic breakdown of glucose to produce ATP and lactate, and it is the primary energy source for moderate-intensity activities lasting up to several minutes

Oxidative Phosphorylation

• Oxidative phosphorylation, which occurs in the mitochondria, is the aerobic pathway that generates the most ATP and is the primary energy source for low-intensity, long-duration activities (marathon running)
• This pathway involves the complete oxidation of carbohydrates, fats, and proteins in the presence of oxygen, yielding large amounts of ATP
• The efficiency of oxidative phosphorylation depends on the availability of oxygen, the number and function of mitochondria in the muscle cells, and the activity of aerobic enzymes

Intensity, Duration, and Fuel Source

• The relative contribution of each metabolic pathway to energy production depends on the intensity and duration of the exercise, as well as the individual's fitness level and nutritional status
• High-intensity exercise relies more on the phosphagen system and glycolysis, while low-intensity exercise primarily uses oxidative phosphorylation
• As exercise duration increases, there is a gradual shift from carbohydrate metabolism to fat metabolism as the primary source of energy
• Well-trained individuals have a greater capacity to utilize fat as an energy source during exercise, which can help to spare glycogen stores and delay fatigue