Exercise Physiology and Responses

Exercise Physiology

• Physiological responses during incremental exercise intensity are covered.
• Maximum oxygen uptake (VO2 max) denotes the point where an individual can't increase oxygen consumption further.

Metabolic Response

• Oxygen uptake (VO2) increases with exercise intensity until it reaches a maximum or plateau.
• The respiratory system provides more oxygen, the cardiac system distributes more blood to active muscles, and the muscle metabolic systems use the increased oxygen.

Oxygen Consumption Relative to Exercise Intensity

• A graph shows oxygen consumption increasing with exercise intensity until it plateaus at VO2 max.

Respiratory Response

• Extra oxygen is delivered to the blood during exercise.
• Ventilation increases proportionally with oxygen uptake (VO2).
• Initially, ventilation increases due to both increased tidal volume and respiratory rate.
• But as exercise continues, tidal volume plateaus, and further increase in ventilation is solely due to a higher respiratory rate.

Three-Fold Increase in Oxygen Diffusing Capacity

• Pulmonary capillary perfusion increases, providing a greater surface area for oxygen diffusion.

Arterial-Venous Oxygen Content Difference (A-V O2)

• The difference between arterial and venous blood oxygen content.
• Exercise widens this difference for greater oxygen delivery.
• Increased blood flow to working muscles leads to higher oxygen extraction.

Cardiac Response

• Cardiac output (CO) increases in response to exercise to supply more blood to working muscles.
• Heart rate increases linearly with oxygen uptake, while stroke volume increases initially and reaches a plateau.
• The increase in CO is primarily based on heart rate after stroke volume reaches its peak.
• Maximum heart rate (MHR) is approximately 220 minus age.

Endocrine Response during Exercise

• Exercise raises blood levels of growth hormone, thyroxine, and aldosterone.

Physiological Adaptations to Regular Physical Training (Regulatory)

• Rapid responses within a few weeks of training.
• Shift from sympathetic to parasympathetic activity.
• Redistribution of blood flow.
• Initiation of sweating at a lower core temperature.
• Increased sensitivity to insulin to improve glucose tolerance at lower insulin levels.

Physiological Adaptations to Regular Physical Training (Structural)

• Slow changes over months or years.
• Increased muscle mass, cardiac tissue, and bone with increased capillary blood supply.
• Increased maximum oxygen consumption from increased enzyme activity in glycolysis.
• Increased aerobic capacity with higher myoglobin, Krebs cycle & mitochondrial function, with fat utilization sparing glycogen for anaerobic activity.
• Muscle fiber changes (mainly hypertrophy with more myofibrils, mitochondria, and stored ATP, glycogen, and triglycerides).

Respiratory Adaptations (Structural)

• Slower and deeper breathing pattern.

Cardiac Adaptations (Structural)

• Increase in the heart size (athlete's heart).
• High ventricular preload over time is the trigger for cardiac hypertrophy.
• Increased coronary artery cross-section along with higher capillary density and myocardial perfusion.

Possible Limitations to Maximal Oxygen Consumption

• Cardiovascular system components include central circulation (heart rate, stroke volume, hemoglobin concentration), peripheral circulation (flow to non-exercising areas, muscle capillary density, oxygen diffusion, and extraction), and hemoglobin-oxygen exchange).
• Respiratory factors include oxygen diffusion, ventilation, alveolar ventilation-perfusion ratio, and arteriovenous oxygen difference.
• Skeletal muscle factors include enzymes and oxidative potential, energy stores and delivery, myoglobin, and mitochondria number and size.

Physiological Adaptations to Regular Physical Training (Continued)

• Increased cardiac output during exercise depends more on stroke volume increase than heart rate increase during training.
• Athletes have a larger stroke volume at a lower heart rate, resulting in a 40-50% greater heart-pumping capacity.
• Autonomic activity modification reduces catecholamine output and its sensitivity, leading to a lower heart rate.

Effect of Drugs on Exercise Performance

• Caffeine in small quantities can improve exercise performance.
• Male sex hormones (androgens) can increase muscle strength but cause liver damage and affect reproductive health.
• Cocaine use in exercise performance can be deadly.

Key Points

• Alterations in metabolism, heart, and respiration occur during exercise.
• Physiological adaptations to exercise are regulatory and structural.