L2. Exercise metabolism Flashcards
What is the main purpose of exercise metabolism?
To convert chemical energy into kinetic energy
What are the key requirements for exercise metabolism?
Fuel availability, gas exchange, and circulation
What is factorial aerobic scope?
The ratio of oxygen consumption at peak exercise to resting levels
What limits exercise capacity during maximal efforts?
Fatigue, substrate stores, metabolic byproducts, or equipment failure
What is the most energy-dense substrate in the body?
Fat, with 9.3 calories per gram
Why is glycogen a less efficient energy store compared to fat?
Glycogen is stored with water, making it heavier per calorie
What role do ketones play in exercise metabolism?
They act as a link between fat stores and brain energy needs
What limits oxygen diffusion in the lungs during exercise?
Thickened alveolar-capillary barriers, such as in pulmonary fibrosis
How does ventilation adapt to exercise?
Increases up to 17-fold to eliminate CO2
What are the immediate energy sources for muscle contraction?
Phosphocreatine and ATP
What energy system supports fast ATP production without oxygen?
Anaerobic glycolysis
What is the TCA cycle, and why is it essential?
It is the citric acid cycle responsible for oxidative metabolism of substrates
What experiment demonstrated muscle glycogen depletion?
Bergstrom and Hultman’s 1966 study with one-legged cycling and biopsies
What is the role of glycogen in fat oxidation?
Glycogen provides intermediates needed for the TCA cycle to oxidize fat
Why does hitting the wall occur in endurance events?
Depleted glycogen prevents the regeneration of TCA cycle intermediates
What is anaplerosis?
The replenishment of TCA cycle intermediates from other substrates
How do phosphocreatine stores replenish during exercise?
Through ATP generated via oxidative phosphorylation
What substrate contributes most to energy during submaximal exercise?
Free fatty acids
What determines the predominant energy substrate during exercise?
Exercise intensity and duration
What is the role of type I muscle fibers in exercise?
They support endurance activities using oxidative metabolism
Why are type IIx muscle fibers important for sprinting?
They support fast and forceful contractions using glycolysis
What is the significance of PEPCK in metabolism?
It facilitates the shuttling of carbons into TCA cycle intermediates
What experiment highlighted fat burning in the presence of carbohydrates?
Knox and colleagues’ 1948 rabbit kidney and fumarate study
Why do some athletes train in a low-carbohydrate state?
To upregulate fat oxidation pathways for endurance
What limits sprint performance physiologically?
Speed and force of contraction of fast-twitch muscle fibers
How do athletes optimize glycogen stores?
By carbohydrate loading after exhaustive exercise
What happens to lactate during low-intensity exercise?
It is oxidized by type I fibers or recycled by the liver into glucose
What role does the liver play in exercise metabolism?
Recycling lactate into glucose via the Cori cycle
What adaptation allows endurance athletes to burn more fat?
Increased mitochondrial density and fat oxidation capacity
How does exercise intensity affect fuel utilization?
Higher intensities increase reliance on glycogen and glucose
Why is fat a better energy store for mobility?
It is lightweight and energy-dense compared to glycogen
What experiment demonstrated the role of TCA intermediates in oxidation?
Cold-fasted rat liver extracts improved fatty acid oxidation
What is the primary limiting factor in submaximal endurance exercise?
Carbohydrate availability for anaplerosis
What are carbohydrate response elements?
Transcriptional regulators promoting fat oxidation under low-carb conditions
What did Romijn’s study reveal about exercise metabolism?
Fuel source transitions from fats to carbohydrates as exercise intensity rises
Why does glycogen depletion not mean running out of fuel?
Fat stores remain abundant but cannot sustain the TCA cycle alone
What limits oxidative capacity when glycogen is depleted?
Exhaustion of anaplerotic TCA intermediates
How does the heart contribute to fuel selection during exercise?
It preferentially oxidizes lactate and free fatty acids
Why are ketones less relevant in modern human metabolism?
Frequent feeding suppresses ketogenesis and reliance on ketones
What is the relationship between carbon dioxide production and ventilation during exercise?
Ventilation increases to eliminate carbon dioxide produced during metabolism
