24 Questions
What is the primary role of insulin during muscle glucose uptake?
Increasing glucose uptake through GLUT4
During a marathon, which fuel source is depleted in a few minutes?
Muscle glycogen
What is the primary function of glucagon during exercise?
Stimulating glycogenolysis in liver
What is the primary effect of adrenaline on muscle metabolism during exercise?
Stimulating glycogenolysis in muscle
What is the primary effect of growth hormone on fuel metabolism during a marathon?
Mobilizing fatty acids
What is the primary effect of cortisol on fuel metabolism during prolonged exercise?
Stimulating gluconeogenesis
What is the primary benefit of regular exercise on glucose metabolism?
Improved glucose tolerance
What is the primary characteristic of a marathon in terms of exercise intensity?
Low intensity, long duration
During high-intensity exercise, what is the primary mechanism for ATP regeneration?
Anaerobic pathways
Which of the following is NOT a function of the body's response to exercise?
Storing excess energy for future use
What is the primary fuel source for the brain during exercise?
Blood glucose
During a marathon, what is the approximate energy requirement per minute?
800 kJ/min-1
What is the primary function of glycogen storage in muscle cells?
To provide energy for high-intensity exercise
During low-intensity exercise, what is the primary source of energy for the muscles?
Fatty acids
What is the byproduct of anaerobic metabolism during high-intensity exercise?
Lactate
During exercise, what is the primary function of the liver's glycogen storage?
To support circulating glucose levels
What is the approximate duration of energy supply from stored glycogen in muscle cells during high-intensity exercise?
60 minutes
During high-intensity exercise, why is the body unable to deliver extra oxygen to the muscles?
Inability to increase oxygen delivery in time
What proportion of metabolism is anaerobic during the initial 30 seconds of exercise?
95%
What is the primary reason for the limited capacity of fatty acids as a fuel source during exercise?
All of the above
What is the primary source of energy during the finishing sprint phase of exercise?
Anaerobic metabolism of glucose from glycogen
What is the primary advantage of muscle glycogen as a fuel source during exercise?
It can be mobilized rapidly
What is the primary characteristic of exercise with a duration of 20 minutes or more?
95% aerobic metabolism
What is the primary destination of lactate released into the circulation during high-intensity exercise?
Liver for gluconeogenesis via the Cori cycle
Study Notes
Physiological Adaptations to Exercise
- Humans are well adapted to exercise, with many physiological and biochemical processes specifically configured to meet the acute oxygen and metabolic fuel needs of muscles.
- Exercise involves changes in multiple systems, including the musculo-skeletal, cardiovascular, respiratory, temperature, and urinary systems.
Metabolic Response to Exercise
- The body needs to mobilize stored fuels at a rate to match increased activity, preserving blood glucose levels to protect the brain.
- The magnitude and nature of the response depend on the type of exercise, intensity, duration, and physical condition and nutritional state of the individual.
Energy Requirements of Exercise
- Resting metabolic rate is approximately 4 kJ/min-1.
- Energy requirements increase with exercise intensity and duration, with examples including:
- 100m sprint: 200 kJ/min-1, 30 kJ total
- 1500m race: 140 kJ/min-1, 500 kJ total
- Marathon 42km: 800 kJ/min-1, 10,000 kJ total
Energy Sources
- ATP is required for muscle contraction, with very short-term stores lasting about 5 seconds.
- ATP must be rapidly recreated by oxidative phosphorylation (aerobic) and anaerobic pathways.
- Energy sources include:
- ATP and creatine phosphate (short-term stores)
- Glucose (circulation and tissue stores)
- Fatty acids (circulation and tissue stores)
- Glycogen (muscle and liver stores)
- Triacylglycerols (tissue stores)
Fuel Utilization
- During high-intensity exercise, ATP is created anaerobically, producing lactate and H+.
- During low-intensity exercise, aerobic metabolism uses fatty acids and glucose.
- The proportion of anaerobic to aerobic metabolism varies with exercise duration, with:
- 0-30 sec: 95% anaerobic
- 2-4 mins: 40-50% anaerobic
- > 20 min: 95% aerobic
Phases of Response
- Initial sprint: muscle ATP and creatine phosphate
- Long middle phase: aerobic metabolism of glucose from glycogen and fatty acids
- Finishing sprint: anaerobic metabolism of glucose from glycogen
Mobilizing Reserves
- Insulin and glucagon play key roles in mobilizing glucose and glycogen stores.
- Adrenaline and growth hormone stimulate glycogenolysis and lipolysis.
- Cortisol mobilizes fats and stimulates gluconeogenesis.
Benefits of Exercise
- Regular exercise produces improved exercise capacity, adaptations, and multiple health benefits, including:
- Better balance of lean tissue and fat
- Lower blood lipids and blood pressure
- Improved glucose tolerance and insulin sensitivity
- Reduced risk of mortality, especially cardiovascular over 5 years
Explore the physiological and biochemical processes that enable humans to adapt to exercise. Learn how the body meets the oxygen and metabolic fuel needs of muscles during physical activity.
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