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Questions and Answers
Which type of muscle fibers are specialized for repeated contractions over prolonged periods of time?
Which type of muscle fibers are specialized for repeated contractions over prolonged periods of time?
Type II fibers have a higher concentration of mitochondria compared to Type I fibers.
Type II fibers have a higher concentration of mitochondria compared to Type I fibers.
False
What is the primary source of energy for muscle contraction?
What is the primary source of energy for muscle contraction?
ATP
The heads of the myosin molecules form _________ that bind reversibly to actin filaments.
The heads of the myosin molecules form _________ that bind reversibly to actin filaments.
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Match the types of muscle fibers with their characteristics:
Match the types of muscle fibers with their characteristics:
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Which method is most suitable for estimating energy expenditure without needing a laboratory setting?
Which method is most suitable for estimating energy expenditure without needing a laboratory setting?
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Keto-acids are a major fuel for energy production during exercise.
Keto-acids are a major fuel for energy production during exercise.
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What is the largest component of daily energy expenditure in sedentary individuals?
What is the largest component of daily energy expenditure in sedentary individuals?
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Energy balance represents the difference between energy intake and __________.
Energy balance represents the difference between energy intake and __________.
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Match the energy expenditure methods with their characteristics:
Match the energy expenditure methods with their characteristics:
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Which component accounts for approximately 10% of energy expenditure from diet?
Which component accounts for approximately 10% of energy expenditure from diet?
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The average energy expenditure of intermittent sports is higher than continuous sports.
The average energy expenditure of intermittent sports is higher than continuous sports.
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What factor influences differences in resting metabolic rate among individuals?
What factor influences differences in resting metabolic rate among individuals?
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Cyclists and triathletes may require energy expenditures as high as __________ kcal/day.
Cyclists and triathletes may require energy expenditures as high as __________ kcal/day.
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Which of the following is NOT a limitation of using heart rate monitoring for estimating energy expenditure?
Which of the following is NOT a limitation of using heart rate monitoring for estimating energy expenditure?
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Inhaling ambient air is a characteristic of closed-circuit spirometry.
Inhaling ambient air is a characteristic of closed-circuit spirometry.
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What strategy can be used to maintain energy balance during the Tour de France?
What strategy can be used to maintain energy balance during the Tour de France?
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Energy intake exceeding energy expenditure results in a __________ energy balance.
Energy intake exceeding energy expenditure results in a __________ energy balance.
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Activity records primarily rely on which of the following methods?
Activity records primarily rely on which of the following methods?
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Study Notes
Skeletal Muscle Structure
- Sarcomeres are the smallest functional unit of muscle tissue, comprised of thin (actin) and thick (myosin) filaments.
- Myosin heads form cross-bridges with actin filaments, contracting muscles by bringing Z-lines closer together.
- ATP serves as the energy source, activating ATPase sites on myosin heads.
Muscle Fiber Types
- Type I fibers are slow, oxidative, and ideal for repeated low-force contractions over extended periods; they contain high mitochondria and capillaries.
- Type II fibers, including IIa (fast, oxidative-glycolytic) and IIx (fast, glycolytic), are suited for quick, intense contractions but have fewer mitochondria and weaker capillary supply.
- Muscle composition varies: elite marathoners may have ~20% Type II fibers in vastus lateralis, while elite sprinters may reach ~60%.
- Postural muscles consist predominantly of Type I fibers (>70%).
Energy Production (ATP)
- ATP is continuously regenerated during exercise through:
- Phosphocreatine hydrolysis.
- Anaerobic metabolism of glycogen or glucose.
- Aerobic metabolism of acetyl-CoA, primarily from carbohydrate and fat breakdown.
- Keto-acids from some amino acids can fuel oxidative metabolism but contribute minimally during exercise.
Spirometry and Oxygen Consumption Analysis
- Closed-circuit spirometry measures energy expenditure (EE) under resting conditions, showing decreased oxygen volume with consumption.
- Open-circuit spirometry compares inhaled air with exhaled air (Douglas Bag technique) to assess gas exchange during exercise.
- Breath-by-breath systems provide accurate EE assessments and frequent feedback but are primarily lab-based.
Respiration Chamber and Tracer Methods
- Respiration chambers accurately measure energy balance and gas exchange, used for controlled dietary studies.
- Doubly labeled water determines energy expenditure over days or weeks via isotope detection, though it's costly.
- Labeled bicarbonate provides a less expensive estimation of EE through changes in CO2 production.
Heart Rate Monitoring
- Heart rate (HR) correlates linearly with oxygen consumption during submaximal exercise, aiding in EE estimation.
- Rest-related movements can influence HR without impacting oxygen consumption.
Accelerometer and Activity Records
- Accelerometers detect body movements, estimating activity levels and energy expenditure, though they often underestimate actual EE. Triaxial devices are more effective than uniaxial.
- 24-hour activity records provide a rough EE estimation, but can be biased due to personal reporting inaccuracies.
Components of Energy Expenditure
- Resting metabolic rate (RMR) accounts for 60% to 75% of daily energy expenditure; varies by fat-free mass, age, gender, and genetics.
- Diet-induced thermogenesis contributes ~10% of energy expenditure from food digestion and metabolism.
- Thermic effect of exercise constitutes 15% to 30% of energy expenditure, increasing significantly in active populations.
Energy Balance
- Energy balance is the difference between energy intake and energy expenditure over days or weeks.
- Positive energy balance leads to weight gain, while negative energy balance results in weight loss.
Energy Expenditure in Sports
- Intermittent sports like tennis have lower average energy outputs due to short bursts of high intensity followed by recovery.
- Continuous sports like cycling and running require higher energy outputs with elite females needing >3000 kcal/day and males >4000 kcal/day.
Considerations for Energy Intake in Endurance Events
- Athletes in events such as the Tour de France face challenges in energy intake during competition; significant refeeding occurs post-event.
- Gastrointestinal issues complicate absorption of large calorie volumes during intensive training.
Extreme Energy Expenditures
- High energy expenditures can reach 8,600 kcal/day for cross-country skiers and 10,750 kcal/day for ultraendurance runners without weight loss, provided intake matches expenditure.
- Historical expeditions (e.g., Scott and Shackleton) illustrate extremes, with significant weight loss due to limited energy intake despite high energy expenditure (~1,000,000 kcal over the expedition).
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Description
Explore the structure of skeletal muscle in Chapter 3, focusing on sarcomeres as the fundamental units of muscle contraction. This quiz delves into the interaction between actin and myosin filaments, as well as the role of ATP in muscle contraction.
