Adaptations to Physical Activity

• Basic adaptations to physical activity (exercise physiology) involve developing a basic understanding of adaptations due to physical activity and connecting these adaptations to health outcomes.

Physical Activity

• Physical activity refers to any bodily movement produced by the contraction that results in a substantial increase in energy expenditure(above REE).
• The increase in energy expenditure must be significant enough to elicit health benefits.
• Exercise physiology involves the study of how physical activity affects the body's systems.

Exercise Physiology and Adaptations

• Adequate physical activity imposes stress, causing physiological systems to respond.
• In response to frequent physical stress, physical, neural, and biochemical adaptations occur to make physical activity more efficient.
• Acute and chronic adaptations improve the ability to perform physical work, leading to health benefits.
• Removal of physical stress results in the reversal of these adaptations (deconditioning).

Muscle Contraction and ATP

• ATP (Adenosine Tri-Phosphate) serves as the immediate energy source for muscle contraction.

Steps in Muscle contraction

• Myosin cross-bridge attaches to the actin myofilament.
• ATP is split into ADP and P, causing the cocking of the myosin head.
• The myosin head pivots and bends, pulling the actin filament to the M-line (working stroke); ADP and inorganic phosphate are released.
• As new ATP attaches to the myosin head, the cross-bridge detaches.

ATP Production

• ATP comes from the intake of food, including proteins, complex carbohydrates, and triglycerides.
• Amino acids come from proteins.
• Glucose is derived from complex carbohydrates.
• Fatty acids and glycerol are derived from triglycerides.
• Glycogen is stored in the liver and skeletal muscles.
• Muscle tissue cannibalization (starvation response) can also provide energy.
• Catabolic reactions break down molecules (ATP ADP + P).
• Anabolic reactions synthesize molecules (ATP PPP).
• ATP production is crucial for energy production and the breakdown of stored fat (during weight loss).

Aerobic ATP Production

• Aerobic ATP production needs oxygen.
• The citric acid cycle, with its various intermediates (e.g., pyruvate, acetyl-CoA, citrate), is essential for aerobic ATP production.

Review Questions

• Adaptations to physical activity occur to improve efficiency and respond to stress.
• Actin and myosin are the main proteins that interact to facilitate muscle contraction.
• The primary source of fuel for muscle contraction is ATP.
• ATP results from the breakdown of food sources like carbohydrates, fats, and proteins.

Chronic Adaptations in Skeletal Muscle for Aerobic Training

• Increased myoglobin enhances oxygen transport.
• Increased mitochondria improve energy production.
• Increased capillary density increases oxygen delivery.
• Increased stores of glycogen provide more fuel.
• Oxidative use of glycogen is enhanced.
• Increased stores of triglycerides allow for more fat utilization.
• Oxidation of fats is increased.

Muscle Fiber Types

• Type I (slow oxidative) fibers have high myoglobin, many mitochondria, and fatigue slowly; they are red and narrow.
• Type IIa (fast oxidative-glycolytic) fibers are medium in myoglobin, mitochondria, fatigue speed, color (red), and diameter.
• Type IIb (fast-twitch glycolytic) fibers have low myoglobin, few mitochondria, fatigue quickly, are white, and have a wide diameter.

Energy Metabolism and Exercise Intensity

• Aerobic metabolism requires oxygen and primarily oxidizes fat at low intensities.
• Aerobic metabolism at higher intensities oxidizes glucose and produces some lactic acid (LA).
• Anaerobic metabolism, without oxygen, produces extreme LA through glycolysis; examples include ATP-PC.

Muscle Fiber Recruitment

• Oxidative (aerobic) Type I fibers are recruited during walking.
• IIA fibers for jogging
• Type IIB (glycolytic/anaerobic) fibers are recruited during sprinting.
• Force and fatigability increase with the recruitment of faster fiber types.
• Fibers recruited dependant on force and fatigue, from low to high intensity.

Review of Muscle Contraction and Energy Sources

• All muscle contraction requires ATP.
• At low exercise intensities, ATP comes from fat oxidation.
• As exercise intensity increases, glycogen begins to break down.
• During high-intensity exercise, ATP is produced anaerobically.
• Accumulation of lactic acid increases.
• The body responds to energy demand/physical activity by various adaptations.

Study Guide Questions

• The human species adapts to physical activity to improve efficiency and survival.
• Muscle contraction's primary fuel source is ATP, developed from food sources.
• Muscle fiber types include Type I, Type IIa, and Type IIb, differing functionally in speed, force, and fatigability.

Learn about basic adaptations to physical activity related to exercise physiology. Explore how physical stress leads to physical, neural, and biochemical adaptation. Understand the impact of these changes on physical work and overall health benefits.