Muscle Health, Fatigue, and Disease Flashcards

Exercise and Muscle: Acute Effects

Muscle Fatigue

• Caused by:

  • Substrate Depletion: Glycogen stores in muscle cells become depleted during prolonged exercise, reducing the energy available for muscle contraction.

  • Damage to Muscle Fibers: Micro-tears in the muscle fibers occur during intense physical activity, leading to inflammation and pain.

  • Build-up of Metabolic By-Products: Accumulation of lactic acid and other metabolites can interfere with muscle contraction and contribute to the sensation of fatigue.

• Results:

  • Loss of force and function in the affected muscles, impacting performance.

Delayed Onset Muscle Soreness (DOMS)

• Occurs: 12-72 hours post-exercise, often more pronounced after eccentric exercises.

• Causes Include:

  • Muscle Fiber Damage: The extent of damage correlates with the intensity and duration of the exercise.

  • Oedema: Fluid accumulation in muscle tissues as a result of the inflammatory response can exacerbate soreness.

Exercise and Skeletal Muscle: Chronic Effects

Muscle Fiber Ratios

• Fast Glycolytic (FG) vs Slow Oxidative (SO) fibers:

  • Muscle fiber composition is genetically determined and influences athletic performance significantly.

  • Higher FG Proportion:

    • Ideal for activities that require short bursts of high energy, such as weight lifting and sprinting.

  • Higher SO Proportion:

    • Best suited for endurance activities, enabling sustained energy output over longer durations, as seen in long-distance running.

Effects of Different Types of Exercise

• Impact on Muscle Fibers: Various forms of exercise can induce changes in muscle fiber types and characteristics.

  • Endurance training, while promoting cardiovascular health, does not lead to an increase in muscle mass but may lead to improvements in endurance performance.

  • Aerobic training can convert some FG fibers into Fast Oxidative Glycolytic (FOG) fibers, enhancing both oxidative capabilities and power output.

Improved Metabolic Machinery

• Mitochondrial Changes:

  • An increase in both the size and number of mitochondria enhances energy production efficiency within the muscle cells.

• Enzymatic Changes:

  • The number of glycolytic enzymes, such as Glycogen phosphorylase, Phosphofructokinase, and Lactate Dehydrogenase (LDH), increase, enhancing the muscle's capacity for anaerobic energy production.

  • Additionally, oxidative enzymes, like Citrate synthase and Cytochrome C oxidase, also increase but do not necessarily improve efficiency.

Substrate Metabolism

• Fat Metabolism:

  • Training leads to increased fat oxidation at rest and during submaximal exercise, primarily due to enhanced blood flow to muscles and elevated mitochondrial function.

• Carbohydrate Metabolism:

  • Improved oxidation of carbohydrates during maximal exercise is attributed to greater mitochondrial capacity and enhanced glycogen storage capabilities.

Other Adaptations from Exercise

• Regulation of Ionic Balance: Regular exercise can improve the homeostatic mechanisms that manage ionic concentrations in cells, thus aiding contraction and overall muscle function.

• Neural Adaptations: Enhanced neural connectivity and motor unit recruitment improve coordination and muscle firing rates during exercise.

• Cardiorespiratory Adaptations:

  • With consistent exercise, there is increased capillarisation (the formation of new capillaries) which enhances oxygen and nutrient delivery to muscles and overall endurance.

Physiological Adaptations to Resistance Training

• System/Variable Responses:

  • Number of Muscle Fibers: Increase in total muscle fiber count due to muscle hypertrophy often seen in response to resistance training.

  • Size: Muscle hypertrophy leads to increased fiber size, although the response can be equivocal and varies among individuals.

  • Strength: Generally, strength increases as a direct result of hypertrophy and improved neuromuscular function.

  • Adenosine Triphosphate (ATP) and Phosphocreatine: Both nutrient concentrations increase, thereby enhancing immediate energy availability for high-intensity efforts.

  • Capillary Density: Changes in capillary density can vary, with some bodybuilders and power lifters showing different adaptations compared to endurance athletes.

  • VO2max: The maximum rate of oxygen consumption may decrease in some resistance-trained individuals compared to endurance-trained athletes.

  • Mineral Content and Density: Resistance training leads to improved mineral content and density within muscles, which contributes to overall muscle health.

Body Composition

• Lean Body Mass: Increases through consistent resistance training, benefitting metabolism and overall physical performance.

• Percent Body Fat: Typically decreases, reflecting improved body composition and health metrics.

Muscular Hypertrophy/Atrophy

Hypertrophy

• Mechanism: Hypertrophy occurs primarily through the enlargement of existing muscle fibers, which is the result of increased synthesis of myofibrils and organelles necessary for muscle contractility.

Atrophy

• Disuse Atrophy: A reversible condition that can occur due to inadequate physical activity, leading to muscle size reduction.

• Denervation Atrophy: A more severe condition resulting from nerve disruption, causing significant muscle size loss over time and potential permanent impairment.

Hypertrophy Considerations

• Pros:

  • A greater cross-sectional area of muscle fibers results in increased strength, positively impacting performance in various sports and activities.

• Cons:

  • Larger muscle mass can create a greater diffusion distance for nutrients and waste, potentially complicating recovery and performance.

Strength and Injury

• Study on Hamstring Injuries: Research indicates that a pre-season muscle imbalance serves as a considerable risk factor for injuries, highlighting the need for targeted training in injury prevention.

• Conventional H:Q Ratio: A ratio of less than 0.6 significantly increases hamstring injury risk, up to 17 times, emphasizing the importance of balanced training.

Exercises to Strengthen Hamstrings

• Hamstring Exercises Overview: Focuses on injury prevention and biomechanics, which is essential for athletes in high-risk sports.

• Examples of Exercises:

  • Nordic Hamstring Exercise: Maximally activates hamstring muscles through a controlled, knee-extending action, effectively strengthening the entire muscle group.

  • Loaded Lunge Box Drops: These exercises progressively increase strain through controlled single-leg movements, enhancing strength and stability.

  • Barbell Leg Curls: These promote hamstring strength effectively, should be included in any comprehensive resistance training program.

Muscle Disease Overview

• Tetanus:

  • Caused by the bacterium Clostridium tetani, which leads to involuntary muscle spasms due to neurotransmitter inhibition. Prompt recognition and treatment are crucial to prevent severe symptoms.

• Muscular Dystrophies:

  • A group of genetic disorders that result in progressive muscle degeneration and the replacement of muscle tissue with connective tissue, leading to loss of function.

• Distal Arthrogryposis:

  • Characterized by contractures of distal limbs and varying severity, requiring specialized management and treatment options to enhance function and mobility.

Summary of Skeletal Muscle Diseases

• Duchenne Muscular Dystrophy (DMD):

  • An X-linked genetic disorder marked by mutations in the dystrophin gene, leading to progressive muscle degeneration, particularly affecting boys and requiring ongoing medical care and support.