WK 13: Skeletal Muscle Aspects of Fatigue
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Questions and Answers

According to Merton's classic experiment, where is the main site of fatigue?

  • Sarcoplasmic reticulum
  • The muscle (correct)
  • T-tubules
  • CNS and peripheral nerves

    • What is the major end cause of force loss in skeletal muscle during fatigue?

  • Inhibition of muscle contraction by metabolic bi-products
  • Depletion of ATP
  • Buildup of lactic acid
  • Progressive fall in Ca2+ release from the Sarcoplasmic Reticulum (correct)

    • What is the function of the t-tubules in muscle fibers?

  • To align with the intracellular Ca2+ store, the Sarcoplasmic Reticulum (correct)
  • To store lactic acid
  • To regulate Ca2+ release from the Sarcoplasmic Reticulum
  • To inhibit muscle contraction

    • What is the current status of the Lactic Acid Theory of muscle fatigue?

    <p>It has lost the support of the mainstream scientific community</p> Signup and view all the answers

    What is the mechanism by which Ca2+ release from the Sarcoplasmic Reticulum triggers skeletal muscle contraction?

    <p>It triggers skeletal muscle contraction</p> Signup and view all the answers

    What is a common consequence of excessive training?

    <p>Performance decline</p> Signup and view all the answers

    What is the purpose of 'tapering' in training?

    <p>To reduce fatigue before a big event</p> Signup and view all the answers

    What is a primary factor in muscle fatigue, according to the provided references?

    <p>Calcium ion release</p> Signup and view all the answers

    What is a key site of muscle fatigue?

    <p>Sarcoplasmic reticulum</p> Signup and view all the answers

    Which of the following is NOT mentioned as a mechanism of muscle fatigue?

    <p>Lactic acid accumulation</p> Signup and view all the answers

    What is the primary cellular process responsible for producing fatigue during sustained contraction activities?

    <p>Build-up of lactic acid in the muscle</p> Signup and view all the answers

    What is the main clinical implication of muscle fatigue in humans?

    <p>Increased risk of muscle injuries</p> Signup and view all the answers

    In which intra-muscular sites does fatigue typically occur during physical activities?

    <p>Skeletal muscle fibers</p> Signup and view all the answers

    What role does Ca2+ release play in muscle fatigue?

    <p>Disrupts excitation-contraction coupling</p> Signup and view all the answers

    According to the lactic acid theory of muscle fatigue, what is the primary reason for muscle fatigue?

    <p>Increase in the levels of lactic acid in the muscles</p> Signup and view all the answers

    What type of training program may improve fatigue resistance more effectively than an endurance training program?

    <p>Strength training</p> Signup and view all the answers

    What is the faster component of recovery from fatigue due to?

    <p>Reversal of metabolic changes</p> Signup and view all the answers

    What is believed to be an important cause of overtraining in many sports?

    <p>Delayed recovery from fatigue</p> Signup and view all the answers

    Which process is suggested to be damaged in the delayed recovery from fatigue?

    <p>Action potential</p> Signup and view all the answers

    What is likely to improve with a strength training program to increase muscle mass according to the text?

    <p>Fatigue resistance</p> Signup and view all the answers

    What is the primary source of energy during a 100 m sprint?

    <p>Breakdown of phosphocreatine</p> Signup and view all the answers

    What occurs when ATP is depleted in muscle cells?

    <p>Rigor mortis</p> Signup and view all the answers

    What is the purpose of creatine phosphate in muscle cells?

    <p>To directly recharge ATP stores</p> Signup and view all the answers

    What is the primary mechanism of fatigue during a 100 m sprint?

    <p>Depletion of ATP stores</p> Signup and view all the answers

    What is the duration of anaerobic glycogen breakdown in muscle cells?

    <p>2-3 minutes</p> Signup and view all the answers

    How does caffeine impact muscle fatigue based on the text?

    <p>Caffeine enhances Ca2+ release from the SR</p> Signup and view all the answers

    What is the main consequence of phosphate entering the SR in muscle cells?

    <p>Formation of calcium phosphate precipitate</p> Signup and view all the answers

    What is the cause of the type of muscle fatigue known as 'hitting the wall'?

    <p>Near final depletion of glycogen</p> Signup and view all the answers

    What is the effect of long-distance running on ATP levels based on the text?

    <p>Minimal change in ATP</p> Signup and view all the answers

    In which diseases is a loss of skeletal muscle tissue commonly observed?

    <p>Cancer, HIV, muscular dystrophy, and chronic kidney failure</p> Signup and view all the answers

    What is the outcome of decreased muscle mass in terms of force generation?

    <p>Decreased capacity to generate force</p> Signup and view all the answers

    What is the consequence of muscles working at a higher fraction of their maximal capacity?

    <p>Early fatigue development</p> Signup and view all the answers

    What is not affected in patients with decreased muscle mass?

    <p>Actual fatigue resistance of the muscle cells</p> Signup and view all the answers

    What is necessary for designing optimal treatment strategies for patients with decreased fatigue resistance?

    <p>A careful analysis of the muscle function</p> Signup and view all the answers

    What is frequently due to a general decrease in muscle force production?

    <p>Increased fatigue ability</p> Signup and view all the answers

    What is affected in patients with congestive heart failure?

    <p>Fatigue resistance and SR calcium handling</p> Signup and view all the answers

    What is associated with a loss of skeletal muscle tissue?

    <p>Cancer, muscular dystrophy, and other diseases</p> Signup and view all the answers

    Why do muscles always have to work at a higher fraction of their maximal capacity in patients with decreased muscle mass?

    <p>Due to decreased capacity to generate force</p> Signup and view all the answers

    What is a common feature of various diseases and conditions?

    <p>Loss of skeletal muscle tissue</p> Signup and view all the answers

    What is the primary source of energy during a 100 m sprint?

    <p>Phosphocreatine breakdown</p> Signup and view all the answers

    Why does the muscle have to rely on aerobic fat metabolism once glycogen is gone?

    <p>To keep muscle contracting for 30-60 minutes</p> Signup and view all the answers

    Which metabolic by-product is mentioned to produce fatigue?

    <p>Lactic acid</p> Signup and view all the answers

    What happens if ATP runs out in muscle cells?

    <p>Rigor mortis sets in</p> Signup and view all the answers

    What is a primary evolutionary pressure for the development of fatigue as a signaling mechanism for low ATP?

    <p>To enhance endurance</p> Signup and view all the answers

    What happens when an athlete overtrains and the slow phase of recovery is never completed?

    <p>A vicious cycle develops leading to performance decline</p> Signup and view all the answers

    In the context of muscle fatigue, what is the primary clinical implication for humans?

    <p>Decreased fatigue resistance</p> Signup and view all the answers

    Where does the text suggest muscle fatigue often occurs during physical activities?

    <p>Sarcoplasmic Reticulum</p> Signup and view all the answers

    What is the main consequence of excessive training leading to performance decline?

    <p>A decrease in muscle strength</p> Signup and view all the answers

    How do some athletes respond to the decline in performance caused by incomplete recovery?

    <p>By further increasing training</p> Signup and view all the answers

    What primarily contributes to the drop in force from skeletal muscle during fatigue according to the text?

    <p>Progressive fall in Ca2+ release from the Sarcolemma</p> Signup and view all the answers

    Where is the main site of fatigue in muscle according to the information provided?

    <p>At the A/I junction of the muscle fiber</p> Signup and view all the answers

    What is the current status of the Lactic Acid Theory of muscle fatigue according to the provided text?

    <p>Not supported by most scientists</p> Signup and view all the answers

    What cellular mechanism is responsible for muscle fatigue during sustained contraction activities according to the information provided?

    <p>Release of Ca2+ from the Sarcoplasmic Reticulum</p> Signup and view all the answers

    Which intracellular site closely aligns with the t-tubules and is related to muscle fatigue according to the text?

    <p>Sarcoplasmic Reticulum</p> Signup and view all the answers

    What is the main difference between the world record time for a 100m sprint and a 1000m race, as mentioned in the text?

    <p>The world record for the 1000m race is much longer than the 100m sprint.</p> Signup and view all the answers

    What is the primary characteristic of muscle fatigue in elite athletes during activities, according to the text?

    <p>Muscle fatigue is usually reversible and recovery occurs within the first hour.</p> Signup and view all the answers

    Which of the following best describes the characteristics of skeletal muscle fatigue as defined in the text?

    <p>It is the reversible decline of performance during activity</p> Signup and view all the answers

    What is the primary feature that sets the human body apart from machines like cars in terms of performance decline, according to the text?

    <p>The human body does not follow linear performance patterns like machines.</p> Signup and view all the answers

    What is the main implication of muscle fatigue in humans as discussed in the text?

    <p>Decreased performance in physical activities</p> Signup and view all the answers

    Study Notes

    Skeletal Muscle Aspects of Fatigue

    • Skeletal muscle fatigue is defined as the reversible decline of performance during activity, and most recovery occurs within the first hour.
    • Muscle fatigue is a complex phenomenon that depends on the type of activity.

    Cellular Mechanisms of Fatigue

    • The build-up of metabolic bi-products due to high rates of ATP utilization inhibits contraction.
    • The major end cause of the force loss is that Ca2+ release from the Sarcoplasmic Reticulum progressively falls.
    • The site of fatigue is in the muscle, with a smaller contribution from the CNS and peripheral nerves.

    Intra-Muscular Sites of Fatigue

    • The t-tubules invaginate into the fiber (cell) twice a sarcomere at the A/I junction.
    • The t-tubules are closely aligned with the intracellular Ca2+ store, the sarcoplasmic reticulum.

    ATP Sources and Fatigue

    • Free ATP is enough to power contraction for 2-3 seconds.
    • If ATP runs out, rigor (mortis) occurs, which would be an evolutionary pressure on the development of fatigue as a signaling mechanism for low ATP.
    • Muscle has several backup sources of ATP production, including:
      • Creatine phosphate, which directly recharges ATP and lasts for 20-30 seconds.
      • Glycogen, which can be broken down anaerobically (lasting for 2-3 minutes) or aerobically in the mitochondria (lasting for 30-60 minutes).
      • Aerobic fat metabolism, which is slow but has large stores.

    Fatigue in Different Activities

    • 100m sprint: fatigue is less of a problem due to the short duration, but there is still some fatigue and the maximum running speed occurs after about 60m.
    • 5km race: events last 10-15 minutes and are performed at close to the maximum capacity of the muscles, involving both aerobic and anaerobic ATP pathways.
    • Marathon: fatigue develops suddenly, known as "hitting the wall", and correlates with the near-final depletion of glycogen in muscles.

    Clinical Implications of Fatigue

    • Numerous disorders, such as cancer cachexia, inflammatory diseases, sepsis, burns, and muscular dystrophy, are associated with a loss of skeletal muscle tissue.
    • Decreased muscle mass results in decreased capacity to generate force, leading to early fatigue development.
    • Patients with congestive heart failure also show a decrease in fatigue resistance, which is due to defects in skeletal muscles.

    Recovery from Fatigue

    • The faster component of recovery is due to the reversal of the metabolic changes that caused fatigue, and is completed in minutes.
    • The slower component of recovery takes several days and is likely caused by reduced Ca2+ release.
    • Overtraining can lead to a vicious cycle of declining performance, and tapering of training is a common practice to avoid this.

    Tapering and Training

    • With too much training, the slow phase of recovery is never completed, and performance can start to decline.
    • Athletes may respond to this decline by training even more, leading to a vicious cycle.
    • Tapering of training is a common practice to avoid overtraining and allow for recovery.

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    Skeletal Muscle Aspects of Fatigue - YR1 Lecture 1H 2022

    Description

    Test your knowledge on the mechanisms responsible for the drop in force from skeletal muscle during fatigue. This quiz is based on a classic experiment by Merton in 1954, involving simultaneous mechanical and electrical responses from the adductor pollicis muscle.

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