Week 7: Muscle fatigue

Questions and Answers

What likely contributes more to muscle performance in vivo than electrical failure during maximal voluntary contractions?

Muscle mass

Neuromuscular junction efficiency

Electrical stimulation

Metabolic factors (correct)

Which of the following sources of ATP regeneration is used first during exercise?

Creatine phosphate (correct)

Aerobic respiration

Glycogen

Anaerobic respiration

During intense exercise, ATP concentration is typically maintained above what percentage of its initial value?

60% (correct)

75%

80%

50%

What differs significantly between in vivo and in vitro muscle contractions?

Tetanic force is less affected in vitro Signup and view all the answers

Which of the following metabolic processes can produce lactate as a byproduct?

Glycolysis Signup and view all the answers

What is the function of ATPase found in the myosin head?

Hydrolyze ATP Signup and view all the answers

What is the largest glucose store in the body?

Liver Signup and view all the answers

In working muscle, what happens to ATP concentration during exercise?

It remains fairly high Signup and view all the answers

What best characterizes muscle fatigue?

An exercise-induced reduction in the ability to produce maximal force. Signup and view all the answers

Which factor is NOT considered to influence muscle fatigue?

Metabolic rates in nearby organs. Signup and view all the answers

During Phase 1 of cellular fatigue in fast-twitch fibers, what occurs?

A quick decline in force alongside increased tetanic Ca2+. Signup and view all the answers

What mechanism occurs after the generation of a muscle action potential?

Activation of the voltage sensor Ca2+ channel (DHPR). Signup and view all the answers

In terms of task-dependence, muscle fatigue is influenced by what?

The muscle type and the nature of the physical task. Signup and view all the answers

Which of the following describes the concept of excitation-contraction coupling?

The sequence of events that converts an electrical signal into a mechanical contraction. Signup and view all the answers

What factor contributes to the variations in fatigue behavior among different muscles?

Type of muscle fibers in the muscle group. Signup and view all the answers

Which statement about muscle fatigue is accurate?

Loss of maximal voluntary contraction force is a sign of fatigue. Signup and view all the answers

Which group demonstrated a greater decline in maximum torque during the study?

Old males Signup and view all the answers

What was the mean maximum torque measured in the young group during the dorsiflexor muscle contractions?

38.3 ± 3.1 Nm Signup and view all the answers

In the submaximal contractions test, what was the average duration until task failure for the young group?

13.0 ± 5.2 min. Signup and view all the answers

What aspect of fatigue did young participants experience more quickly compared to old participants?

Surface EMG amplitude increase Signup and view all the answers

What was the sample age of the old group in the dorsiflexor experiment?

77.2 ± 1.4 years Signup and view all the answers

What similarity was found between both young and old during the submaximal contractions?

Torque reduction at failure Signup and view all the answers

In the study regarding strength-matched males and females, what was concluded about their maximum torque?

No difference in maximum was found Signup and view all the answers

Which factor was significantly higher in the young group during the submaximal contraction test?

Surface EMG amplitude Signup and view all the answers

What effect does an increase in Mg2+ have on myofibrillar sensitivity to Ca2+?

It reduces sensitivity to Ca2+. Signup and view all the answers

Which statement best describes the role of reactive oxygen species (ROS) in muscle cells?

ROS are mainly produced during oxidative metabolism and can react with various cellular components. Signup and view all the answers

What is a main consequence of fatigue on muscle shortening velocity?

ADP increase leads to reduced maximum shortening velocity. Signup and view all the answers

Which factor primarily contributes to the slowing down of muscle relaxation during fatigue?

Increased concentrations of ADP and Pi. Signup and view all the answers

What protective effect does Mg2+ provide to muscle cells during fatigue?

It limits Ca2+ release, thus preventing ATP depletion. Signup and view all the answers

Which substance has shown inconsistent effects on Ca2+ release in relation to muscle fatigue?

Reactive oxygen species. Signup and view all the answers

What is the primary mechanism by which fatigue induces muscle function impairment?

Elevated levels of ADP and hydrogen ions. Signup and view all the answers

What role do ROS scavengers have in muscle fatigue according to in vitro studies?

They can reduce fatigue by neutralizing reactive oxygen species. Signup and view all the answers

What characterizes Phase 1 of fatigue in fast-twitch fibers?

Quick decline in force and increased tetanic Ca2+ Signup and view all the answers

Which phase of fatigue displays a relatively constant force?

Phase 2 Signup and view all the answers

How can Phase 3 of fatigue be potentially reversed in isolated fibers?

Through pharmacological stimulation with caffeine Signup and view all the answers

What distinguishes fast-twitch fibers from slow-twitch fibers in terms of fatigue?

Fast-twitch fibers are easily fatigued Signup and view all the answers

Which of the following is true about extracellular K+ levels during exercise?

They can rise to 9 mM locally Signup and view all the answers

What is an effect of cyanide on muscle fibers in relation to oxidative phosphorylation?

Decreases the ability to perform oxidative phosphorylation Signup and view all the answers

What ion concentration is typically found in resting muscle fibers?

Intracellular K+ ~ 160 mM and extracellular K+ ~ 4 mM Signup and view all the answers

Which characteristic describes fast-twitch fibers during tetanic contraction phases?

They have a quick decline in performance in Phase 1 Signup and view all the answers

Study Notes

Muscle Fatigue Overview

Exercise-induced reduction in muscle ability to produce maximal force or power without complete task failure.
Fatigue is characterized by a decrease in maximum voluntary contraction (MVC) force, while submaximal force can be maintained.

Factors Influencing Fatigue

No single factor determines fatigue; numerous elements come into play.
Factors include:
- Intracellular components within muscle fibers
- Extracellular medium surrounding muscle fibers (e.g., changes in Na+, K+ levels)
- Peripheral nerves
- Central nervous system (CNS) contributions (spinal cord, brain)

Excitation-Contraction Coupling

Sequence of events:
- Nerve impulse triggers acetylcholine (ACh) release at the motor end plate.
- Muscle action potential is generated and propagated.
- Activation of calcium channels and subsequent release from the sarcoplasmic reticulum (SR).
- Calcium initiates cross-bridge cycling with ATP involvement.
- ATP is converted to ADP and inorganic phosphate (Pi).

Phases of Fatigue in Fast-Twitch Fibers

Phase 1: Quick reduction of 10-20% in force; increased tetanic Ca2+; reduced cross-bridge activity.
Phase 2: Maintenance of relative constant force, variable duration based on fiber type and oxidative capacity; continuous decay in whole muscle.
Phase 3: Rapid force decline; tetanic Ca2+ may be recovered with pharmacological agents like caffeine.

Fiber-Type Dependency

Fast-twitch fibers (easily fatigued) vs. Slow-twitch fibers (fatigue-resistant).
Fatigue behaviors vary significantly between different muscle fiber types.

Ionic Changes During Exercise

Resting muscle: High intracellular K+ (~160 mM) and low extracellular K+ (~4 mM).
During exercise, extracellular K+ can rise up to 9 mM locally, affecting muscle excitability.
Greater decline in force observed during continuous maximal voluntary contractions (MVC), while electrical stimulation can still elicit significant responses.

Metabolic Processes in Muscle

ATP serves as the primary fuel for muscle contractions; regenerated via:
- Creatine phosphate (CP)
- Glycogen stored within muscle fibers and the liver
- Utilization of anaerobic (lactate production) and aerobic (carbon dioxide generation) pathways.

Reactive Oxygen Species (ROS) in Fatigue

ROS production increases during oxidative metabolism.
Common types: superoxide, hydrogen peroxide, hydroxyl radicals.
ROS may target motor proteins and Na+/K+ ATPase, influencing muscle fatigue but lacking conclusive evidence for benefits of antioxidants in vivo.

Shortening Velocity and Relaxation

Fatigue reduces maximum shortening velocity primarily due to increased ADP levels.
Muscle relaxation is also slowed, influenced by increased ADP, Pi, and H+ levels.

Fatigue Reducing Mechanisms

Some mechanisms that impair muscle function may counteract fatigue.

Age and Fatigue Studies

Studies compare fatigue levels between young and older adults, revealing:
- Young individuals demonstrate greater strength and lesser torque decline than older individuals during contractions.
- Older adults exhibit a larger percentage decrease in max torque compared to younger counterparts.

Gender Differences in Fatigue

Strength-matched male and female participants show no significant differences in maximal fatigue responses during submaximal efforts, indicating comparable fatigue levels when normalized for strength.

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Description

This quiz covers the concept of muscle fatigue, focusing on its definitions, causes, and measurement methods. It discusses how fatigue affects maximum voluntary contractions and the various factors that contribute to exercise-induced fatigue. Learn about the differences between fatigue, task failure, and exhaustion.