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Related Concept Videos

Torque01:10

Torque

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Torque is an important quantity for describing the dynamics of a rotating rigid body. We see the application of torque in many ways in the world, such as when pressing the accelerator in a car, which causes the engine to apply additional torque on the drivetrain. Here, we define torque and provide a framework to create an equation to calculate torque for a rigid body with fixed-axis rotation.
Torque can be considered as the rotational counterpart to force. Since forces change the translational...
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Muscles that Move the Leg01:23

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The movement of the legs is facilitated by numerous muscles located within the anterior, medial, and posterior compartments of the thigh.
Anterior Compartment
The quadriceps femoris, the most visible muscle of the anterior compartment, is integral for leg extension and thigh flexion. It is formed by merging four distinct muscles — the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris. The quadriceps tendon, a shared tendon of the four quadriceps muscles, is affixed...
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Excitation-Contraction Coupling in Skeletal Muscles01:20

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Excitation-contraction coupling is a series of events that occur between generating an action potential and initiating a muscle contraction. It occurs at the triad, a structure found in skeletal muscle fibers that comprise a T-tubule and terminal cisternae of the sarcoplasmic reticulum on each side. These triads are visible in longitudinally sectioned muscle fibers. They are typically located at the A-I junction — the junction between the A and I bands of the sarcomere.
When an action...
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Net Torque Calculations01:19

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When a mechanic tries to remove a hex nut with a wrench, it is easier if the force is applied at the farthest end of the wrench handle. The lever arm is the distance from the pivot point (the hex nut in this case) to the person’s hand. If this distance is large, the torque is higher. Only the component of the force perpendicular to the lever arm contributes to the torque. Therefore, pushing the wrench perpendicular to the lever arm is more advantageous. If multiple people apply force to...
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Motor Unit Stimulation01:20

Motor Unit Stimulation

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When the neuron of a motor unit fires an action potential, it triggers a series of events, leading to a twitch contraction in the muscle fibers. The process of excitation-contraction coupling is crucial in relaying the action potential to the muscle fibers.
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...
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Angle of Twist: Problem Solving01:13

Angle of Twist: Problem Solving

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An electric motor applies a torque of 700 N·m to an aluminum shaft, triggering a stable rotation. Two pulleys, B and C, are subjected to torques of 300 N·m and 400 N·m, respectively. The modulus of rigidity is provided as 25 GPa. With the knowledge of the length and diameter of each segment, the twist angle between the two pulleys can be computed. First, a section cut is made between pulleys B and C, and the cut cross-section is analyzed using a free-body diagram. Given that the torque...
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Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations
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Do changes in neuromuscular activation contribute to the knee extensor angle-torque relationship?

Marcel B Lanza1, Thomas G Balshaw1, Jonathan P Folland1

  • 1School of Sport, Exercise and Health Sciences, Loughborough University, UK.

Experimental Physiology
|June 9, 2017
PubMed
Summary

Changes in quadriceps activation and hamstring coactivation influence knee extensor strength across different knee angles. This finding is crucial for understanding neural adaptations in training and rehabilitation.

Keywords:
interpolated twitch techniqueknee joint anglesurface electromyography

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Area of Science:

  • Neuromuscular Physiology
  • Biomechanics
  • Exercise Science

Background:

  • The relationship between knee extensor torque and joint angle is influenced by neuromuscular activation.
  • Previous research has yielded inconsistent findings due to varied methodologies in assessing muscle activation.

Purpose of the Study:

  • To compare neuromuscular activation of the quadriceps femoris during isometric maximal voluntary contractions (iMVCs) at various knee joint angles.
  • To investigate the contribution of agonist and antagonist muscle activation to the knee extensor angle-torque relationship.

Main Methods:

  • Utilized surface electromyography (sEMG) and the interpolated twitch technique (ITT) to measure quadriceps activation.
  • Assessed agonist activation and antagonist coactivation at four knee joint angles (25°, 50°, 80°, 106°).
  • Normalized EMG to maximal M-wave amplitude and calculated activation via ITT.

Main Results:

  • Quadriceps (agonist) activation decreased at more extended knee positions (80°, 106°) compared to flexed positions (25°, 50°).
  • Hamstring (antagonist) coactivation was highest at the most flexed position (106°).
  • Both agonist and antagonist activation patterns varied significantly with knee joint angle.

Conclusions:

  • Both agonist and antagonist muscle activation contribute to the knee extensor angle-torque relationship.
  • These findings have implications for optimizing training and rehabilitation strategies across different knee joint angles.