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Related Concept Videos

Torque01:10

Torque

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...
Muscles that Move the Leg01:23

Muscles that Move the Leg

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 to...
Net Torque Calculations01:19

Net Torque Calculations

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 rotate...
Angle of Twist: Problem Solving01:13

Angle of Twist: Problem Solving

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 exerted...
Angle of Twist - Elastic Range01:13

Angle of Twist - Elastic Range

Consider a cylindrical shaft with a length denoted by L and a consistent cross-sectional radius referred to as r. This shaft undergoes a torque at the free end. The highest shearing strain within the shaft is directly proportional to the twist angle and the radial distance from the shaft axis. When the shaft behaves elastically, this shearing strain can be articulated using variables such as the applied torque, radial distance, the polar moment of inertia, and the modulus of rigidity. By...
Isotonic and Isometric Muscle Contractions01:22

Isotonic and Isometric Muscle Contractions

Two primary types of muscle contractions are isotonic and isometric, each serving unique functions and involving distinct mechanisms. Both isotonic and isometric contractions are integral to the body's complex system of movement and stability. Isotonic exercises contribute significantly to functional strength and movement, while isometric contractions are crucial for maintaining posture and joint stability.
Isotonic contractions
Isotonic contractions occur when a muscle changes length while the...

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Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations
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Effect of hamstring flexibility on isometric knee flexion angle-torque relationship.

J Alonso1, M P McHugh, M J Mullaney

  • 1Sports Physical Therapy Institute, Somerset, New Jersey, USA. clehance@ulg.ac.be

Scandinavian Journal of Medicine & Science in Sports
|April 4, 2008
PubMed
Summary

Hamstring flexibility impacts knee flexion strength. Less flexible hamstrings show increased torque at short muscle lengths and decreased torque at long muscle lengths, altering the angle-torque relationship.

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Area of Science:

  • Biomechanics
  • Kinesiology
  • Musculoskeletal Research

Background:

  • Hamstring flexibility is a key factor in lower limb biomechanics.
  • Understanding the relationship between hamstring flexibility and muscle strength is crucial for injury prevention and performance optimization.

Purpose of the Study:

  • To investigate the association between hamstring flexibility and the knee flexion angle-torque relationship.
  • To determine how variations in hamstring flexibility influence isometric knee flexion strength across different joint angles.

Main Methods:

  • Assessed hamstring flexibility in 20 participants using the straight leg raise (SLR) and active knee extension (AKE) tests.
  • Measured isometric knee flexion torque at five angles with specific thigh and trunk positioning.
  • Classified participants into 'tight' or 'normal' hamstring flexibility groups based on SLR and AKE results.

Main Results:

  • No significant difference in peak knee flexion torque between tight and normal hamstring groups (SLR P=0.82; AKE P=0.68).
  • The tight hamstring group exhibited peak torque at a greater knee flexion angle (shorter muscle length) compared to the normal group (SLR P<0.01; AKE P<0.05).
  • Tight hamstrings generated higher torque at shortest muscle lengths and lower torque at longer muscle lengths versus normal hamstrings (SLR P<0.001; AKE P<0.001).

Conclusions:

  • The angle-torque relationship for knee flexion is altered in individuals with less flexible hamstrings.
  • Reduced hamstring flexibility shifts torque production, increasing it at short muscle lengths and decreasing it at long muscle lengths.