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Related Concept Videos

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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.
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Wave summation
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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.
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Related Experiment Video

Updated: May 7, 2026

Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations
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Longer electromechanical delay impairs hamstrings explosive force versus quadriceps.

Ricci Hannah1, Claire Minshull, Stephanie L Smith

  • 11Sport, Health and Performance Enhancement (SHAPE) Research Group, School of Science and Technology, Nottingham Trent University, Nottingham, UNITED KINGDOM; 2Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UNITED KINGDOM; 3School of Health and Life Sciences, Glasgow Caledonian University, Glasgow, UNITED KINGDOM; and 4School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UNITED KINGDOM.

Medicine and Science in Sports and Exercise
|October 16, 2013
PubMed
Summary
This summary is machine-generated.

Delayed hamstring activation impairs explosive force, increasing anterior cruciate ligament injury risk. This study quantifies the early hamstring-to-quadriceps force ratio, revealing critical deficits in neuromuscular performance.

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Area of Science:

  • Neuromuscular physiology
  • Sports biomechanics
  • Injury prevention

Background:

  • Explosive neuromuscular performance is crucial for rapid force generation.
  • Lower hamstring explosive force relative to quadriceps may increase anterior cruciate ligament (ACL) injury risk.
  • The time course of hamstring vs. quadriceps explosive force and their ratio is not well understood.

Purpose of the Study:

  • To investigate the time course of explosive force production in hamstrings and quadriceps.
  • To determine the explosive hamstrings-to-quadriceps (H/Q) force ratio during early activation phases.
  • To assess the impact of electromechanical delay (EMD) on H/Q force ratios.

Main Methods:

  • Assessed neuromuscular performance in 20 untrained males using isometric knee flexion/extension.
  • Recorded force and EMG for hamstrings and quadriceps during explosive and maximal voluntary contractions.
  • Calculated explosive H/Q force ratios and compared EMD between muscle groups.

Main Results:

  • Quadriceps force was significantly greater than hamstring force, especially in the early phase (0-50 ms) after activation.
  • Explosive H/Q force ratios were very low (0-17%) at 25-50 ms, differing significantly from maximal voluntary H/Q ratios (56%).
  • Hamstrings exhibited a 95% greater EMD than quadriceps, leading to a delayed onset of force production.

Conclusions:

  • Prolonged hamstring EMD significantly impairs early explosive force production relative to quadriceps.
  • This deficit in early hamstring force may compromise knee stability.
  • The findings suggest a potential mechanism for increased ACL injury risk during the critical initial phase of explosive movements.