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Intramuscular Hamstring Stiffness Affects Anatomically Modeled Localized Muscle Strain During Passive Hip Flexion.

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Intramuscular hamstring stiffness varies, with the proximal region being less stiff and experiencing greater strain during hip flexion. This stiffness variation may increase the risk of hamstring injuries, particularly those occurring in the proximal region.

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Area of Science:

  • Biomechanics
  • Musculoskeletal Research
  • Sports Medicine

Background:

  • Hamstring strain injuries are common and occur when localized tissue strain exceeds capacity.
  • Intramuscular variations in hamstring stiffness may influence localized muscle strain, but this area requires further investigation.

Purpose of the Study:

  • To investigate the impact of intramuscular hamstring stiffness on localized muscle strain during passive hip flexion.
  • To determine how stiffness differences within the biceps femoris, semitendinosus, and semimembranosus affect strain distribution.

Main Methods:

  • Utilized shear-wave elastography to measure hamstring muscle stiffness (biceps femoris, semitendinosus, semimembranosus) at proximal, medial, and distal regions.
  • Employed an anatomical model of equivalent springs, incorporating anthropometric and stiffness data, to estimate localized tissue strain.
  • Assessed stiffness during passive hip flexion and extension in 28 healthy adults.

Main Results:

  • Hamstring muscles exhibited lowest stiffness in the proximal region across shortened and stretched positions.
  • The proximal hamstring region contributed most significantly to passive strain (37.5-39.4%), with strain increasing during hip flexion.
  • Strain contribution was greater proximally compared to the middle (31.74-32.2%) and distal (28.6-30.3%) regions.

Conclusions:

  • Intramuscular variations in passive hamstring stiffness lead to inhomogeneous strain distribution within the muscle during passive hip flexion.
  • The higher proximal strain, coupled with lower proximal stiffness, may be a contributing factor to the high incidence of proximal hamstring strain injuries.