Relationship Between Eccentric Hamstring Strength and Passive Muscle Stiffness
Condition: Hamstring Injury
Study type: Interventional

Summary: 
      Ninety male subject will be divided into three group: a younger group (18-22y), an older
      group (30-40y) and a control group (18-40y). The study comprises 3 phases. PHASE 1: baseline
      strength and stiffness measurements of the hamstring muscles, PHASE 2: 12 week Nordic
      Hamstring strength training program (not for the control group) and PHASE 3: final strength
      and stiffness measurements. The aim of this study is twofold, namely to investigate (1)
      whether there is a difference in baseline stiffness of the hamstring muscle complex between
      different age categories and (2) the evolution of hamstring muscle stiffness during an
      eccentric strength training program within the different age groups. These two research
      questions could ultimately lead to a possible answer on the question if the higher
      probability of HSI (=hamstring strain injury) in the older age category with the lowest
      levels of eccentric hamstring strength could be due to an age-related difference in hamstring
      stiffness.
    

Detailed description: 
      Ninety male subjects will be equally allocated, according to their age, to either the younger
      NHE (Nordic Hamstring Exercise) group (aged between 18 and 22 years), the older NHE group
      (aged between 30 and 40 years) or the control group (aged between 18 and 40 years old).
      Potential candidates will be excluded from this study if they have a history of hamstring
      injuries, or a recent severe trauma or surgery in the lower extremity. All participants must
      perform at least 1 hour of weekly sport participation and do not participate in more than 3
      training sessions a week. To ensure valid measurements of eccentric strength and muscle shear
      modulus, subjects will be instructed not to engage in strenuous training or sport activities
      48 h prior to testing. All participants will be informed regarding the aim, content and
      possible risks associated with the experimental approach before they will be asked to sign an
      institutionally approved informed consent document, indicating voluntary participation in
      this study. Prior to the first training session, participants will undergo both a bilateral
      isokinetic eccentric and concentric strength protocol and an ultrasound elastographic
      assessment of the hamstring muscles to determine baseline strength (eccentric and concentric)
      and shear modulus of the posterior thigh muscles, respectively. Participants will be
      instructed not to engage in strenuous training or sport activities 48 h prior to testing to
      ensure a valid measure of the hamstring muscle-tendon elasticity. After completion of all the
      pre-training assessments, participants in the NHE groups will be familiarized with the
      correct execution-modalities of the eccentric hamstring exercise (NHE). For a period of 12
      weeks, both experimental groups will perform a progressive eccentric strength training
      program targeting the hamstring muscles, solely consisting of the NHE. On the other hand, the
      control group will be instructed not to engage in any lower limb strength training. After
      completing the final training session, hamstring eccentric strength and shear modulus of all
      participants will be reassessed. The isokinetic strength protocol will be systematically
      conducted after all shear modulus measurements have been finished in order to avoid acute
      influences of previous exertion on the elasticity measurements.
    

Intervention name(s): 12 week nordic hamstring exercise program
Intervention type(s): Other
Intervention description(s): 12 weeks progressive eccentric strength training program targetting the hamstring muscles.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Participant)
Primary purpose: Prevention
Keywords: Hamstrings; Stiffness; Strength; Shear wave elastography