Eccentric Training Effects on Hamstrings Structure, Strength, and Sprint Performance
Condition: Exercise Training; Sport; Running; Ultrasound Imaging; Elastography; Healthy
Study type: Interventional

Summary: 
      The overall goal of this study is to investigate the effects of a 6-week training program
      between two hamstring exercises-the Romanian deadlift (RDL) and the Nordic hamstring exercise
      (NHE)-on hamstring strain injury risk factors and sprint performance.
    

Detailed description: 
      Prior to the intervention, participants will report to the lab on one occasion for baseline
      assessments. During the baseline visit, a) regional measures of biceps femoris long head
      fascicle length, pennation angle, muscle thickness, and anatomical cross-sectional area will
      be determined using ultrasound, b) baseline NHE strength and 3RM for the RDL will be
      determined, and c) maximal 60 m sprint performance will be measured.

      Participants will be randomly assigned to either the RDL or NHE. After randomization, each
      participant will undergo the 6 week intervention program based upon their group allocation.
      Exercises will be performed using a 6 second eccentric (i.e., lowering) contraction.

      Following the 6 week intervention, participants would return to the lab for post-intervention
      assessments of regional hamstring morphology and architecture and sprint testing, which would
      be carried out in the same manner as baseline assessments. Since fascicle length changes are
      known to return to baseline values within 2 weeks after the cessation of eccentric training,
      participants will be asked to return to the lab following a 2 week detraining period where
      final imaging, strength, and sprint performance assessments will be determined.
    

Intervention name(s): Ultrasound imaging; Hamstring Eccentric Strength Testing; Maximal 60 m Sprint; Romanian Deadlift; Nordic hamstring exercise
Intervention type(s): Diagnostic Test; Other; Other; Other; Other
Intervention description(s): Ultrasound B-mode images will be unilaterally collected from the biceps femoris muscle of the dominant limb for each participant using a commercial ultrasound system and linear array transducer. Standardized image locations will correspond to 33%, 50%, and 67% of the thigh length from the ischial tuberosity.
Three repeat longitudinal extended-field-of-view images of the entire biceps femoris muscle will be collected for offline analysis for fascicle length, muscle thickness, and pennation angle. Transverse extended-field-of-view images will be captured at the proximal, mid-belly, and distal locations to determine regional anatomical cross-sectional area of the biceps femoris long head muscle.
To determine changes in tissue stiffness via ultrasound shear wave speed, the same transducer will be placed in the same locations in a longitudinal view. Shear wave maps will be generated by the ultrasound system and shear wave speed measures extracted from the middle of the map.; Prior to each test, participants will perform a standardized 5-minute general warm-up followed by a task-specific warm-up including 3 sets of submaximal trials. Load increases (5-20%) will be added for each RDL 3-repetition maximum trial attempt until the participant cannot complete 3 repetitions through the full range of motion using proper technique. A 3-minute rest will be administered between all warm-up and testing sets to allow for full recovery.
Participants will kneel on a commercial device used to assess maximum eccentric knee flexor strength via uniaxial load cells with their ankles secured into fixed hooks. Participants will slowly lower their torso to the ground with arms crossed across their chest and without bending at the hips or spine. The maximal test will consist of 1 set of 3 maximal repetitions. If participants can control lower themselves to the ground, then they will hold barbell plates (5-10 lb increments) across their chest while performing the NHE.; Following a standardized warm-up, inertial measurement units (IMUs) will be placed on the sternum, sacrum, and bilaterally on the thighs, legs, and foot. Each participant will perform a total of 3 maximal 60 m sprints from a standing position with 1.5-3 min rest in between each trial to minimize the effects of fatigue.; The RDL intervention will be performed twice per week for 6 weeks. Participants will hinge at the hips lowering the bar to just below their patella before reversing the movement. The RDL will be performed with a 6 second eccentric component and returning to the start position with a maximal concentric hip extension.; The NHE will be performed twice per week for 6 weeks. Participants will be instructed to maintain their ankles in a dorsiflexed position, lower themselves as close to the ground as possible at a constant and controlled speed while maintaining a neutral position of the hips and trunk, and to cross their arms in front of their chest.
Other intervention name(s): RDL; NHE
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: Each eligible participant will be block randomized (1:1 allocation) to either the RDL or the NHE intervention group
Masking: Double (Investigator, Outcomes Assessor)
Primary purpose: Other