Comparison Between Eccentric Hamstring Training and Sprint-Specific Training

Prior to the intervention, participants will undergo baseline testing which will include a) ultrasound imaging of the hamstrings muscles for measures of biceps femoris long head fascicle length, pennation angle, muscle thickness, anatomical cross-sectional area, and muscle volume b) passive and active ranges of motion, c) 3 repetition maximum (3RM) RDL strength, d) peak NHE force, e) countermovement jump height, f) broad jump distance, g) Pro Agility change of direction, and h) a 60 m sprint with sprint kinematics assessed via inertial measurement units.

Participants will be randomly assigned to either the RDL, NHE, or sprint training group. After randomization, each participant will undergo the intervention program based upon their group allocation.

Performance testing and imaging will be repeated mid-intervention, following the intervention, and after 2 weeks of deloading.

• RDL (Other): The RDL will be performed with a 6 second eccentric component with the athlete returning to the start position with a maximal concentric hip extension.
• NHE (Other): The NHE will be performed with a 6 second eccentric component.
• Sprint testing (Other): The sprint training program will be performed twice per week with the first day of training focused on shorter distances to focus on acceleration and the second training day focused on maximal velocity. The relative efforts and distances for each training day will mimic a similar prescription to that of the resistance training program.

Primary outcomes

• Change in fascicle length (FL) [Baseline to Mid-intervention (6 weeks), Post-intervention (10 weeks), and Post 2 week de-training (12 weeks)]
• Change in muscle cross-sectional area (CSA) [Baseline to Mid-intervention (6 weeks), Post-intervention (10 weeks), and Post 2 week de-training (12 weeks)]
• Change in muscle volume [Baseline to Mid-intervention (6 weeks), Post-intervention (10 weeks), and Post 2 week de-training (12 weeks)]
• Change in pennation angle (PA) [Baseline to Mid-intervention (6 weeks), Post-intervention (10 weeks), and Post 2 week de-training (12 weeks)]

Secondary outcomes

• Change in eccentric strength [Baseline to Mid-intervention (6 weeks), Post-intervention (10 weeks), and Post 2 week de-training (12 weeks)]: Eccentric hamstring strength of each limb will be assessed during the hamstring exercise.
• Change in inertial measurement units (IMU)-based sprinting biomechanics [Baseline to Mid-intervention (6 weeks), Post-intervention (10 weeks), and Post 2 week de-training (12 weeks)]: Sprinting biomechanics will be assessed using seven IMUs (sacrum, both thighs, both shanks, both feet). Lower extremity joint motions referenced to upright stance will be calculated throughout an on-field sprint and other football drills.
• Change in countermovement jump (CMJ) performance [Baseline to Mid-intervention (6 weeks), Post-intervention (10 weeks), and Post 2 week de-training (12 weeks)]
• Change in standing broad jump (SBJ) performance [Baseline to Mid-intervention (6 weeks), Post-intervention (10 weeks), and Post 2 week de-training (12 weeks)]
• Change in change of direction (CoD) performance [Baseline to Mid-intervention (6 weeks), Post-intervention (10 weeks), and Post 2 week de-training (12 weeks)]
• Change in range of motion (ROM) performance [Baseline to Mid-intervention (6 weeks), Post-intervention (10 weeks), and Post 2 week de-training (12 weeks)]
• Change in hip flexion [Baseline to Mid-intervention (6 weeks), Post-intervention (10 weeks), and Post 2 week de-training (12 weeks)]
• Change in anterior pelvic tilt [Baseline to Mid-intervention (6 weeks), Post-intervention (10 weeks), and Post 2 week de-training (12 weeks)]

Sex: All, ages: 18 Years to 25 Years, accepts healthy volunteers

Inclusion Criteria:

* Age 18-25 years
* Actively participating in a club team
* >6 months experience with resistance training
* Minimum of 1 year experience at the high school level in organized team sport
* No history of hamstring injury within the last 6 months
* No history of major lower extremity surgery (including back)
* No acute musculoskeletal injury to the lower extremity
* Not currently pregnant

Exclusion Criteria:

* Unable to refrain from resistance training outside the study
* Unable to make at least 80% of the training sessions
* Hamstring injury in the last 6 months
* History of major lower extremity surgery (including back)
* Acute musculoskeletal injury to the lower extremity
* Currently pregnant