Hamstrings Are Stretched More and Faster during Accelerative Running Compared to Speed-Matched Constant-Speed Running

Area of Science:

• Biomechanics
• Sports Medicine
• Athletic Training

Background:

• Hamstring injuries are prevalent in field sports, with high re-injury rates.
• Most research focuses on constant-speed running, neglecting accelerative mechanics.
• Understanding hamstring behavior during acceleration is crucial for injury prevention.

Purpose of the Study:

• To compare hamstring muscle-tendon unit lengths and lengthening velocities during accelerative versus constant-speed running.
• To investigate the biomechanical differences in hamstring loading between these two running conditions.

Main Methods:

• 10 participants performed accelerative and constant-speed running trials.
• 3D motion capture (OpenCap) and a musculoskeletal model estimated hamstring kinematics.
• Linear mixed models analyzed peak hamstring length and lengthening velocity.

Main Results:

• Accelerative running led to greater peak hamstring lengths and faster lengthening velocities compared to constant-speed running, especially below 75% of top speed.
• For instance, accelerating from 50% top speed induced hamstring lengths equivalent to constant 88% top speed running.
• Hip flexion kinematics were identified as the primary driver of these differences.

Conclusions:

• Hamstrings experience increased length and velocity during acceleration, offering a biomechanical explanation for injury occurrence.
• Coaches and medical staff should account for the accelerative component of running to better assess hamstring injury risk exposure.