Hamstring Muscle Architecture and Microstructure Changes Following 9-weeks of Nordic Hamstring Exercise Training

Motivation: Evaluate long-term muscle adaptations across the full volume of all four hamstrings in response to Nordic hamstring exercise (NHE) to enhance injury prevention strategies. Goal(s): Examine how 9-weeks of supervised NHE-training affects architecture (volume, fiber length, angle, and curvature) and microstructure (MD, RD, FA, and T2) of Biceps femoris short head (BFsh), Biceps femoris long head (BFlh), Semitendinosus (ST), and Semimembranosus (SM). Approach: 11 subjects underwent MRI scans (Dixon, DTI, and T2) pre and post 9-weeks NHE-training. Results: NHE-training increased hamstring volume with greater hypertrophy in ST and BFsh muscles. Hypertrophy was accompanied by increases in both length and cross-section of muscle fibers. Impact: This study examines architectural and microstructural adaptations of the hamstrings following 9-weeks of Nordic hamstring exercise training. Findings reveal significant, but non-uniform hypertrophy among hamstrings accompanied by increase in length and size of the muscle fibers, advancing injury prevention strategies.