Hamstring Architectural and Functional Adaptations Following Long vs. Short Muscle Length Eccentric Training

Area of Science:

• Sports Medicine
• Exercise Physiology
• Biomechanics

Background:

• Standard eccentric exercises like Nordic hamstring curls do not fully replicate the hamstring's elongation stress during sprinting.
• The late swing phase of sprinting involves greater hamstring elongation than typically achieved in common preventive exercises.

Purpose of the Study:

• To investigate the effects of a 3-week eccentric resistance program on hamstring architectural and functional parameters.
• To compare adaptations between training performed at long muscle length (LML) and short muscle length (SML).

Main Methods:

• Participants completed eight sessions of maximal eccentric knee extensions using an isokinetic dynamometer.
• The SML group trained at 0° hip flexion, while the LML group trained at 80° hip flexion.
• Hamstring fascicle length, pennation angle, optimum contraction angles (concentric and eccentric), and peak torques were measured using ultrasound imaging and the dynamometer.

Main Results:

• Fascicle length increased significantly in both groups, with a larger increase in the LML group (9.3%) compared to the SML group (4.9%).
• Eccentric peak torque increased in both SML (12.9%) and LML (17.9%) groups.
• The LML group showed a greater tendency for decreases in concentric (17.3°) and eccentric (10.7°) optimum angles compared to the SML group.

Conclusions:

• Eccentric exercise training induces significant architectural and functional adaptations in the hamstrings.
• Training at longer muscle lengths (LML) may promote greater fascicle elongation and changes in optimal contraction angles.
• Further research is needed to confirm the superiority of LML eccentric training for hamstring adaptations.