Passive stiffness of the biarticular hamstring muscles could acutely decrease after eccentric-only resistance...

Area of Science:

• Biomechanics
• Muscle Physiology

Background:

• Understanding acute changes in muscle passive stiffness is crucial for optimizing training and injury prevention strategies.
• Biarticular hamstring muscles play a key role in locomotion and are susceptible to injury.

Purpose of the Study:

• To investigate the acute effects of passive stretching versus eccentric-only resistance exercise on the passive stiffness of biarticular hamstring muscles.
• To determine the influence of different exercise loads on these acute changes.

Main Methods:

• Thirteen healthy males underwent four exercise sessions: passive knee extension and eccentric knee flexion at 25%, 50%, and 75% of maximal torque.
• Measurements included range of motion, passive torque, muscle shear moduli (using shear wave elastography), and maximal isometric torque before and after each session.

Main Results:

• Passive knee extension did not significantly alter hamstring muscle shear moduli.
• Eccentric-only knee flexion significantly decreased muscle shear moduli immediately post-exercise at loads of 25-75%.
• Specific muscles like biceps femoris long head, semitendinosus, and semimembranosus showed load-dependent decreases in stiffness.

Conclusions:

• Eccentric contraction is more effective than passive stretching in acutely reducing hamstring passive stiffness.
• The exercise load necessary to decrease passive stiffness is dependent on the specific hamstring muscle and experimental conditions.