Contralateral hamstring (biceps femoris) coactivation patterns and anterior cruciate ligament dysfunction

Area of Science:

• Biomechanics
• Orthopedics
• Sports Medicine

Background:

• Hamstring coactivation during knee extension is theorized to enhance anterior cruciate ligament (ACL) stability.
• This coactivation may counteract anterior tibial translation caused by quadriceps activity.
• Understanding hamstring activation patterns is crucial for assessing knee joint stability, particularly after ACL injury.

Purpose of the Study:

• To compare hamstring coactivation patterns between individuals with ACL dysfunction and uninjured controls.
• To investigate contralateral hamstring coactivation differences in subjects with ACL injury.

Main Methods:

• Five subjects with ACL dysfunction (INJ) and five uninjured (UNI) subjects participated.
• Maximal knee flexions and extensions were performed on an isokinetic dynamometer at 100°/s and 300°/s.
• Torque, angular displacement, and hamstring electromyographic (EMG) activity were simultaneously recorded and processed.

Main Results:

• No significant differences in torque were observed between injured and uninjured limbs or between right and left limbs in controls.
• Injured subjects demonstrated approximately double the hamstring coactivation in their uninjured limb compared to their ACL-injured limb during extension.
• Uninjured subjects showed no significant difference in hamstring coactivation between their right and left limbs.

Conclusions:

• ACL dysfunction is associated with significant asymmetry in hamstring coactivation during knee extension.
• The contralateral limb's hamstrings may attempt to compensate for the injured limb's reduced coactivation.
• This hamstring coactivation asymmetry may be a contributing factor to or a consequence of ACL dysfunction and knee instability.