Lower extremity muscle activation and knee flexion during a jump-landing task

Area of Science:

• Biomechanics
• Sports Medicine
• Kinesiology

Background:

• Reduced knee flexion during dynamic tasks is linked to higher impact forces.
• This can elevate the risk of knee injuries, including anterior cruciate ligament (ACL) rupture.
• Understanding the interplay between muscle activation and knee motion is crucial for injury prevention.

Purpose of the Study:

• To investigate the relationship between lower extremity muscle activity and knee-flexion angles during jump landings.
• To identify specific muscle activation patterns associated with different knee-flexion strategies.

Main Methods:

• A cross-sectional study involving 30 healthy volunteers.
• Electromyography (EMG) measured lower extremity muscle activity (gluteus maximus, quadriceps, hamstrings, gastrocnemius).
• Knee-flexion angles (initial contact, peak, displacement) were recorded during jump-landing tasks.
• Correlation and regression analyses examined the relationship between muscle activity and knee kinematics.

Main Results:

• Greater activation of the vastus medialis obliquus (VMO), vastus lateralis (VL), and gluteus maximus (GMAX) correlated with smaller knee-flexion angles.
• Specifically, VMO, VL, and GMAX activity predicted significant variance in peak knee-flexion angle and displacement.
• A higher quadriceps to hamstring (Q:H) activation ratio was associated with reduced initial knee contact flexion.

Conclusions:

• Landing strategies characterized by greater quadriceps and GMAX activation and less hamstring/gastrocnemius activation are linked to reduced knee flexion.
• This 'stiff-legged' landing approach may increase knee joint impact forces.
• Further research is needed to confirm if this landing strategy directly contributes to knee injury risk.