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Quadriceps force and myoelectric activity during flexed knee stance
A T Hsu1, J Perry, J K Gronley
1Pathokinesiology Service, Rancho Los Amigos Medical Center, Downey, CA 90242.
Clinical Orthopaedics and Related Research
|March 1, 1993
Summary
Quadriceps muscle demand increases significantly with knee flexion during single limb stance. This demand rises sharply above 30 degrees of knee flexion, impacting functional ambulation.
Area of Science:
- Biomechanics
- Human Physiology
- Kinesiology
Background:
- Understanding quadriceps muscle function is crucial for assessing knee joint stability and mobility.
- Single limb stance involves complex muscle activation patterns to maintain balance and control joint movement.
Purpose of the Study:
- To quantify quadriceps muscle demand during single limb stance across varying knee flexion angles (0-60 degrees).
- To investigate the relationship between knee flexion angle, quadriceps electromyogram (EMG) activity, and knee joint torque.
Main Methods:
- Ten healthy young adults performed single limb stance with knee flexion from 0 to 60 degrees.
- Intramuscular EMG recorded vasti muscle activity; an electrogoniometer measured knee angle.
- Knee flexion torque was determined using a visible vector system; patellar ligament force was calculated.
Main Results:
- Patellar ligament force increased linearly with knee angle (4.16% body weight per degree).
- Quadriceps force and normalized EMG showed strong correlations with knee angle (R²=0.91 and R²=0.88).
- Both quadriceps force and EMG increased more rapidly above 30 degrees of knee flexion.
Conclusions:
- Plantar flexor stabilization, changing muscle moment arms, and force ratios explain the non-linear EMG-force relationship.
- A critical knee flexion angle may exist, beyond which standing and ambulation become challenging.