This article found that women with pain in the front of the knee have a muscle imbalance with the big muscle on the outside of the leg being stronger than the muscle on the inside. Good thing there are treatments for this type of issue with the knee. ~ Dr. Broussard
Vastus Lateralis Motor Unit Firing Rate Is Higher in Women With Patellofemoral Pain
Alessio Gallina, MSc, Michael A. Hunt, PhD, Paul W. Hodges, PhD, S. Jayne Garland, PhD
May 2018 Volume 99, Issue 5, Pages 907–913
Abstract
Objective
To compare neural drive, determined from motor unit firing rate, in the vastus medialis and lateralis in women with and without patellofemoral pain.
Design
Cross-sectional study.
Setting
University research laboratory.
Participants
Women (N=56) 19 to 35 years of age, including 36 with patellofemoral pain and 20 controls.
Interventions
Not applicable.
Main Outcome Measures
Participants sustained an isometric knee extension contraction at 10% of their maximal voluntary effort for 70 seconds. Motor units (N=414) were identified using high-density surface electromyography. Average firing rate was calculated between 5 and 35 seconds after recruitment for each motor unit. Initial firing rate was the inverse of the first 3 motor unit interspike intervals.
Results
In control participants, vastus medialis motor units discharged at higher rates than vastus lateralis motor units (P=.001). This was not observed in women with patellofemoral pain (P=.78) because of a higher discharge rate of vastus lateralis compared with control participants (P=.002). No between-group differences were observed for vastus medialis (P=.93). Similar results were obtained for the initial motor unit firing rate.
Conclusions
These findings suggest that women with patellofemoral pain have a higher neural drive to vastus lateralis but not vastus medialis, which may be a contributor of the altered patellar kinematics observed in some studies. The different neural drive may be an adaptation to patellofemoral pain, possibly to compensate for decreased quadriceps force production, or a precursor of patellofemoral pain.