Onset timing and strength between the vastus medialis obliquus and vastus lateralis during eccentric, isokinetic exercise
Open AccessBackgroundIn the sports medicine clinical setting, 25% of patients with knee related injuries are treated for patellofemoral pain syndrome (PFPS). PFPS is more prevalent in women than in men. Risk factors of interest are weakness of the vastus medialis obliquus (VMO) and delayed timing (i.e., a time lag when the muscle contracts) of the VMO compared with the vastus lateralis (VL). A number of investigators propose that a strength or timing deficiency in this medial quadriceps muscle prevents the patella from tracking correctly in the femoral trochlear groove, thus causing deterioration of structures such as the subchondral bone, retinacula, capsule, and synovial membrane, and thereby causing pain. Unfortunately, there is controversy in the literature as to whether or not this theory is valid. PurposeThe purpose of this cross-sectional study was to compare the strength ratio of the VMO:VL, as well as the activation timing of the two muscles at varying speeds (60°/sec and 300°/sec) during an isokinetic eccentric open kinetic chain exercise of the quadriceps in a population of asymptomatic female participants.ProceduresData for this analysis were collected from 13 asymptomatic female participants (mean height= 165.52cm, mean weight= 66.37kg, mean Q-angle= 20.15°). EMG activity of the dominant leg's VMO and VL was recorded during a maximal isometric hold and during eccentric, isokinetic, open kinetic chain testing at 60°/sec and 300°/sec with use of a Biodex. EMG data were collected using Noraxon EMG & Sensor Systems, recorded with amplitude normalization at a window of 1000ms. Noraxon MyoResearch XP Master Edition software determined mean onset times and peak strength activations.ResultsThe data failed to show a significant difference in the eccentric strength between the VMO and VL at 60°/sec [t(12)= -1.26, p= 0.23] and 300°/sec (s= -24.5, p= 0.09), VL at 60°/sec and 300°/sec [t(12)= 1.17, p= 0.27], and VMO at 60°/sec and 300°/sec [t(12)= 0.99, p= 0.34] in young, asymptomatic women. The data also failed to show a significant difference in the onset timing between the VMO and VL at 60°/sec (s= 9.5, p= 0.54) and 300°/sec [t(12)= -0.23, p= 0.82], VL at 60°/sec and 300°/sec (s= -7.5, p= 0.64), and VMO at 60°/sec and 300°/sec (s= -15.5, p= 0.31).Principal ConclusionsActivation timing and strength ratio of the VMO and VL should be determined in patients with PFPS to assess if a deficiency in the muscles is a contributing factor. As determined by this population of asymptomatic women, there should be no difference in VMO and VL onset timing at 60°/sec and 300°/sec and no difference in VMO:VL eccentric strength at 60°/sec and 300°/sec.
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