Atividade elétrica dos músculos estabilizadores da patela em indivíduos portadores da síndrome da dor femoropatelar durante exercícios realizados no step.
Abstract
The purpose of this study was to evaluate the electric activity (EMG) in the temporal
and amplitude aspects of the vastus medialis obliquus (VMO), vastus lateralis longus
(VLL) and vastus lateralis obliquus (VLO) muscles during forward step tasks: stepdown
(SFD) and step-up (SFS), and backward step tasks: step-down (SPD) and step-up
(SPS). Twenty seven females were evaluated and separated in two groups: fifteen
normal subjects Control Group (21.13 ± 2.17 years) and twelve subjects with
Patellofemoral Pain Syndrome PPS (21.08 ± 2.31 years). The height of the step was
regulated for two angles 45º and 75º - of knee s flexion joint. A metronome was used to
help the volunteers about the time to performance the tasks, a eletrogoniometer was
used in the control of the knee angle and a pressure sensor was used to determinate the
start and the end of the electromyography register. The electric activity was recorded by
surface (Ag/AgCl) electrodes, an EMG apparatus with 8 channels (EMG System Brazil)
and a software of acquisition data AqDados 7.02. The EMG data was processed by the
software Matlab 6.1 that calculated both the onset timing of the muscles and the
integrated of the EMG signal. The EMG was normalized by the mean of the three
muscle contractions and was calculated de ratio VMO/VLL and VMO/VLO for
comparisons between groups and exercises. The relative onset timing was determinate
by the difference VMO-VLO and VMO-VLL. The t-tests showed that in the step up
exercise (75º of the knee flexion), there are differences when compared the groups,
either in frontal step VMO/VLL (p= 0.000) and VMO/VLO (p = 0.000), than posterior
step VMO/VLL (p = 0.000) and VMO/VLO (p = 0.000). In the control group there is a
prevalence of an early contractions of de VMO muscle, however in the PPS group, the
VMO onset occurred at the same time or after the VLO and VLL muscles in the mayor
of the cases. The Anova three-way and Duncan post hoc showed that in step at 45º, the
ratio VMO/VLO (p = 0,000) and VMO/VLL (p = 0,016) was greater then step at 75º in
both groups. When compared the steps in 45º and 75º into the groups, were found
differences either in the VMO:VLO ratio (p = 0,000) than VMO:VLL ratio (0,016) with
greater values in the step at 45º. The comparison between the exercises performed in the
same step height showed that both VMO:VLO and VMO:VLL ratios always was
greater in the SFS than SFD (p = 0,01), SPS (p = 0,04) and SPD (p = 0,000). There is no
difference between SFD and SPS (p = 0,570) or SPD (p = 0,090). In the Control group
the SPS was smaller then SPD, on the other hand, in the SDFP group the SPS was
greater than SPD (p = 0,30). Our results suggest that there is a difference in the motor
control between groups about muscle recruitment either in frontal than posterior step-up
at 75º. In the amplitude aspect, the step at 45º seem to recruit selectively the VMO
muscle in comparison with VLL and VLO, thus, this step height should be used
preferentially in the SDFP treatment programs. Regarding of the mode of execution, the
frontal step (SFS) seems to be the most indicated when the objective is the selective
activation of the VMO muscle mainly in the step at 45º.