ArticlesMotor unit synchronization of the vasti muscles in closed and open chain tasks
Section snippets
Participants
Five volunteers (3 men, 2 women; mean age ± standard deviation [SD], 30±3.3y) participated in the study. Subjects were included if they had no history of knee pain or pain elsewhere in the lower limb and were excluded if they had any neurologic disorder. The study was approved by the Institutional Medical Research Ethics Committee and all procedures were conducted in accord with the Declaration of Helsinki.
Electromyographic activity
Electromyographic recordings were made from single motor units in the VMO by using a
Results
When subjects extended their knee against resistance in both the open and closed chain tasks there was a high degree of synchronization between motor unit firing in the medial and lateral vasti muscles. Table 1 shows the percentage of cases in which peaks were seen in the unrectified and rectified vastus lateralis averages, and the percentage of cases in which the power in the spectrum at the frequency of firing of the reference VMO motor unit was greater than 7.5%.
Discussion
Our findings in this study indicate that a high degree of synchronization exists between motor units in the medial and lateral vasti muscles during isometric knee extension efforts. Furthermore, the data indicate that the degree of common drive, although not leading to significantly greater near-simultaneous firing, may be greater in closed chain than in open chain tasks.
Conclusions
This study has shown a greater degree of coupling between the medial and lateral vasti muscles during closed chain tasks. Because this may contribute to greater coordination between the muscles, it provides another logical rationale for using this form of exercise in the rehabilitation of patellofemoral pain.
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