Motor unit synchronization of the vasti muscles in closed and open chain tasks

doi:10.1016/j.apmr.2004.07.354

Archives of Physical Medicine and Rehabilitation

Volume 86, Issue 4, April 2005, Pages 716-721

https://doi.org/10.1016/j.apmr.2004.07.354 Get rights and content

Abstract

Mellor R, Hodges PW. Motor unit synchronization of the vasti muscles in closed and open chain tasks. Arch Phys Med Rehabil 2005;86:716–21.

Objectives

To investigate motor unit synchronization between medial and lateral vasti and whether such synchronization differs in closed and open chain tasks.

Design

Electromyographic recordings of single motor unit action potentials were made from the vastus medialis obliquus (VMO) and multiunit recordings from vastus lateralis during isometric contractions at 30° of knee flexion in closed and open chain conditions.

Setting

Laboratory.

Participants

Five volunteers with no history of knee pain (age, 30±3.32y).

Interventions

Not applicable.

Main outcome measure

The degree of synchronization between motor unit firing was evaluated by identifying peaks in the electromyographic averages of the vastus lateralis, triggered from motor unit action potentials in the VMO, and the proportion of power in the power spectral density of the triggered average at the firing frequency of the reference motor unit. The proportion of cases in which there was significant power and peaks in the triggered averages was calculated.

Results

The proportion of trials with peaks in the triggered averages of the vastus lateralis electromyographic activity was greater than 61.5% in all tasks, and there was a significantly greater proportion of cases where power in the spectrum was greater than 7.5% (P=.01) for the closed chain condition.

Conclusions

There was a high proportion of synchronized motor units between the 2 muscles during isometric contractions, with evidence for greater common drive between the VMO and vastus lateralis in closed chain tasks. This has implications for rehabilitation because it suggests that closed chain tasks may generate better coordination between the vasti muscles.

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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ArticlesMotor unit synchronization of the vasti muscles in closed and open chain tasks

Abstract

Objectives

Design

Setting

Participants

Interventions

Main outcome measure

Results

Conclusions

Section snippets

Participants

Electromyographic activity

Results

Discussion

Conclusions

J Neurosci Methods

Arch Phys Med Rehabil

Short-term synchronization of intercostal motoneurone activity

J Physiol

Synchronization of motor unit activity during voluntary contraction in man

J Physiol

The unilateral and bilateral control of motor unit pairs in the first dorsal interosseous and paraspinal muscles in man

J Physiol

Motor unit synchronisation is enhanced during slow lengthening contractions of a hand muscle

J Physiol

Motor unit discharge and force tremor in skill- and strength-trained individuals

Exp Brain Res

Effect of task on the degree of synchronization of intrinsic hand muscle motor units in man

J Neurophysiol

Organization of inputs to motoneurone pools in man

J Physiol

Functional coupling of motor units is modulated during walking in human subjects

J Neurophysiol

Electromyographic comparison of standard and modified closed-chain isometric knee extension exercises

J Strength Cond Res

The effect of patellar taping on the onset of vastus medialis obliquus and vastus lateralis muscle activity in persons with patellofemoral pain

Phys Ther

Articles
Motor unit synchronization of the vasti muscles in closed and open chain tasks