Latent Myofascial Trigger Points are Associated With an Increased Antagonistic Muscle Activity During Agonist Muscle Contraction
José Miota Ibarra, Hong-You Ge, Chao Wang, Vicente Martínez Vizcaíno, Thomas Graven-Nielsen, Lars Arendt-Nielsen - The Journal of Pain , Volume 12, Issue 12 , December 2011, Pages 1282–1288
http://www.sciencedirect.com/science/article/pii/S1526590011007632
Summary and Review by Brent Brookbush MS, PES, CES, CSCS, ACSM H/FS
Reasons Why the Study Was Performed:
The aim of the study was to investigate the effect of latent (non-symptomatic) motor trigger points on muscle activity in an antagonist muscles (opposing muscle) during agonist muscle contraction (isometric). In this case latent trigger points were evaluated in the posterior deltoid during isometric shoulder flexion at 25% of maximal voluntary contraction. This study demonstrated the occurrence of “altered reciprocal inhibition” due to the presence of motor trigger point involvement.
This study may also serve as a model for future researchers - the use intramuscular electromyography is paramount when studying this relationship; surface electromyography was insufficient in detecting increased motor unit (motor trigger point) activity.
The methodology that was employed:
This study included 14 health subjects. The level of activity within the muscles tested (the posterior deltoid) was measured using intramuscular electromyography (EMG). A needle was inserted into a latent motor trigger point (MTP) or a non-MTP at rest and during isometric shoulder flexion performed at 25% of maximum voluntary contraction. Surface EMG was also recorded on the anterior and posterior deltoid muscles. Maximal pain intensity and referred pain patterns were induced by the EMG needle inserted, and were recorded using a visual analogue scale. The results showed that higher local pain was observed following needle insertion into latent MTPs (4.64 ± .48 cm) than non-MTPs (2.35 ± .43 cm, P < .005). Referred pain was reported in 6 of the 14 subjects when the needle was inserted into a latent MTP, but none into the non-MTPs.
The results and conclusions of the investigators:
The intramuscular EMG activity, but not surface EMG activity, in the antagonist muscle was significantly higher at rest and during shoulder flexion at latent MTPs than non-MTPs. This study provides the first evidence that increased motor unit excitability is associated with reduced antagonist reciprocal inhibition.
Researchers perspective:
“This study shows that MTPs are associated with reduced efficiency of reciprocal inhibition, which may contribute to the delayed and incomplete muscle relaxation following exercise, disordered fine movement control, and unbalanced muscle activation. Elimination of latent MTPs and/or prevention of latent MTPs from becoming active may improve motor functions.”
This study is evidence to support several theories proposed by Human Movement Science professionals.
The occurrence of pain may be a poor indicator of dysfunction -
Dysfunction and alterations in motor unit recruitment may occur before the onset of pain. This was the case in 8 of the 14 subjects in this study who presented with latent trigger points, but no referral pain pattern.
Movement dysfunction and trigger points may result in “altered reciprocal inhibition” -
The presence of latent motor trigger points resulted in “increased antagonist muscle activity during agonist contraction” - the definition of altered reciprocal inhibition.
Trigger Point Release may improve recruitment patterns and performance -
Although this study did not specifically test the effectiveness of release techniques, it illustrates a reason for using these technique in symptomatic and non-symptomatic individuals. A reduction in antagonist muscle contraction may result in improved neuromuscular efficiency, optimal joint mechanics, and potentially, an increase in force production and performance.
A critique of the study with suggestions for further research
This study was well done; leaving little to be criticized. The subject pool was small, but consideration must be given for the invasive and painful methods employed in this study. Further research should look to replicate the results, and/or test another pair of functional antagonists using a larger group.
The muscles utilized may or may not be the best example of functional antagonists and yet the results still illustrated the hypothesis. Both the posterior and anterior deltoids are part of the deltoids muscle and share some common functions - abduction and approximation of the humeral head. Future research should look to test this hypothesis on other muscle pairing.
© 2012 Brent Brookbush
Questions, comments, and criticisms are welcomed and encouraged