This research examines the neurological control of shoulder abduction. To perform this movement the control system must monitor sensors in the muscles, ligaments, joints and so forth, then orchestrate the precisely coordinated and timed contraction and relaxation of the various muscles involved. This is done in such a way to produce smooth efficient movement, minimising the stress upon the various muscles and ligaments. More importantly, it helps controls the position of the head of the humerus so it is positioned properly in the glenoid fossa, spreading the load evenly across the joint and avoiding any impingement. This trial used surface electromyography (S-EMG) to investigate the effects of latent trigger points on this control. Trigger points are those tender lumps within tight bands of muscle that shoot pain when pressed upon. They are known as latent when not causing pain (only causing pain when pressed upon). S-EMG is is like the ECG used to monitor hearts, only it monitors nerve signals to muscles. Given that, the researchers investigated the following:
- How common latent trigger points were in the shoulder muscles of adults with no shoulder pain
- What was the effect of latent trigger points on the timing and coordination of muscle activity
- What effect does treating the trigger points have.
137 adult subjects were used for the trial. All had been pain free the previous week, had full shoulder movement and no obvious shoulder dysfunction or pathology.
What was done
Trigger point examination
The researchers first examined seven main muscles that control shoulder movement for trigger points. As the subjects were all pain free, trigger points found were by definition latent (asymptomatic) trigger points
Surface Electromyography (S-EMG)
During shoulder abduction the electrical signals sent to the muscles were monitored by surface electromyography (S-EMG). These are like the electrical sensors used with an ECG monitoring heart function, only the sensors are placed on muscles to detect nerve signals.
Trigger point examination
Of the 137 subjects
- Only 14 were found to be trigger point free.
- 123 (about 90%) had one or more trigger points.
- Nearly 80% of subjects had them in their upper trapezius, while five out of the six remaining muscles scored at least 60% in the same respect.
The effect on control
Surface EMG was used to investigate the coordinated timing of the seven muscles under investigation during shoulder abduction.
- The 14 subjects with no trigger points all showed a similar consistent pattern of muscle activation and timing.
- On the other hand those with trigger points showed differing orders and timing of activation
Effects of treatment
Those with abnormal muscle timing and activation due to trigger points were divided randomly into treatment and sham treatment groups. The sham treatment group received “ultrasound” with a non-functional machine. The treatment group had their trigger points treated using dry needling and stretching.
- Immediately following stretching the treated subjects were re-tested using the surface EMG. The activation patterns had become normal.
- The activation pattern for those receiving the sham treatment remained abnormal.
The fact that neurological control reverted back to normal once the trigger points were treated is very encouraging. Dr Lucas, the research scientist, did stress though that the effect was only measured very shortly after treatment, and that the long term effects were uncertain. As discussed in our research summary: Trigger Points: deactivation or elimination this is a serious concern. We raised the following points.
• According to a review of clinical trials investigating the treatment of trigger points the goal of trigger point treatment was to merely (temporarily) deactivate them.
• The three clinical trials that checked for the presence of trigger points after a series of therapy sessions found that the majority were still there.
• The way to totally eliminate trigger points would be to continue with treatments for a much longer period of time once asymptomatic. Due to cost and convenience, for most, self application with a vibration massager would be the only practical way to do this.
Prime consideration for musculoskeletal problems
Given the nearly 90% prevalence in asymptomatic people, trigger points would almost certainly be involved in any musculoskeletal pain pain syndrome. As well as their well recognised ability to refer pain this research shows they may cause pain indirectly by the alteration of biomechanics, creating extra stress upon various tissues. Further, if treating them just to the asymptomatic stage this research shown that they will still cause serious issues.
The prescription of exercises alone will not correct functional problems
Patients are often given exercises alone to remedy shoulder and other pain syndromes. This research shows however that this abnormal function is likely due to altered neurological control. Correction exercises will not change this. As shown by this and research the removal of the cause will correct this.
Regular screening and treatment of trigger points Trigger point therapy should be considered.
The subjects shown to have this problem were asymptomatic. Regular soft tissue therapy or a regular massage would arguably find and eliminate latent trigger points, thus preventing them from becoming active (painful) and causing abnormal function.
Everyone using a gym or exercising should be regularly screened for trigger points
Picture a person in a gym, asymptomatic but having trigger points in the muscles controlling shoulder joint movement. As he performs a bench press due to the alteration in control the head of the humerus does not sit normally in the glenoid fossa and several ligaments are under abnormal stress. On the 10th rep he feels sharp pain. This is what can happen when asymptomatic trigger points alter neurological control. Screening for trigger points would be even more important for those exercising.
_THE EFFECTS OF LATENT MYOFASCIAL TRIGGER POINTS ON MUSCLE ACTIVATION PATTERNS DURING SCAPULAR PLANE ELEVATION, by K.R. Lucas PhD.