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Trigger Point Causes and Methods of Release

The existence of Trigger Points seems to be accepted by most practitioners of therapies directed at muscle pain relief. Although there are some practitioners that say they donít exist. They use the idea that trigger points have not yet been fully explained as some evidence of this position. Most medical research seems to be focused on how to make athlete's muscles perform at their peak, and what makes them fail, but little clinical research seems to have been conducted on the chemistry/biology of how regular people use muscles to failure. Additionally, most clinical restoration therapies are geared towards an athlete returning to competition (i.e. exercises to strengthen some muscle group), but it is difficult for most people to follow a physical therapy regimen, after all, most people aren't looking to return to competition, they just want to live without constant pain. The following theory makes a case for the existence of trigger points as well as how manual manipulation can restore proper function. The Sliding Filament theory will be used as a basis for the discussion.

According to the Sliding Filament theory, muscle contraction consists of bundles of long chains of sarcomeres, each of which shortens in length a small amount. Many sarcomeres getting shorter in a controlled way leads to shortening (contraction) of the entire muscle. Each sarcomere contains a set of actin filaments and myosin fibrils that slide across each other and are held there by myosin heads attaching to binding sites on the actin based on an electrochemical signal sent from a motor neuron (action potential). The contraction begins with Calcium ions being released into the sarcomere, binding with Troponin, causing a shift of the Tropomyosin, revealing a binding site that the myosin head is strongly attracted to. The myosin head binds to the site, releasing ADP in a reaction with magnesium and a phosphate, bending the myosin at the same time, the bending causes the fibers to slide by each other (contract).  The continued sliding (contraction) or holding of a contracted position requires an ongoing chemical cycle requiring the use of energy (ATP). ATP breaks the bond of the myosin head to the actin and if a continued action potential is sent to the sarcomere, Calcium ions remain available allowing the myosin head to re-attach to a binding site on the actin filament in order to hold or continue a contraction. Therefore energy (ATP) is required to return a muscle from the contracted state back to normal length. ATP must also be continuously synthesized in the muscle for the contraction to continue. Eventually ATP and other high energy phosphates are depleted and the muscle becomes fatigued. In a fatigued muscle, with no ATP available, the mitochondria will remove the calcium, allowing the tropomyosin to obscure the binding sites on the actin, and the muscle returns to a flaccid condition, and must be rested. This type of fatigue is caused by repetitive summed muscle stimulation called tetanic stimulation.

What causes trigger points:
Trigger Points occurring in slow twitching, type I, muscles are caused by over-use of the muscle. The body attempts to do all it can to maintain the contraction of a muscle that may, as far as the body knows, be preventing certain death by allowing the person (or other animal) to maybe pull and hold themselves in a tree to get away from an attacker. After the danger is gone the muscle is damaged (or has triggerpoint(s)) but will repair itself if given a chance to rest. Hopefully the creature we are talking about doesnít have to perform life saving over-use of muscles on a daily basis. In modern times, muscle over-use may not be because of a life threatening situation, but the muscles will still perform as if it were if they are told to do so. The over-use command may come from the need to hold oneís arm up on the steering wheel of a car, or maybe the use of a computer keyboard and mouse - the reason the Pressure Pointer was created.

Considering the Sliding Filament model, perhaps muscles have a mechanism to hold a contraction without the requirement of ATP?  In certain types of muscle fibers, myosin heads can be relatively permanently bonded to actin filaments, instead of the ATP hungry myosin binding/releasing cycle that must occur for muscles to remain easily and quickly controlled. This state of actomyosin cross links could be caused by the calcium ion pump, the mitchondria, (or some other mechanism) to be instructed to not pump calcium out of the sarcomere in the absence of ATP. If calcium is made available without ATP, uncontrolled muscle contraction occurs and this is what happens to large numbers of fibers or sarcomeres in a particular muscle fiber. The body wide condition of a saturation of calcium in the sarcomere and the absence of ATP is what occurs in death, itís called rigor mortis. Localized, uncontrolled, relatively permanent, non-energy using contractions are trigger points. Trigger points are created in muscles that must remain contracted for very long periods of time without rest. Some of these muscles are commonly used to support the neck and shoulder joints.

What releases Trigger Points:
Although the pain of trigger points can often be reduced by the use of pain killing drugs, trigger points can be returned to normally functioning muscle fiber by manual manipulation, or sometimes just a lot of rest and some stretching. The degree to which a muscle is 'cramped' (the number of dysfunctional sarcomeres) is directly related to how strongly the muscle will try to remain that way, so trigger points that were caused by carrying luggage on a trip may be relatively easy to release if treated quickly, but if not treated, the trigger points may grow to include adjacent sarcomeres, or cause referred pain to other areas that are affected by the dysfunctional muscle fibers and may result in years of pain.
In general, there are three things that can be used in combination to return the sarcomeres to proper function, or, release trigger points; water, stretching and pressure. Under-hydration is one of the things that can cause chemical processes in the body to be less efficient. Proper hydration will help reduce the development of trigger points and make them easier to treat. Mechanically removing the stuck myosin heads from there binding sites (stretching) is the main means for the body to begin the process of returning the sarcomeres to proper function, applying pressure at the same time can greatly increase the effectiveness of the stretch by mechanically inducing the removal of calcium, hydrolyzing ATP and replenishing other phosphates to the muscle cells. Trigger points that have existed for extended periods, sometimes years, can be difficult to return to normal function and may require months of stretching and pressure treatment to fully restore function, and more importantly for most people, stop the pain.

Gary Turell Ė March 2006

 

 

References:

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookMUSSKEL.html

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html

http://fig.cox.miami.edu/~cmallery/150/neuro/muscle.htm

http://web.indstate.edu/thcme/mwking/muscle.html

http://labs.ansci.uiuc.edu/meatscience/Library/contraction%20and%20relaxation.htm

 

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