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Muscles containing trigger points tire more easily

PainSci » bibliography » Ge et al 2012
Tags: muscle pain, exercise, etiology, muscle, pain problems, self-treatment, treatment, pro

PainSci commentary on Ge 2012: ?This page is one of thousands in the bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided wherever possible.

Ge et al. found a dozen health volunteers with one (latent, painless) trigger point in the trapezius muscle on one side, but not the other. Then they subjected them to a bit of a torture test: holding their arms up for as long as possible, with EMG needles stuck in their shoulders (EMG can measure muscle fatigue, with some caveats, see Cifrek, Arabadzhiev, González-Izal).

So, how long can you hold your arms straight out the sides? They did fairly well, about seven minutes, but it got uncomfortable. On a pain-scale of 10, the subjects rated the non-trigger point side just over a 2 … but much higher on the trigger point side, at about 6.5.

And the EMG results demonstrated that muscles with trigger points show clear signs of greater fatigability. Specifically and most importantly, the trigger point side showed significant decreases in mean power frequency, which correlates with muscle ischemia, or poor oxygenation (a suspected biological feature of trigger points).

These results suggest that muscle tissue around a clinically defined trigger point is different from other muscle tissue in an objectively verifiable way.

~ Paul Ingraham

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

OBJECTIVE: Muscle fatigue is prevalent in acute and chronic musculoskeletal pain conditions in which myofascial trigger points (MTPs) are involved. The aim of this study was to investigate the association of latent MTPs with muscle fatigue.

DESIGN: Intramuscular electromyographic (EMG) recordings were obtained from latent MTPs and non-MTPs together with surface EMG recordings from the upper trapezius muscles during sustained isometric muscle contractions in 12 healthy subjects.

OUTCOME MEASURES: Normalized root mean square (RMS) EMG amplitude and mean power frequency (MNF) were analyzed. The rate of perceived exertion and pain intensity from MTP side and non-MTP side were recorded.

RESULTS: Pain intensity on the MTP side was significantly higher than the non-MTP side (P < 0.05). Intramuscular EMG from latent MTPs showed an early onset of decrease in MNF and a significant decrease at the end of fatiguing contraction as compared with non-MTPs (P < 0.05). Surface EMG from muscle fibers close to latent MTPs presented with an early onset of the increase in RMS amplitude and the increase was significantly higher than that from non-MTPs at the end of sustained isometric contraction (P < 0.05).

CONCLUSIONS: A latent MTP is associated with an accelerated development of muscle fatigue and simultaneously overloading active motor units close to an MTP. Elimination of latent MTPs and inactivation of active MTPs may effectively reduce accelerated muscle fatigue and prevent overload spreading within a muscle.

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