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Massage Today
August, 2011, Vol. 11, Issue 08

Investigating the Physiology of Massage

By Massage Therapy Foundation Contributor

In this month's Massage Therapy Foundation Research Column, we are exploring how massage works on a physiological level. While massage has been shown to be effective in various settings - little is known about the mechanism of how massage produces its benefits.

It is commonly thought that at least some of the effects of massage come from alleviating muscle tension. However, it has yet to be conclusively shown to reduce the underlying neural activity (tone) in the muscle. Who hasn't asked or been asked, "Where are you experiencing tension today?" as Langdon Roberts asks in his article published in the March 2011 issue of the open access International Journal of Therapeutic Massage and Bodywork.

Langdon Roberts, MA, CMT, of the Center for Transformational Neurophysiology in Soquel, Calif., investigated this issue in a study entitled "Pressure Application and Resting EMG." Using surface electromyography (EMG) to measure muscle activity, Roberts hoped to quantify the exact change in muscle activity during two types of massage - light, medium and deep massage applied in the order of increasing pressure (IP) or decreasing pressure (DP). In this study, the electrical activity generated was measured in the m. rectus femoris of the left legs of twenty-five individuals. Roberts hypothesized that muscle activity would be lower after either massage, with IP resulting in significantly lower EMG activity than DP.

Roberts writes, "[When] Goldberg et al. compared light and deep petrissage to the triceps surae [...] deep massage produced a greater reduction in the H-reflex, an electrical analog of the stretch reflex." The H-reflex (Hoffman reflex) is a measure of spinal cord excitability. Roberts cites other research that appears to link a reduction in H-reflex and massage, although he notes H-reflex hasn't been linked to pain reduction or any other known benefits of massage.

Roberts used a clinical crossover design in this study, meaning all 25 individuals received both IP and DP massage, with at least four weeks in between. The ethics of Roberts' study protocol were approved by an internal review board at the Muscular Therapy Institute in Cambridge, Mass. The massage setup was simple, with electromyography electrodes placed proximally and distally to the left rectus femoris, at its musculotendinous junctions. Each massage session was composed of three strokes for each level of pressure to each leg's rectus femoris, beginning with the left leg.

Roberts solicited the three levels of pressure as: "light, but not insubstantial," "moderate" and "as deep as possible without causing pain or a sensation of increased muscle tension." Each slow stroke was performed in a toward-proximal direction and lasted for 15 seconds. Two minutes elapsed between each pressure level. The massage therapist wore thumbtip pressure sensors and applied the strokes using adjacent thumbs. These gloved sensors showed that people in the IP and DP group preferred different objective vs. subjective pressure levels as indicated in a repeated-measures ANOVA [p<0.02]. Further study may show that subjects who receive deep pressure first require a deeper objective pressure to get to a pressure subjectively on the border of pain. In other words, clients may be able to withstand deeper pressure when it is used first. Unfortunately, equipment malfunctions prevented a test of this hypothesis in this study; only 14 subjects had "reliable" data available for statistical analysis.

The EMG results, while surprising, confirm many massage therapists' intuition. Using repeated-measures ANOVA on a group with all DP data, Roberts found, "EMG varied significantly across the four time points [p < 0.03]." In the DP data the application of deep pressure without previous massage caused a sudden increase in muscle activity, which diminished when lighter pressure was later used. This was not the case with the IP group, where "IP data indicates that EMG did not vary significantly across the four times points [p = 0.71]." These results did not differ between the IP-first and DP-first groups [p = 0.30 & p = 0.38].

Although the individuals studied were mostly (>80%) women, this is typically true about the population that seeks massage therapy as well. Another limitation of the study is that different muscles may show different EMG results, since Roberts cites studies that show "a reduction of EMG activity after massage [...] consistently found only in the frontalis muscle." Notably, the massage in this study was applied only to the rectus femoris muscles that were already relaxed, not in pain or otherwise uncomfortable.

This study validates the use of EMG as a tool for investigating the physiological basis of massage. One potential subject for further study includes a comparison of the EMG methods used here - a MEDAC Sys/3 physiological monitor. Roberts recommends a system of "counting repeated minima during each collection period," which he suggests as superior to "counting mean values" because of the commonplace nature of EMG artifacts or false readings.

How can you apply the results of this study to your own practice? If your treatment goal is to reduce or minimize EMG activity, then you should begin with light pressure and gradually increase your pressure during effleurage strokes, especially on the large muscles of the quadriceps. Unfortunately, these results are limited to asymptomatic rectus femoris muscles studied in a small group of people by a single therapist. Further research may show that a DP style of massage consistently causes a sudden spike in EMG activity, and could relate that to patient outcomes. Research has not shown a link between EMG activity and subjective tension. According to Roberts, "Carlson et al. [found] no relationship between perceived tension and EMG activity in clients with muscle pain or in pain-free subjects." Roberts suggests it is likely that "multiple modulating factors" could be at play in the EMG results seen here.

The research reported here was funded by the Massage Therapy Foundation, the same foundation that supports this column. We hope Roberts' and others' research will elucidate to what extent endorphins, reflex pathways, and/or the "freeing of nociceptive or mechanoreceptive nerve endings" contribute to the physiological benefits of massage. For more information on the MTF, visit our website at www.massagetherapyfoundation.org/.

Source: Roberts, L. (2011). Effects of Patterns of Pressure Application on Resting Electromyography During Massage. International Journal Of Therapeutic Massage & Bodywork: Research, Education, & Practice, 4(1). Retrieved from www.ijtmb.org/index.php/ijtmb/article/view/25/154


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