When I went to massage school in 2001, science, and especially research, was far from my mind. My science knowledge and research awareness broadened a bit during massage school with my first exposure to anatomy and physiology and the research covered in Mosby’s Fundamentals of Therapeutic Massage, which at the time was primarily studies from the Touch Research Institute at the University of Miami and other related scientific concepts. It wasn’t until I began my doctoral training in 2006 that I got a true grasp of the depth and breadth of general research. I began devouring any and all massage-related, peer-reviewed, scientific articles. Those of particular interest were the ones covering theoretical and mechanistic underpinnings of massage therapy.
Moyer’s seminal 2004 review and meta-analysis of extant massage research had recently been published at the start of my doctoral training.1 At the time, I was struck by which massage therapy–related theories I was taught during massage school were missing in the then-current massage research. Those I felt were missing included, but were not limited to, trigger point “deactivation,” the neurological-based Law of Facilitation, and Pflüger’s Law of Symmetry.2 Interested to understand and test these theoretical mechanisms of massage effects, much of my research (all inspired by and devised post-Moyer’s 2004 review) is designed around and discusses these “missing” theoretical constructs. However, the extent to which my and others’ clinical research can isolate and measure the mechanistic aspects of these theoretical pathways are challenged; foundational work is needed in the basic science/bench research realms (bench research tends to refer to experiments conducted in “wet lab” settings on nonhuman subjects). This issue’s Somatic Research column focuses on just such recent research using an animal model that highlights massage’s impact via Pflüger’s Law of Symmetry or, as described in the article, the crossover effect. The clinically meaningful issue examined in this bench research is muscle atrophy and the potential for massage to enhance muscle regrowth.
“Enhanced Skeletal Muscle Regrowth and Remodelling in Massaged and Contralateral Non-Massaged Hindlimb” was published in the January 2018 issue of The Journal of Physiology.3 Given the journal’s discipline and nature of the research, the article may not be one massage therapists will generally access or learn about. Due to this work’s potential impact on the massage therapy field, I want to be sure therapists and educators learn of and understand this work’s results and value. Here, I provide a brief review of the study’s methodology and results followed by massage education and practice implications and suggestions.
Study Overview and Results
Cyclic compressive loading (CCL) applied via a computer-driven device is the massage mimetic used in the study. Essentially, the CCL device supports an anesthetized animal while its limb with the muscle of focus is secured and rhythmically “massaged” by a pneumatically driven wheel, which controls determined shear and compressive forces.4 The CCL delivery device was used so treatment application could be standardized—a feat challenging for human-administered massage. The study examined the gastrocnemius muscles of rats and used a randomized controlled experimental design.
At the start of the experiment, 32 10-month-old rats were randomized to one of four groups (eight in each group).
1. Weight bearing: rats were allowed to move and exercise freely. This was essentially the experiment’s control group, with no induced atrophy.
2. Hindlimb suspension: muscle atrophy was induced by suspending rats’ hindquarters for 14 days, becoming the experiment’s atrophy-only control.
3. Reambulation: after 14 days of hindlimb suspension, rats were allowed to reambulate/move and exercise freely for seven days.
4. Reambulation plus massage: same as reambulation group, with 30 minutes of standardized (load and frequency) CCL applied over the gastrocnemius muscle every other day starting on reambulation day 1 (four total bouts).
The experiment ended after 14 days for rats in groups 1 and 2 (weight-bearing and hindlimb-suspended control groups) and after 21 days for rats in groups 3 and 4 (reambulation and reambulation plus massage groups). At the end of the experiment, rats were euthanized and measured aspects (intracardiac blood, gastrocnemius muscles, and femur bone marrow) were harvested for testing.
The outcomes and measures used in the research were at cellular and cellular component (e.g., DNA, RNA, and specific proteins) levels and are different from those I usually discuss and work with (e.g., those measured at the system or person level). Muscle size measures, along with muscle cell signaling components and aspects involved with protein synthesis, were measured in the study and compared at the end of the experiment.
Study Analysis
The first step of this study’s analysis was to confirm that muscle atrophy did occur for rats in groups 2–4. Comparisons of the gastrocnemius muscles of rats in the control (weight bearing) and atrophy-only (hindlimb suspension) groups confirmed atrophy occurred, with average muscle fiber cross-sectional area decreasing by 38 percent. Because the rats in groups 3 and 4 experienced hindlimb suspension the same as those in the atrophy-only group, we can assume atrophy occurred for these rats similarly even though they were not measured immediately after atrophy inducement (that is what the rats in the atrophy-only group were for).
Here’s where it gets exciting: rats in the reambulation group did not experience a significant regrowth response in the gastrocnemius muscle compared to the atrophy-only group. However, those in the reambulation plus massage group had significantly larger muscle fibers compared to the atrophy-only and rehabilitation groups. In addition, muscle size also increased significantly in the nonmassaged gastrocnemius muscle in the reambulation plus massage rats compared to the reambulation rats, indicating a crossover effect occurred. Let this information sink in a little bit.
This research indicates that cyclic compression load, an animal mimetic for massage therapy, can enhance muscle regrowth directly (on the immediate muscle addressed) and contralaterally (the same muscle on the other side of the body). While the exact cell-signaling mechanisms through which these outcomes occur are still unknown, this research points to increased muscle size due to increased protein synthesis at both the myofibrillar (the actual muscle fibers making up the sarcomeric lattice) and cytosolic (fluid cell component) levels. Protein degradation, the targeting and elimination of damaged or faulty proteins within a cell, was also elevated in the reambulation plus massage rats, which the authors point to as contributing to enhanced protein synthesis.
Implications for the Massage Therapy Field
We do not yet know what force is ideal or at what “dose” massage administration is necessary for human muscle, or at which level of atrophy. However, the principle that rhythmic sheer and compression administered to muscle through massage has the potential to enhance muscle regrowth on not just the applied but opposite limb is huge and can be applied to a large variety of general and trademarked massage techniques and in countless situations. For example, many people are in situations every day in which muscle atrophy is induced. Whether due to an accident, functional decline, illness, or recovery necessity, people are in situations in which their muscles are immobilized or cannot be used, and atrophy can set in. This is particularly concerning for those working with the elderly population because of atrophy’s role in the cyclical relationship of functional decline and falls/fear of falling and link to increased mortality risk.
The opposite limb and crossover aspect of this work is particularly intriguing and my expectation to see Pflüger’s Law of Symmetry applied in massage research is finally met, even though the actual term is not used. In essence, this crossover effect, or Pflüger’s Law of Symmetry, states that if the right amount of force is applied to the muscle on one side of the body, the neurological impulse to produce the same effect will cross over to the other corresponding muscle.
In practice, I have always thought of this and applied it in my treatment planning when faced with a situation in which I was unable to directly address an area in direct need. While I didn’t necessarily apply the concept with the intention to enhance muscle regrowth, growth, or otherwise, I did apply the concept with the intent for the work’s benefit to transfer to the corresponding area on the other side of the body. For example, when my friend called me concerned about her husband’s excruciating cramps in his casted leg, I advised her to assist him to stretch and massage his other leg in the areas that were giving him trouble. This approach was very helpful for him and provides anecdotal support to this theoretical approach to massage application.
It is incredibly important that the massage therapy field cite and apply this study’s results appropriately. For example, it would not be appropriate for a massage therapist to claim, based on this study (or any other study for that matter), that a particular massage technique or session they provide will regrow muscle or reduce muscle atrophy. This research does not prove that massage therapy reduces or reverses muscle atrophy in humans. There are still a lot of questions that need answering about the mechanisms this study’s results occurred through, as well as application specifics regarding human delivery and treatment receipt for human muscles. However, this work does provide exciting evidence to support similar massage therapy benefit in humans. Massage therapists and educators can also point to this research to highlight massage therapy’s potential role in functional health support for humans, including rehabilitation populations.
I look forward to the future work examining massage therapy’s mechanistic pathways and the clinical human studies this work is sure to inspire. I will do my best to keep readers posted!
Notes
1. C. A. Moyer, J. Rounds, and J. W. Hannum, “A Meta-Analysis of Massage Therapy Research,” Psychological Bulletin 130, no. 1 (2004): 3–18.
2. D. G. Simons, J. G. Travell, and L. S. Simons, Travell & Simons’ Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 1: Upper Half of the Body, 2nd ed. (Baltimore: Williams & Wilkins, 1998); Segen’s Medical Dictionary, “law of facilitation,” accessed May 2018, https://medical-dictionary.thefreedictionary.com/law+of+facilitation; Mosby’s Dictionary of Complementary and Alternative Medicine, ed. Wayne B. Jonas, “Pfluger’s law of symmetry,” accessed May 2018, https://medical-dictionary.thefreedictionary.com/Pfluger%27s+law+of+symmetry.
3. B. Miller et al., “Enhanced Skeletal Muscle Regrowth and Remodelling in Massaged and Contralateral Non-Massaged Hindlimb,” The Journal of Physiology 596, no. 1 (January 2018): 83–103.
4. T. A. Butterfield et al., “Cyclic Compressive Loading Facilitates Recovery After Eccentric Exercise,” Medicine and Science in Sports and Exercise 40, no. 7 (2008): 1289–96; C. Waters-Banker, T. A. Butterfield, and E. E. Dupont-Versteegden, “Immunomodulatory Effects of Massage on Nonperturbed Skeletal Muscle in Rats,” Journal of Applied Physiology 116, no. 2 (January 2014): 164–75.
Niki Munk, PhD, LMT, is an assistant professor of health sciences at Indiana University, a Kentucky-licensed massage therapist, a visiting fellow with the Australian Research Centre in Complementary and Integrative Medicine, and mother of two young daughter-scientists. Munk’s research explores real-world massage therapy for chronic pain, trigger point self-care, massage for amputation-related sequelae, and the reporting and impact of massage-related case reports. Contact her at nmunk@iu.edu.