BWH Clinical & Research News

Downward-Facing Rat? How “Rat Yoga” Is Unraveling the Mystery of Back Pain

Dennis Munoz Vergara, DVM, PhD, of the Osher Center Connective Tissue Lab, carefully lifts a rat out of its cage and brings it over to the stretching station at his lab bench. After placing the rat on a platform that looks like an overturned box, he lifts the rat by the tail, off its hind legs, and coaxes the rat to grab onto the edge of the platform with its front paws. Vergara starts a timer set for 10 minutes and holds the rat in this position that elongates and stretches its entire back. The rat doesn’t make a sound as it holds its pose, occasionally moving its front paws to different areas of the platform edge. Helene Langevin, MD, director of the Osher Center for Integrative Medicine, refers to this experimental procedure as “rat yoga.”

Langevin has studied back pain for many years. While physicians often look at the spine, discs between vertebrae and nerves as the culprit of back pain, Langevin focuses on fascia — a type of connective tissue.

“Fascia is a really interesting part of the body that people haven’t paid much attention to. It’s the tissue that connects everything,” said Langevin.

When inflammation arises in the fascia, it creates pain and limits mobility. Recently, Langevin’s research has centered on the role that stretching and physical manipulation of this tissue can play in treating back pain.

Langevin first began using rats to study yoga while working at the University of Vermont in 2012. A student interested in yoga and the effects of stretching on back pain and inflammation found that rats and mice naturally grab onto the surface in front of them when lifted by the tail, making them a great fit for studying the effects of stretching. Langevin’s lab also found that this stretch increased the length between the rodent’s shoulders and hips by 25 percent and made for a perfect way to study the effects of stretching on back tissue.

Over the course of several studies examining “rat yoga,” Langevin has found a number of interesting results. In her experiments, researchers inject a chemical called carageenan into the rat’s back fascia to create local inflammation. The rats then undergo two 10-minute sessions of continuous stretches per day for two weeks before she and her team examine the rats. Rats are prepared for the stretching measurements by shaving the back, cleaning the skin and drawing a midline for measurements.

In these experiments, researchers have observed smaller inflammatory lesions in the fascia of stretched rats compared to non-stretched rats. They have also found fewer macrophages (immune cells that contribute to inflammation), decreased pain sensitivity and improvements in the gait of stretched rats.

In another study, Langevin and her colleagues looked at the way stretching affects systemic sclerosis (SSc), an autoimmune disorder characterized by the thickening and scarring of the body’s connective tissue. In this experiment, mice with sclerodermatous graft-versus-host disease, a disease that mimics SSc, underwent the same stretching regimen for four weeks. At the end of the experiment, the mice that had stretched had decreased skin thickness and increased subcutaneous tissue mobility compared to the mice that did not undergo the stretching regimen.

After uncovering the anti-inflammatory and preventive benefits of stretching, Langevin examined the possible mechanism for how these changes in fascia occur. While attending a lecture about the resolution of inflammation by Charles Serhan, PhD, director of BWH’s Center for Experimental Therapeutics & Reperfusion Injury, Langevin wondered if perhaps stretching set in motion the body’s natural healing response to inflammation. Langevin examined the rat tissues and found resolvins — naturally occurring lipid-based molecules that help resolve inflammation after injury. Her lab, in collaboration with Matthew Spite, PhD, of the BWH Department of Anestesiology, Perioperative and Pain Medicine, and Serhan, found higher levels of resolvins in the stretched tissues compared to the non-stretched tissues.

The Future

Langevin hopes to expand her research to look at differences in male-versus-female stretching response, optimal stretching times and how over-the-counter anti-inflammatory medicines might impede the success of stretching as treatment.

However, the ultimate goal is to perform these kind of tests with people to understand how stretching can alleviate human back pain. But that is no easy task. In “rat yoga,” the researcher stretches the rat in a controlled setting, and being lifted by the tail may help the rat relax its back muscles while it is stretched. It would be challenging to mimic that strain in humans who may have difficulty holding the stretching pose while staying relaxed.

Though she hasn’t yet studied this kind of stretching in humans, Langevin’s research makes clear the importance of lifestyle and behavioral changes in alleviating pain.

“If we knew how powerful lifestyle changes really are, I think we would pay more attention to them,” said Langevin. “Our goal is to create more awareness among the medical profession about these types of approaches; especially with the growing problems related to prescribing opiate and anti-inflammatory drugs.  At the Osher Center, we try as much as possible to offer non-pharmacological options to patients, especially for chronic pain.”