A massage therapist applies warm compresses to a client's back.

Can we use heat during a massage session to benefit the client’s neuromuscular system? Of course.

Thermotherapy is comfortable when you are in pain, soothing like a weighted blanket. Heat can make you feel better before you feel better.

However, as comforting as it is, heat is not appropriate for every situation. It can speed up blood flow, which increases the speed of healing. That sounds pretty good; however, that sped-up blood flow can also create some serious tissue damage if used incorrectly. That is the quandary of thermotherapy. 

Heat works its wonders by vasodilation of the blood vessels. Vasodilation is the dilation, widening or opening of your vessels. That extra space allows for increases in blood flow, and that increased flow then creates an increased speed in everything from the metabolic breakdown of damaged tissue to the oxygenation and restoration of the cells. 

Let’s take a moment and look more deeply at how vasodilation occurs. The moment you place a hot pack on the skin, that increase in temperature begins to stimulate the thermoreceptors connected to the blood vessels.

That temperature increase results in the release of immune defense chemical mediators, like histamine, bradykinin and prostaglandins. The release of these mediators is part of the inflammatory response.

One specific mediator, bradykinin, relaxes the smooth muscle of the blood vessels, resulting in vasodilation; it also increases the permeability of vessels. Once the vessels have been dilated, blood flow increases into the area of heat concentration. 

If we think about blood circulation with the mindset of injury repair and healing, the increased permeability provided by bradykinin allows the leukocytes to come into the picture. Filtering themselves out of the vessels to clean up any tissue damage, they are just living the white blood cell dream.

There are three phases of the injury healing process: the inflammatory phase, the proliferation phase and the remodeling phase. One of them is contraindicated for heat.

The Red Light for Heat

In the inflammatory phase, for 72 hours, the tissues are damaged and the body is now actively containing the damaged tissue by protecting the area from further injury.

Cryotherapy is very helpful during this phase, to reduce swelling. Thermotherapy applied on a site of inflammation is a serious contraindication, whether it is after 72 hours of injury or not. This is when the green light turns red, friends. This is when we can get into trouble and kill some tissues. Let’s look at why.

It’s necessary to go into a brief explanation of hemodynamics here. Under normal circumstances, arterial blood flows into the capillaries. White blood cells, oxygen, nutrients and fluids permeate from the vessels to the tissues of that area. Then the venous blood flow carries away the used cells, fluids and cellular debris from the area.

Because veins have thinner walls, more elasticity and a wider diameter, venous volume compliance is higher than arterial volume compliance. This means veins can hold more blood within their walls, which can then become distended with excessive volume. Often this is called venous pooling.

All of this basically means that veins have a slower transit time of moving blood through venous circulation normally.

However, we aren’t talking about normal conditions. Placing a hot pack on a site of inflammation creates an enormous increase of arterial volume and pressure compounded upon what was already there.

Blood is moving to the site at a rapid rate. Venous volume, already slower to move out of the area, begins to back up. This ultimately causes hypoxia, or lack of oxygen in the area. The cells that received oxygen will metabolize it into carbon dioxide.

That carbon dioxide, cellular debris and various other waste products are now unable to permeate back into the vessels’ walls and can’t leave the site.

In this hypoxic state, lack of oxygen and increased waste products in the site will damage previously healthy tissue. Heat during the inflammatory phase can stop the healing process and also create double the damage. The result of that situation is called secondary hypoxic injury. 

So, say it with me: No heat during the inflammation phase. OK, good. 

The Green Light for Heat

The proliferation and restoration phases of healing both get the green light for heat applications. During the proliferation phase, scar tissue and brand-new tissues are being formed. Thermotherapy speeds up the oxygen uptake and quickens the healing process. The final remodeling phase is the process of restoring the structure and function of the injured tissues.

Even in cases of muscle splinting near the injury site, heat applications in conjunction with any other hands-on modality such as massage, stretching or neuromuscular therapy will decrease muscular tension and ultimately help improve proprioception. 

Wait! Can we use heat during a massage session to benefit the client’s neuromuscular system?

Of course.

Let’s go back to the vessels and that vasodilation. We discussed how the process begins once the heat is applied to the skin. The release of bradykinin causes vasodilation, but it also allows for increased vessel permeability. 

The permeability of the blood vessels allows interstitial fluid, the combination of water and various solutes, to seep out of the vessels along with the white blood cells. While the white blood cells are living their best life, cleaning up any damaged tissues in the area, the fresh interstitial fluid is replenishing the local cells’ cytoplasm while also delivering nutrients and electrolytes to those cells.

This increase in nutrients and fluid to the muscular tissue allows cells to heal and create more interstitial space between fibers. The combination of fluids and nutrients will create more muscular pliability and extensibility.

Applying heat to an area is a passive creation of thixotropy, or liquifying a viscous substance by creating heat through friction. When muscles are lacking that fluidity, they can become rigid and the muscle spindle cells become shortened. Thermotherapy can create muscular relaxation, increase flexibility, improve proprioception, and even lessen nerve sensitivity and pain.

In terms of pain, our bodies need to be a bit like Goldilocks. This hot pack is too hot, this hot pack is too cold. This hot pack is just right! When temperature is just right, in a nonpainful range, any pain occurring within the peripheral nerves can be inhibited. Thermotherapy is, after all, an analgesic, meaning that it lessens pain.

This pain inhibition is a two-part harmony, so to speak. First by the gate theory, that pain signals are weakened by non-noxious stimuli. Nonpainful heat would weaken the pain signal. The other part of this harmony goes back to circulation, and this time we are looking at neurotransmitters.

We have a neuropeptide called Substance P. Nociceptors are the nerve receptors for pain stimuli. Once Substance P binds with the nociceptors, the brain receives a pain signal as part of our defense mechanisms. Then, once thermotherapy is applied to the situation, heat-sensitive calcium channel blockers block Substance P at the nociceptor, so the pain signal is unable to make it to the brain.

Assuming that heat application is just the right temperature, the gate is blocked, Substance P is blocked and now the muscles can relax. That relaxation is now sustained by the autonomic nervous system, in a parasympathetic state of healing and reduced pain.

How Clients Benefit From Heat

Let’s bring it all together in a practical setting. You have a client with adhered muscles and during your session you apply a hot pack to the area for 20 minutes. During that 20 minutes the thermoreceptors signal the body to begin the inflammatory response.

This releases bradykinin, which increases permeability and dilates the blood vessels, therefore increasing the flow of blood.

That dilation and permeability allow for increased oxygen and nutrients to aid in healing and restoring any damaged tissues. The extra interstitial fluid creates more space between muscle fibers and replenishes hydration of the tissues. The combination of hydration and heat allows the muscles to become more pliable and less rigid. The pleasant comfort of heat blocks any pain signals to the brain.

If any pain stimulus is left, calcium channel blockers block Substance P and the muscles are relaxed and pliable. At this point, the conditions are right for such hands-on modalities as Swedish and deep tissue massage and trigger-point work to have the most impact of efficiency.

Thermotherapy has set the stage for massage therapy to be successful — and more importantly, for the client to feel relief.

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References

Gafiychuk, VV, Lubashevsky, IA, Datsko, BY. “Fast heat propagation in living tissue caused by branching artery network” (Nov. 18, 2005). Physical Review E.

Dehghan M, Farahbod F. “The efficacy of thermotherapy and cryotherapy on pain relief in patients with acute low back pain, a clinical trial study” (2014). Journal of Clinical and Diagnostic Research.

Kosaka, M, Sugahara, T, Schmidt, T, Simon, E. Thermotherapy for Neoplasia, Inflammation, and Pain (2001). Springer.


“Thermotherapy” (August 2019), Physiopedia (physiopedia.com). Retrieved Oct. 24, 2019.

“Pain Mechanisms” (June 2019), Physiopedia (physiopedia.com)Retrieved Oct. 24, 2019.

About the Author

Samantha Snair Yancey graduated from the massage program at Atlanta School of Massage in 2003. After returning to complete both esthetics and esthetics-instruction programs, Yancey began teaching in 2006. Her passion for learning brought her to her favorite topics: musculoskeletal anatomy and aromatherapy. Yancey is currently attending a clinical aromatherapy program while writing a curriculum for future continuing education classes. She wrote this article on behalf of the Atlanta School of Massage.

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