Understanding the Science behind Hot and Cold Therapy
Hot and cold therapy has been used throughout the sporting world as a widely recognised tool for managing muscle soreness, inflammation and overall recovery post exercise and sport activity. Hot and cold therapy utilize the body’s natural response of thermoregulation (the ability to maintain a constant body temperature) by creating a vascular response to improve overall healing and promote optimal muscle conditions and ultimately function.
Hot and cold therapy seems like such a simple concept, however, their effectiveness stems from complex physiological functions that harness the power of the body’s response to outside temperature changes is how the process works. Although used widely across the sporting population, the science behind how it works is not vastly understood. The purpose of this blog is to help athletes, practitioners and patients understand the science behind the therapy in order to understand and unlock the potential for maximizing recovery and ultimately improving performance in sport and everyday life.
Hot Therapy (Thermotherapy)
As the name states, hot therapy or thermotherapy is the process of applying heat to affected areas in various modalities such as full body immersion, heat pads, warm compresses or more recently with technology such as infrared sauna. The process and physiological steps are the same for all of the thermotherapy modalities; Vasodilation.
Vasodilation translates to the dilation of blood vessels within the body. When blood vessels dilate, this means that they open and allow for greater blood flow throughout the body including but not limited to muscles around the body. Increases in muscle blood flow aid in the recovery from intense, muscle-damaging exercise through several different possible mechanisms:
First, the delivery of substrates in the blood such as glucose and essential amino acids that are required for refueling and tissue rebuilding is enhanced which ultimately will lead to an increased rate of tissue healing.
Second, the removal of by-products of exercise such as hydrogen ions (responsible for soreness in muscles post exercise) as well as other substances that can cause a delayed healing response is targeted and removed at a faster rate due to the increase of blood flow to the affected areas. (Kim, Monroe, Gavin, & Roseguini, 2020)
Thermotherapy also helps with the feeling of tightness throughout the body which is usually felt post exercise. This occurs when the muscle fibers shorten and stay in a shortened position post exercise. Heat therapy activates receptors within the brain (TRPV1) receptors which help to regulate pathways through the nervous system which affect muscle tonicity (tightness) and relax muscles. (Malanga, Yan, & Stark, 2014) Heat also helps to cause an increase in elasticity of connective tissue called fascia, which ultimately will help to reduce spasms, stiffness, musculoskeletal pain and increase muscle flexibility.
Cold Therapy (Cryotherapy)
Unlike Thermotherapy, Cold therapy or Cryotherapy is application of something cold, whether that is submersion in cold water, application of ice or an ice pack to a certain area, use of a game ready machine or whole body ice therapy in an ice bath.
The primary mechanism that occurs when cryotherapy is applied to the body is called Vasoconstriction or the narrowing of the blood vessels within the body. Cold causes the blood vessels to constrict, restricting blood flow to the region. This can help alleviate swelling and inflammation which are often common after exercise and activity which causes micro damage to the muscle tissue.
When we move and when we exercise we are breaking down stored energy in the muscle. As a result of this process, the body produces by products, think of it like the exhaust of your car when you drive. The natural process of elimination of these by-products is via 2 mechanisms, it is transported via blood flow and recirculated around the body or it is used again in the muscle as a source of energy. However, this process doesn’t always go smoothly and often these by-products are left behind in the muscles and get stuck. This combined with the microtrauma that occurs with exercise creates a feeling of soreness.
This is when we feel delayed onset of muscle soreness or DOMS (delayed onset muscle soreness). The soreness we feel after exercise. The combination of microtrauma as well as pooling of blood in the vessels creates a feeling of soreness and stiffness post exercise.
Vasoconstriction helps with constricting the blood vessels within the muscle, this mechanism helps to squeeze any pooling blood that is left over or stuck within the muscle and flushes it out of the affected tissue.
Cold temperatures also reduce blood flow to the affected area via vasoconstriction. This has been thought to reduce swelling and tissue breakdown after an injury or after procedures such as surgery.
An increasingly more popular form of recovery post exercise is known as combination therapy, combining the use of thermotherapy and cryotherapy together in contrast with each other. This method of therapy utilizes the two modalities we mentioned earlier, vasoconstriction and vasodilation. Alternating between these two methods of recovery induces a pumping effect within the vascular system.
Ultimately this pumping effect helps to both squeeze left over waste products of exercise and then allow for an influx of fresh blood flow to the muscles which results in increased oxygen, increased essential amino acids and removal of waste products and swelling which will overall improve lower limb function, reduce soreness within the muscles and promote a quicker recovery. (Shadgan, Pakravan, Hoens, & Reid, 2018).
By repeating these two methods within a 20-30 minute session the constant changing of temperature and vascular size has been shown to improve recovery and reduce the overall DOMS felt post exercise which can get an athlete ready for performance quicker, reduce overall fatigue and therefore injury risk and allow for harder training at their next session.
Kim, K., Monroe, J. C., Gavin, T. P., & Roseguini, B. T. (2020). Local heat therapy to accelerate recovery after exercise-induced muscle damage. Exercise and Sport Sciences Reviews, 48(4), 163–169. doi:10.1249/jes.0000000000000230
Malanga, G. A., Yan, N., & Stark, J. (2014). Mechanisms and efficacy of heat and cold therapies for Musculoskeletal injury. Postgraduate Medicine, 127(1), 57–65. doi:10.1080/00325481.2015.992719
Shadgan, B., Pakravan, A. H., Hoens, A., & Reid, W. D. (2018). Contrast baths, intramuscular hemodynamics, and oxygenation as monitored by near-infrared spectroscopy. Journal of Athletic Training, 53(8), 782–787. doi:10.4085/1062-6050-127-17