Performance and Recovery
Possibly the most well-documented use of WBC in the U.S. is for the recovery and performance of athletes, centering around post-workout inflammation and its role in muscle damage and fatigue. For a more detailed explanation of the general inflammation process, please see the "Inflammation" section lower on this page.
In a workout, training session, event, or any other strong physical exertion, you are asking ("forcing" is maybe more honest) your muscles to work harder and create more energy than usual which is a stress on the body. The response of the body to this stress is to make pro-inflammatory agents, namely the cytokines interleukin-1 beta (IL-1b) and tumor necrosis factor-alpha (TNF-a). When kept at a reasonable level, the muscle tissue welcomes the arrival of these agents. They can help in the recovery process. However, with the level of exertion that is common for an athlete, a long distance runner, a dancer, etc., the muscles are flooded with these pro-inflammatory molecules at a level that is often higher than necessary for the recovery process. In this event, rather than aiding in the recovery process, they actually act to further damage the muscle tissue. This is commonly referred to as "overtraining". Exposure to WBC triggers the release of anti-inflammatory agents, which help to mitigate this damage.
To get the greatest benefit, WBC should be scheduled as close as possible to the end of your workout, as this is the time of the greatest pro-inflammatory cytokine production. It has also been shown that WBC sessions before a workout or athletic event can enhance performance. This is likely because the production of pro-inflammatory agents are delayed or the ratio of anti- to pro-inflammatory agents is tipped in favor of the anti-inflammatory agents for a longer period, thus delaying muscle fatigue. In a recent study, kayakers using WBC leading up to an event performed statistically better.
However, it should be understood that the benefits of WBC or any cold-shock therapy in relation to athletic performance should only apply to individuals training a level where the body's auto-inflammatory response becomes excessive. This includes those in professional, collegiate, and potentially high school athletics, cross-fit, MMA, long-distance running, dancing, etc.
It should also be noted that weight-lifters and those looking to gain muscle mass would likely not benefit from WBC, as these pro-inflammatory agents typically aid in the building of that desired level of muscle mass.
To understand the effect of WBC on pain, it is first necessary to understand the pathways along which pain is perceived. Pain stimuli travels from the point of stimulus, whether it be from the body's periphery, muscles, joints, or organs, through the spinal cord to the brain through a process of nociception. In nociception, afferent signals originate at free nerve endings and travel along nerve fibers in the peripheral nervous system (in the case of pain, mostly along C nerve fibers or A-delta nerve fibers) to the spinal cord. At this point, they release transmitters (glutamate, substance P, etc.) which are received by receptors on the spinal cord (the posterior grey column). The pain signal is transmitted along the spinal cord to nearby segments, the thalamus, and ultimately to the cerebral cortex, where it is perceived as pain. In an effort to counteract this pain, the brain releases endorphins and serotonin locally and gamma-aminobutyric acid (GABA) in the central nervous system. While these mechanisms often reduce the pain intensity to a certain level of toleration, they are limited in their effectiveness.
In the case of chronic pain (pain that lasts for more than six months), this repeated release of signal transmitters at the end of the peripheral nerve fibers leads to what can be called a pain wind-up. The receptors in the posterior grey column become hyper-sensitized and their electrical responses leads to an inappropriate amplification of pain perceptions, i.e.- a stimulus that should elicit a minor pain perception instead is perceived as a major pain.
With exposure to WBC, thermo-sensors (in this case cold sensors) which travel along the A-delta nerve fibers, flood these pathways, traveling at a faster rate than pain afferents traveling along the same route. This, along with the increased release of endorphins, as well as the neurotransmitter and hormone norepinephrine, can possibly aid in the reduction of pain perception. This inhibition effect lasts for several hours after the exposure. Repeated exposures (several WBC sessions in a series) seem to prolong this effect in relation to chronic pain. While this prolonged effect is still anecdotal, a level of relief of chronic pain lasting several months after a strong initial series of WBC has been often documented. It has been postulated that cold stimulus has a counter-irritation effect which over time lessens this pain wind-up and sensitization at the confluence of the nerve fibers and spinal cord. However, further study is needed to explain this long-lasting effect confidently, and even clinically prove its existence, and it is advisable not to rely exclusively on WBC, but to use it in tandem with other forms of active physical therapy and even psychological therapies.
When working appropriately, inflammation is a welcome soldier of the immune system which aids in the repair of damaged tissue. When such damage occurs, mediators trigger the release of pro-inflammatory agents (histamine, bradykinin, substance P,...etc.) Swelling and pain associated with these agents lead to the impairment of the affected region, quelling its use and allowing it time to repair. This is known as normal acute inflammation.
However, the components of inflammation that are capable of destroying microbes (T-cells, IL-1 a & b, TNF-a, etc.) can also damage normal tissue when acting inappropriately or over-zealously. The two negative types of inflammation are acute over-inflammation and auto-immune disorders which lead to chronic and unnecessary inflammation. While acute over-inflammation was dealt with in the "Performance and Recovery" section above, the known mechanisms in the reduction of inflammation are the same with the chronic inflammation associated with autoimmune disorders. The cold shock stimulus increases norepinephrine release, anti-inflammatory cytokine release, and can suppress the release of pro-inflammatory cytokines. In addition, WBC induces the process of vasoconstriction, the tightening of the muscles around the veins in the body's periphery. This is in an effort to conserve heat, pulling the blood from the less vital extremities to the body's core, where it can circulate around the vital organs and lessen heat loss through convection. This tightening of the veins restricts the pathways of pro-inflammatory agents to muscles and joints.
One of the most common benefits reported with WBC is better sleep. While the cause of this is still open for debate and requires further research, there are a few theories that hold water. The first is through a lowering of cortisol levels in the body. Cortisol is a hormone which regulates 20% of our genome, including parts of the circadian rhythm (the wake/sleep cycle). Chronic stress increases cortisol levels which leads to a deregulation of these functions. Studies have shown that WBC is associated with a decrease in cortisol levels, as well as an increase in the testosterone-to-cortisol ratio.
Other theories postulate a connection between the response of the autonomic nervous system and it's role in maintaining homeostasis and proper central activity levels within the organism. While a further theory suggests an action within the reticular formation, the interconnected portions of the brain responsible for consciousness and how we perceive the world around us. Though it could just be something as simple as the aftermath of an endorphin rush.
Mood Enhancement / Depression & Anxiety
WBC and other cold shock therapies have long been associated with an elevation of mood. In recent years, it has been studied as a supplemental treatment for depression and anxiety. This can partially be explained by the release of endorphins by the brain as a response to the cold shock. A further explanation which is being studied is associated with the release of norepinephrine. Norepinephrine (also called noradrenaline) is released both in the brain and in the body. In the body it acts as a hormone, causing vasoconstriction, the activation of anti-inflammatory agents, and an analgesic effect (pain relief). In the brain, norepinephrine acts as a neurotransmitter and is associated with focus and attention, the ability to contextualize new information, energy elevation, and mood enhancement. Norepinephrine re-uptake inhibitors (Wellbutrin, Zyban) are a common pharmacological treatment for depression and anxiety. Studies have shown that WBC is associated with an increased level of norepinephrine (a 2- to 3-fold increase), a reaction which remains consistent after multiple exposures (i.e.- the body doesn't reach a level of acclimation and release less norepinephrine on the 15th exposure than it did on the 1st.) The positive difference between the use of WBC as opposed to a norepinephrine re-uptake inhibitor is there are no pharmacological alterations (chemical side effects).
As a response to WBC, the body triggers a temporary increase in metabolism through a process called thermogenisis (how your body produces its own heat). Thermogenisis manifests itself in the body in two ways: shivering and non-shivering. Shivering is the spastic muscle twitching that we have all experienced (and some individuals will experience during WBC). Non-shivering thermogenisis is achieved through the release of energy. At the cellular level in brown fat, a protein called uncoupling protein-1 (UP-1), also known simply as thermogenin, acts upon the cells mitochondria and allows energy to be dissipated as heat.
While this increase in metabolism will burn calories, it would be unreasonable to expect WBC to be a cure-all in weight loss goals. It could however be used as part of a weight loss routine including a healthy diet and exercise.