The reason why many navy seals and athletes take cold showers as part of their training regiment is because of the strengthening effect that it has on the nervous, immune and circulatory systems. A key phenomenon that takes place is that it increases the trainees physical and mental ability to remain calm under a stressfull circumstance. If one is able to override the impulses of their amygdala (from the limbic system) with logic (from the prefrontal cortex), they will strengthen their prefrontal cortex. Repeatedly using logical processes to calm your body--such as taking deep breaths, verbal reassurance, meditation, visualization techniques--builds the ability to harness the body's fight or flight response.
Habitual cold showers also strengthen the body's immune system by boosting the production of white blood cells (leukocytes) that fight off foreign bodies. Additionally, exposure to cold temperatures results in vasoconstrictions of blood vessels. This means that blood is restricted to the extremities, but pools around the central organs. This allows the blood to be easily oxygenated and pumped full of nutrients. When the blood returns to the rest of the body body's tissue it restores an oxygenated and nutrient rich supply. This "reset" of the blood supply helps to cleanse the body of any lingering inflammation--the main culprit that compromises the immune system!
Exposure to cold temperatures can increased overall longevity by enhancing the production of two key enzymes in cellular metabolism, AMPK (adenosine monophosphate-activated protein kinase) and mTOR (mammalian target of rapamycin). Both of these enzymes help to convert white fat into brown fat. To clarify, white fat is adipose tissue that stores excess energy, where as brown fat burns more quickly by breaking down glucose for regulating body temperature. Excessive storage of white fat leads to obesity, cardiovascular disease, and various other inflammatory pathologies. Therefore, the result of this enhanced cellular metabolism is weight loss, warding off disease, and thus increased longevity.
When submerged in cold water, the amygdala--which regulates emotions such as fear or aggression--sends a distress signal to the hypothalamus. The hypothalamus injects hormones throughout the body...
Adrenaline (epinephrin) and noradrenaline (norepinephrine) are secreted from the adrenal glands to induce the body's fight or flight response (sympathetic response). These hormones pump the circulatory system into hyper drive--heart rate escalates, blood volume increases, and pressure on blood vessel's walls strengthen. This is why cold showers are like a workout for the circulatory organs and will strengthen them over time. These hormones also vasoconstrict certain vessels to redirect blood to organs that are necessary for survival--like the extremities for enhanced strength and the brain for enhanced cognition, rather than the currently irrelevant reproductive and digestive organs. The trachea is dilated to inhale more oxygen than normal. Fat is broken down to access the energy reserves stored inside and blood sugar levels increase to provide the body with excess energy. This is why post-cold shower people feel alert, focused and energized!
Dopamine is the third hormone in the catecholamine family--working with adrenaline and noradrenaline to regulate the autonomic nervous system in a stress response. This neurotransmitter regulates motor control, emotional response, and thought processes in trauma. It holds a critical role in producing a feeling of well being that calms the body after the traumatic event has ceased. Dopamine fires from the reward center of the brain, thus increasing one's desire to repeat an activity over again. This is why after a cold shower one may feel an overwhelming feeling of peace, along with a desire to experience the rush of a cold shower again.
Endorphins are hormones signaled by adrenaline in order to counteract the stress response of the catecholamine hormones. They act as an antidepressant and natural pain killer. This is why post-run, runners often experience an increased positive outlook on life and also do not initially feel the aching of their muscles. Similarly, people who incorporate cold showers into their routine experience feelings of elation, euphoria and possibly a decrease in pain signals to the brain.
To recap, cold showers train one's mind to remain calm under stress, increase longevity, produce a feeling of wellbeing, and strengthen the circulatory, immune and nervous systems. To receive the optimal benefits end your shower with water as cold as 50 to 60 degrees Fahrenheit. Start out with 2 cold showers a week for 30 seconds each, and work your way up to 4 showers a week for 5 minutes each. It is possible for you to harness the endurance and resilience of a navy seal and achieve the vitality of an athlete...one cold shower at a time!
*DISCLAIMER: If you suffer from any cardiovascular or circulatory pathologies, please be advised to seek a health professional before participating in cold showers as the exposure will alter blood pressure, vasoconstriction and circulation to extremities, and may be a contraindication for you!