I was asked this question by someone that attended one of my talks recently and I thought I'd share my answer here for everyone to benefit from.
A cold plunge is not exactly like a bout of intense exercise, but it can be a similar type of stressor that triggers some of the same physiological responses in the body.
The human body is a complex machine, and the nervous system plays a crucial role in regulating its functions. The nervous system is divided into two parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The PNS is further divided into the sympathetic and parasympathetic nervous systems, both of which work together to maintain homeostasis (balance) in the body.
The sympathetic nervous system (SNS) is responsible for the "fight or flight" response that prepares the body to deal with stressors such as danger or physical exertion. It increases heart rate, dilates air passages, and diverts blood flow to the muscles, preparing the body for action. The SNS is activated by the release of adrenaline and noradrenaline from the adrenal glands.
On the other hand, the parasympathetic nervous system (PNS) is responsible for the "breed and feed" response. It slows down heart rate, constricts air passages, and increases blood flow to the digestive system, promoting relaxation and recovery. The PNS is activated by the release of acetylcholine.
During exercise, the body responds by increasing heart rate and blood pressure, increasing blood flow to the muscles, and increasing the production of hormones such as adrenaline and noradrenaline. These responses are intended to help the body cope with the increased demand for energy and oxygen during physical activity.
Similarly, when the body is exposed to cold water, it responds by increasing heart rate and blood pressure, constricting blood vessels, and shunting blood flow to the core to maintain body temperature. These responses are intended to help the body cope with the cold stress and protect vital organs.
However, while exercise is a form of physical activity that requires energy expenditure and involves muscular contractions, a cold plunge is a passive stressor that does not require any physical exertion. Additionally, the effects of a cold plunge may not be as long-lasting as the effects of exercise, which can lead to more sustained improvements in cardiovascular health, muscle strength, and other aspects of physical fitness.
That being said, a cold plunge can be a valuable addition to a well-rounded fitness and recovery routine, as it can help to reduce inflammation, improve immune function, promote relaxation, and can help to reduce stress and anxiety.
In conclusion, the sympathetic and parasympathetic nervous systems play crucial roles in regulating the body's responses to stressors such as exercise and cold water exposure. Understanding how these systems work can help you to optimise your training and recovery protocols, while also reducing the risk of injury or other negative effects. Just like with exercise, it is important to approach cold water exposure safely and gradually and to seek professional advice if you have any underlying health conditions or concerns.