When submerging into cold water, several responses take place within your body. Learning how to handle to the cold and knowing your limitations is key to staying safe during open water swimming.
The initial cold-shock response
The cold-shock response lasts for only a minute or two after entering cold water, and refers to the effect of the cold on your breathing.
Initially, there is an automatic gasp reflex in response to rapid skin cooling, and breathing rate also tends to increase. The cold-shock response can be controlled by remaining calm and controlling your breathing.
How your body copes with the cold
Your body is built to maintain a stable core temperature between 36.5 - 37.5°C, a process known as thermoregulation. This is primarily controlled by an area in the brain called the hypothalamus, which initiates a variety of responses to temperature fluctuations.
When the body is too cool, body heat is preserved. Vasoconstriction narrows blood vessels to decrease blood flow to the extremities (hands and feet), hereby decreasing heat loss to vital organs such as the heart and lungs. You may feel your fingers and toes starting to get cold or even slightly numb.
If exposed to the cold for too long, the body loses it's ability to maintain a stable core temperate, and gradually starts to lose body heat. However, even in ice water (~0°C), the cold can be sustained for about an hour before hypothermia sets in, so don’t panic! Your body also adapts to frequently being exposed to the cold, and it gets easier to handle every time you get in.
Water entry tips:
Slow emersion. Enter the water slowly so that your body can adapt to the change in temperature. It is not advised to dive into very cold water, especially if you are not experienced in cold water swimming.
Control your breathing. As you enter cold water, focus on slowing and controlling your breathing, especially when submerging your face. Remember that the cold-shock response will only last a few minutes before your body settles into the cold.
Remain calm and relaxed. As you start swimming, remain calm and relaxed. Focus on lengthening your stroke and relaxing your muscles. Start off swimming at an easy pace, and once you feel comfortable, you can start increasing your pace.