There are three potentially hazardous physiological responses associated with going into cold water. The first is the cold shock response (CSR), which is the uncontrollable gasping, breathing, and increase in heart rate that occurs for about 90 seconds when you first go in. The second is cooling of the nerves and muscles close to the surface of the body, particularly in the arms and legs that, when cooled enough, incapacitate you and stop you exercising . The third is hypothermia as deep body temperature falls below 35°C, this normally takes at least 30 minutes to happen in an adult in cold water.
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