People swim for competitive sports, such as an Olympic event, as well as for aerobic exercise and recreation. As with other aerobic exercises, such as running, your body temperature, hydration levels and sweat rate are affected by your exercise intensity and the air temperature, but the water temperature you swim in can affect your swimming duration and performance. Learning how your body reacts to different water temperatures can help you avoid dangerous conditions when swimming.
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Taking a Dip in Cold Water
When you get into cold water, your blood vessels widen to allow warm blood to increase your body’s temperature. Your body will eventually start closing the blood vessels to maintain your core body temperature and prevent organs from shutting down. The body cannot restrict blood flow for long, so your blood vessels reopen, which increases the risk of cold blood flowing to your organs and leading to hypothermia. Anything below 60 degrees Fahrenheit without a wetsuit can lead to shivering or cold shock. The severity of symptoms depends on your tolerance to cold temperatures, according to the National Center for Cold Water Safety.
The Warm Water Effect
Swimming in water that is too warm -- over 90 degrees Fahrenheit -- can lead to overheating and exhaustion -- particularly when you are exerting yourself by swimming several laps or a marathon. Warm water increases your body temperature, which also raises your sweat rate and quickens dehydration. Your body tries to cool itself down through sweat to regulate your body temperature. Profuse sweating can lead to an imbalance of electrolytes, which can effect muscle mobility. Open-water swimming in warm climates can expose you to water temperatures that are too warm, which can cause muscle spasms and severe fatigue. USA Swimming notes that sometimes warmer water can be appropriate, such as for Aquatic Therapy, but activities like that are supervised and not done for very long.
Cold Water Versus Warm Water
Warm water at about 90 degrees Fahrenheit can increase your metabolism and speed when swimming, but a cooler temperature of 70 degrees Fahrenheit is safer for swimming because the body can adjust better to colder temperatures than warm water, according to a 1993 study published in the "The Journal of Sports Medicine and Physical Fitness." Swimming in cooler water also helps you swim for a longer duration without the risk of heat-related exhaustion. However, swimming in water cold enough to make you shiver can eventually lead to hypothermia. When swimming in warm temperatures, such as a heat wave in open waters, keep your exertion level low or swim for short durations to prevent heat exhaustion.
The Ideal Temperature
The water temperature ideal for swimming varies, depending on your activity. Generally, the more intense your aerobic activity, the lower the air temperature needs to be. USA Swimming states that water temperatures of 82 degrees Fahrenheit and cooler are ideal for competitive swimming and high-intensity swimming; the air temperature should be between 78 and 80 degrees Fahrenheit. For recreational swimming and moderate exercise, 86- to 88-degree water is optimal, while the air temperature should be between 82 and 84 degrees Fahrenheit. To avoid dangerous water or air temperature, swim when the pool is monitored by an aquatic fitness professional and ask about when the pool's temperature would be right for your activity.