At its November meeting of the Board of Directors, USA Triathlon (USAT) adopted new Recommendations for Multi-Sport Age Group Swim Segments. These new recommendations mark a step forward in terms of race safety. USAT also agreed to collect data during the 2014 season from every event regarding water temperature and athlete rescues, incidents of hypothermia or heat-related illness, and other medical emergencies that occur during the swim portion. These data will help to guide further review of the recommendations by the USAT Swim Collar Task Force and possibly set the stage for further scientific investigation about hypothermia and heat-related illness in the triathlete population specifically.

The graphic below illustrates the new recommendations:

These recommendations are targeted at race directors, local officials, and athletes. They apply to age group events but not to professional races. Satisfactory, or so-called neutral, water temperature ranges for races of various distances are defined as:

<750 meters, 55-89 F

750-1500 meters, 56-87 F

>1500 meters, 57-86 F.

The neutral temperature ranges are shown in green in the graphic. When the water temperature falls outside of the neutral range, the recommendations advise that the swim portion should be shortened or cancelled. These temperature ranges are shown in yellow or red in the graphic. Discretion is left to the race director, though, who may consider other safety-related factors such as air temperature, humidity, acclimation, regional adaptation, and wind.

There is no change to the current rules regarding measurement of the water temperature or to the use of wetsuits. From the USAT competitive rules:

Measuring Water Temperature. It is recommended, but not required that the water temperature for a race be finally determined by measurement made within 2 hours of the race start. A water temperature measurement should also be taken prior to any pre-race meetings in order to forecast to the athletes as early as possible the likely water temperature on race day and the likelihood of whether wet suits will be allowed on race day. Wet suits. Each age group participant shall be permitted to wear a wet suit without penalty in any event sanctioned by USA Triathlon up to and including a water temperature of 78 degrees Fahrenheit. When the water temperature is greater than 78 degrees, but less than 84 degrees Fahrenheit, age group participants may wear a wet suit at their own discretion, provided however that participants who wear a wet suit within this temperature range shall not be eligible for prizes or awards. Age group participants shall not wear wet suits in water temperatures equal to or greater than 84 degrees Fahrenheit.

Open Water Swimming, Hypothermia, and Heat-related Illness

Open water swimming is as old as the ages. Mass participation in open water swimming events is relatively new, though.

In today’s triathlons and open water swimming events, there is tremendous heterogeneity among the participants in terms of age, size, body fat, and swimming ability. All of these factors affect an individual athlete’s ability to withstand prolonged exposure to cold or warm water temperatures. The important concept is maintenance of core body temperature. In ordinary circumstances, the human body core temperature is tightly controlled to reamin near 37 C by processes known as thermoregulation. There is a balance between heat gained from the environment or generated by exercise….and the heat lost to the environment.

The condition of hypothermia is loosely defined as a core body temperature <35 C. With mild hypothermia, there may be an increase in the blood glucose level and increases in both the heart rate and respiratory rate. With a continued fall in core body temperature, shivering begins, muscle movements become labored and then difficult, and mental confusion develops. This progression can be insidious. Athletes should be vigilant. With severe hypothermia, the heart rate and respiratory rates fall, there is a further decline in mental status, and individuals may die of cardiac arrest.

During cold exposure, the body can generate heat through shivering and conserve heat by vasoconstriction of the peripheral blood vessels. For an athlete, exercise is also a mechanism to generate body heat. Because of differences in their intrinsic physiology or differences in body fat, children and older adults will chill faster than young and middle-aged adults. As a group, men will chill faster than women. For an adult who is not swimming, the neutral water temperature that will allow maintenance of a stable core body temperature is approximately 32-34 C. For adults who are swimming (at a moderate pace, for up to 60 minutes) the neutral water temperature is approximately 21-25 C (70-77 F). For harder or shorter efforts, the neutral temperature may be substantially lower. Swimmers will become hypothermic at a rate which is proportional to the duration of immersion and the difference between the neutral temperature and the ambient water temperature.

Once the core body temperature falls during cold water immersion, it may continue to fall even after removal from the water, in a condition known as afterdrop. In a classic study of non-wetsuit swimmers in San Francisco Bay, 5 of 11 swimmers developed hypothermia after a swim of up to 45 minutes in 53 F water on New Year’s Day. In 10 of the 11 swimmers, there was a significant decrease in the core body temperature after emerging from the water, over a period of of up to 30 minutes. After a long, cold swim, athletes should exercise special caution during the 1st transition and the beginning of the bike portion.

The possibility of hypothermia during open water swimming is what prompted the use of wetsuits for triathlon events. By adding insulation and allowing the body to conserve heat, the wetsuit effectively lowers the neutral water temperature for any given open water swim. Each of the various governing bodies has developed policies about water temperature and the use of wetsuits.

At the other end of the temperature spectrum, hyperthermia results when the core body temperature is elevated. In medical circles, we use the term fever to characterize a mild to moderate rise in the core temperature. While there’s no official definition, we might choose >38 C to indicate a fever. With hyprethermia due to heat exposure, the body’s temperature can continue to rise to >40 F and heat stroke can result. Symptoms include an increase in the heart rate and respiratory rate, muscle weakness or cramping, and eventually a deterioration in the level of consciousness. The human body responds to hyperthermia by sweating and by dilating the peripheral blood vessels and allowing heat to transfer more easily to the environment. It is easier for the body to transfer heat to surrounding air than to surrounding water.

For adult men who are immersed but not swimming, the core body temperature has been shown to increase during prolonged exposure to water temperatures of 36-37 C. For adults who are swimming at moderate intensity, the core body temperature may increase in water temperatures of 28-32 C (82-89 F). These facts are the basis for having an upper limit of water temperature for which wetsuit use is allowed and safe.

Water Temperature Guidelines for Other Organizations

The issue of safe temperatures for open water swimming events has long been controversial. The several governing bodies for open water swimming have each studied this issue and developed their own guidelines in recent years.

USA Swimming, the national governing body for swimming in the United States in 2011 developed a comprehensive list of safety recommendations following the death of American open water swimmer, Fran Crippen, during a race held in the United Arab Emirates in very warm water. Included were changes to USA Swimming’s water temperature guidelines. Citing from the USA Swimming rules for open water swimming (2013 Rulebook):

The water temperature shall not be less than 16 C (60.8 F).

For races of 5K and above, the water temperature shall note exceed 29.45 C (85 F)

The air temperature and water temperature when added together shall not be less than 30 C (118 F) nor greater than 63 C (177.4 F).

FINA, the international governing body for the aquatic sports (swimming, diving, synchronized swimming, water polo, and open water swimming) sets the minimum allowable water temperature for open water swimming at 16 C (60.8 F) (see FINA 2013 Open Water Swimming Rules). In June of this year, FINA adopted a new rule governing the maximum temperature allowable for open water swimming events. At the recommendation of its Technical Open Water Swimming Committee, FINA has now set the maximum allowable temperature at 31 C (87.8 F). This new rule came under almost immediate criticism because it is less restrictive than the current USA Swimming limit of 85 F.

For additional context, FINA specifies the allowable water temperature for swimming pool events to be between 25 and 28 C, and recognizes that athletic performance falls off at water temperatures greater than 27 C.

The International Triathlon Union (ITU), the international governing body for the sport of triathlon, has adopted water temperature safety guidelines that also account for the race distance and the air temperature. All swims should be cancelled for water temperatures <13 C and all long distance swims (3000m or 4000m) should be cancelled for water temperatures <14 C. Races can be shortened depending upon the air and water temperatures (see the 2013 ITU Competition Rules). For age group athletes, the use of a wetsuit is forbidden above 22-24 C and is mandatory below 14-16 C, depending upon the race distance.

World Triathlon Corporation (WTC), the owner of the Ironman brand events, announced their SwimSmart initiative in May of this year. For their North American Ironman events, WTC adopted a safe temperature range of 52 to 88 F. If the water temperature is outside that range, the swim portion of the event will be shortened or cancelled. For all of their events, wetsuits are permitted for water temperatures up to 76.1 F (24.5 C) and prohibited for water temperatures greater than 83.8 F (28.8 C). Athletes wearing a wetsuit when the water temperature is between those cutoff temperatures are not eligible for age group awards.

My Advice

For Athletes. Athletes are usually aware of the rules regarding wetsuit use. They should also be aware of the potential issues of hypothermia or heat-related illness during a race. These new recommendations from USAT provide a framework for critical thinking about this issue. Athletes should use sound judgment and extra caution when participating in events at the extremes of the temperature range. At the low end, extra consideration should be given to the use of a wetsuit even if a race is short. USAT chose not to implement a policy about mandatory wetsuit use, but they do allow race directors to enforce such a rule. My personal view is that swimmers should use a wetsuit for any race where the water temperature is 60 F or less. At the high end of the temperature range, athletes should pay extra attention to their hydration and make certain that their pace or effort is moderated. In the end, only the athlete can make the decision to participate. Water temperature is one factor that should be taken into consideration when athletes make judgments about their safety. If you think it’s unsafe, don’t participate.

For Race Directors. The new recommendations define a very broad neutral temperature range. The vast majority of events will be held in venues where the water temperature will fall into this range. When the water temperature falls outside the neutral range, though, race directors should be very cautious about deviating from the recommendations to shorten or cancel the swim portion of a race. In cold conditions, race directors should give due consideration to requiring athletes to wear a wetsuit. For races at either extreme of the temperature spectrum, race directors should provide athletes with information about hypothermia, heat-related illness, and advice about the use of a wetsuit.