Cold Water Swimming: What Does the (Limited) Research Say?


One of my ‘old’ school buddies now lives in London. A few months ago he asked me to write a paper on open water swimming in the cold. So Rod here it is. There is very little research in this area. In this article I’ve tried to distil the important applied research findings and what they mean for open water swimmers who swim in the cold.

FINA’s Open Water Swim rules tell us that the lower limit for water temperature (measured 1 m below the surface) is 16 degrees C (60.8 F). If water temperature is lower, the event should be cancelled. This figure of 16 degree C is based on the fact that both male and female swimmers will not experience dangerous declines in body temperature in water temperatures of 16 degrees C or higher when swimming at typical open water race speeds.

In triathlon, British Triathlon has the following guidelines:

  • The minimum water temperature at which wetsuits are optional is 14 degrees C
  • At temperatures less than 11 degrees C, no swim takes place
  • At the following water temperatures the maximum swim distances are mandatory: 13 degrees C – 200om; 12 degrees C – 1000m; 11 degrees C – 500m

The classic cold and open water swim, the English Channel, is typically just below the FINA recommended 16 degree C figure during the open season with many other open water swims and triathlons often held in cold water with wind and waves and ocean currents also contributing to body heat loss. Moreover, the longer the swim, generally the slower the pace meaning that you are not generating enough body heat to offset the heat loss into the water. Thus, in longer, colder events, we may be at risk of hypothermia where the body temperature drops below 35 degrees C (normal is 35.5-37.5 degrees C or 97.7 -99.5 degrees F), especially if not acclimatised to the cold water.

The Four Stages of Cold Water Immersion

The limited research available suggest four stages of physiological responses to cold water immersion.

  1. Initial Immersion (First 2-3 minutes) We all know that feeling of walking into or jumping into cold water. We uncontrollably gasp for air, hyperventilate, our heart races, and our stress hormone levels adrenaline and cortisol elevate! This response is a reflex we all have. This response peaks in the first 30 seconds of immersion and adapts over the first 2 minutes of immersion. Research has shown that the cold water hitting our skin, the reflex shortness and gasping for breath and possible face immersion if swimming all combine in a nervous system overload that can have a major impact on our heart, particularly in older swimmers with possible cardiac issues. This ‘cold (water) shock’ of cardiac strain and gasping for breaths peaks in water between 10-15 degrees C and is the reason why 60% of cold water deaths occur in the first minute or so of exposure to cold water. Even in triathlon, the USA Triathlon Fatality Incidents Study reported 79% of deaths in US triathlons between 2003 and 2011 occurred during the swim with unexplained sudden cardiac death rather than hypothermia the most likely cause of death. Gradually entering the cold water is one solution to this issue. Allow the body gradually gets used to the cold. Breath holding is NOT recommended NOR is quick immersion as both these have been shown to dramatically increase heart issues in cold water.  Another solution is to ensure either a wetsuit (and hood) or lanolin/grease is used to insulate our body from the cold water hitting our skin and overloading the nervous system.
  2. Short-Term Immersion (3-30 minutes) The major problem during this period is neuromuscular cooling. That is, both the nervous system and muscular system are affected by the cold that has worked its way through the skin and affecting both the muscle’s ability to generate energy and the nervous system’s ability to deliver the stimulus for muscles to contract effectively. Watch the video of an Olympic breaststroker in a cold water experiment to see this in action. Lower muscle temperatures lower the muscles ability to generate energy and heat and thus contract, and thus strength and power decrease leading to slower performances. Over time, blood flow to these muscles drops as the muscle blood vessels constrict. This leads to a drop in oxygen delivery and less ability to remove lactic acid, both of which impact on muscle performance. Indeed, research has shown that maximum aerobic capacity falls in relation to drops in both muscle and deep body temperature with 0.5 degree C drop in body temperature leading to a 10-30% fall in both aerobic capacity and blood flow out of the heart.  The arms are most susceptible to these earlier stated affects because they have a high surface area to mass ratio meaning they lose heat quickly but can’t generate heat because of the relatively low muscle mass. This fact is a strong argument for full-length wet suits in open water swims that allow wetsuits. Lathering up with grease/lanolin under the arms and over the arms also makes sense.
  3. Long-Term Immersion (30 minutes plus) Even in ice-cold water, research suggests serious hypothermia does not arise for at least 30 minutes in adults. Once it hits, hypothermia affects our ability to generate energy and heat, lowers blood flow to skin, the brain and muscles and affects nervous system function. Progressively, the signs and symptoms of hypothermia are shivering (at 36 degree C body temperature), confusion, disorientation and introversion (35 degree C), amnesia (34 degree C), cardiac arrhythmias (33 degree C), clouding of consciousness (30-33 degree C), loss of consciousness (30 degree C), ventricular fibrillation (28 degree C) and death (25 degree C). Be wary of these signs and ensure your support team are too.
  4. Finishing and Leaving Water During cold water rescue, research has shown that about 17% of deaths occur just before, during or just after rescue. Research suggests the stress hormones (adrenaline, cortisol reduce and slow metabolism. In cold water, there is also a significant reduction in blood volume due to water pressure and cold-induced blood vessel constriction causing diuresis (increased urination) when immersed in cold water. There may also be a dramatic drop in arterial blood pressure when going from horizontal to vertical. So warm down slowly and gradually move into the vertical position rather than jumping up to vertical after swimming.

Can We Acclimatise to Cold Water?

Insulative cold acclimation has been shown to occur when people are repeatedly exposed to a cold stimulus such as cold water where the body temperature is dropped repeatedly. Such exposure causes physiological and perceptual changes that lead to heat retention, reduction in shivering, and improved heat sensation. These changes lead to warmer and less fatigued muscles, greater levels of body insulation and better maintained deep body temperature. This in turn has been shown to lead to cold acclimatized athletes consuming 20-30% less oxygen than their acclimatised peers during exercise.

Both aerobic fitness levels and body fat levels are important for cold water swimmers. The fitter one is the more energy and heat can be generated. The more body fat a swimmer has in the cold, the better the ability to be insulated against the cold water. However, previous research has shown that cold water swimmers can be thin provided they are fast, they can be fat and fast, and they can be fat and slow, but they cannot be thin and slow.

Previous research strongly suggests deliberate training behaviours prepare both the mind and body for cold water swims. These behaviours include:

  1. Systematic and gradual exposure to cold water – gradually decreasing the temperature and amount of time you expose yourself to that cold water.
  2. Progressive increases in swim mileage
  3. Practicing pain management, feeding, urinating and vomiting!!!
  4. Train in open water with currents and waves and chop if that is what the goal swim is to be like.

 The Mental Side

Open water swimming in cold conditions such as the English Channel is not only a physical challenge, but a battle of the mind over matter. A great research study by Hollander and Acevedo (2000) identified the key psychological characteristics of successful channel swimmers after interviewing them within 2 months of completing the swim.  After analysing the key themes from the interviews, the researchers summarised the swimmers suggestions when it came to successfully completing the English Channel:

  1. Train to approximate the conditions. That is, train in cold water, practice feeding in rough conditions, be ready to encounter sea life, nausea, vomiting and urination problems.
  2. Develop a strong mind set so that no matter what you feel like, you don’t stop or give up. Research has consistently shown successful performers have high levels of achievement and competitive orientations. They also use ‘associative’ (monitoring physical sensations and breathing) compared to ‘dissociative’ (thinking of family, friends, work) strategies.
  3. Expect delays and problems regarding the day of the swim and the actual swim.
  4. Break the swim into smaller sections. Set goals for each and work toward them in training and during the swim. Most broke the swim into the a) Beginning – fun and exciting b) Middle – challenged to stay mentally focused in face of pain, being alone, cold c) Finishing – elation, letdown time goes quickly.
  5. Ensure your support crew are people you trust and are positive influences during the swim.
  6. Work on strategies to manage the pain of cold water.
  7. Plan in advance where you will stay, how you will train, and what to do in emergencies during both training and the swim.

Benefits of Cold Water Swimming

Both recent research and anecdotal research over many years suggest a number of benefits of cold water exposure. These include:

  1. Psychological benefits (sense of achievement, social inclusion)
  2. Green-blue therapy – being in open spaces (green) or open water (blue)
  3. Improved immune system function
  4. Less upper-respiratory tract infections


I hope the above gives some tips for open water swimmers. And some warnings. Particularly for masters swimmers or triathletes that may have cardiac issues or histories. The bottom line is that if the rules allow a wetsuit to be worn, wear one in cold water and ensure the arms and head are covered as they are big heat losers, along with the groin. If not, ensure during preparation that you get used to cold water by gradually adapting to it by training more regularly and for longer in water temperatures that you can gradually lower if possible. Also be aware of the need to gradually enter and exit the cold water slowly to reduce the risk of cardiac issues. One day I may see you at the Dardanelles where Lord Byron swam from Europe to Asia in 1810. A bucket list item for this old fella!


  1. Bergeron, M and others (2012) International Olympic Committee consensus statement on thermoregulatory and altitude challenges for high-level athletes. British Journal of Sports Medicine, 46: 770-779.
  2. Hollander, D & Acevedo, E. (2000) Successful English Channel Swimming: The peak experience. The Sport Psychologist, 14: 1-16.
  3. Makinen, T. (2010) Different types of cold adaptation in humans. Frontiers in Bioscience, S2: 1047-1067.
  4. Tipton, M. & Bradford, C. (2014) Moving in extreme environments: Open water swimming in cold and warm water. Extreme Physiology and Medicine, 3(1): 1-11.
  5. Tipton, M. (2016) Environmental extremes: origins, consequences and amelioration in humans. Experimental Physiology, 100(1): 1-14.
  6. Tipton, M.J. and others (2017) Cold water immersion: kill or cure? Experimental Physiology, 102(11): 1335-1355.
  7. (see how Olympic Swimmers cope with cold water immersion as part of an experiment. Very enlightening and interesting YouTube clip).