Triathlon swimming: swallowing unpleasant truths

New research

Published last month in the ‘International Journal of Environmental Research and Public Health’, this study investigated the relationship between unintentional water intake while swimming in open water and post-race gastrointestinal illness in triathletes⁽¹¹⁾. The researchers hypothesized that the incidence of post-race gastrointestinal illness was related to the amount of water intake during the race but wanted to gain conclusive evidence, and calculate the risks involved, and see how risk varied with ingested water volume.

To carry out this study, the researchers recruited prospective participants of six different triathlons (where the swims ranged from inland canals to lakes) between May 2025 and September 2025 in four different cities in the Netherlands. In total, 1,294 triathletes were invited and then participated in the study. Following their event(s), each triathlete was asked to complete a medical questionnaire, which included questions about age category, sex, previous experience in outdoor swimming, chronic illnesses, athletic level (beginner, advanced, elite), the length and duration of the swimming leg of the triathlon, and unintentional water intake (UWI) during the swim. The UWI was defined as – ‘none’ or ‘yes’, giving number of sips - the key variable that the researchers wanted to investigate.

Importantly, this questionnaire also included questions about any illness during the seven days after the event. Where athletes reported a new onset nausea, vomiting, diarrhoea, or stomach ache in the days following the event, these were considered confirmed symptoms of gastrointestinal illness⁽¹²⁾.Other symptoms of illness were also recorded but were not included in the analysis as the researchers were only interested in GI illness. Regarding the triathletes’ estimate of their water ingestion, the researchers used a ‘sip-based’ reporting system, which has been shown in recreational studies to correlate well with actual volume⁽¹³⁾.

What they found

When all the data was processed and statistically analyzed, one of the most surprising findings to emerge was just how common unintentional water ingestion (UWI) was; over three quarters (75.3%) of the triathletes reported swallowing water during the swim leg of the race! In short, while many swimmers believe they can prevent UWI when swimming in open water, the physical demands in a race situation make this much more difficult in practice. Perhaps as expected, less experienced triathletes reported higher ingestion rates, likely due to less refined breathing techniques and lower confidence in choppy conditions. Less expected was the finding that male triathletes reported ingesting water more frequently and in higher volumes than women.

But how did the volume (number of sips) of UWI relate to GI illness risk? Here, the researchers’ hypothesis was proved entirely correct:

·        The average rate of post-race GI illness across all participants was 5.1%, but this rate changed drastically based on ingestion volume.

·        Where triathletes reported swallowing nothing, the rate of subsequent GI illness was a relatively low rate of 1.3%.

·        Compared to those who swallowed nothing, triathletes who swallowed between one and three sips of water during the swim were 3.7 times more likely to develop GI illness.

·        For athletes swallowing four or more sips, the risk escalated still further, with a 5.1-fold increase of GI illness compared to athletes who swallowed nothing.

·        When athletes developed GI illness, the most likely period for the onset of symptoms was during the first 48 hours post race (see figure 1).

In short, this study provided solid evidence that for every additional unit volume of water ingested, there is a significant increase in the probability of contracting a GI illness. The implication that follows is that even if the water quality is rated as ‘good’ in testing, athletes who accidentally ingest a high volume of that water might still run the risk of contracting a GI infection. When swimmers enter the water unaware that water quality is only average or even poor, even one accidental sip could deliver a nasty post-swim surprise.

Figure 1: Onset of GI illness symptoms after a race

Implications for triathletes and swimmers

The current water safety protocols set water safety limits for pathogens on the assumption that recreational swimmers ingest only around 20-30mls per hour. However, in open water swimming races and the swim legs of triathlons, the rate of ingestion is often much higher for the following reasons:

·        A mass start creates extreme turbulence and spray, forcing swimmers to inhale air that is essentially an aerosol of water containing potential pathogens.

·        Racing involves high-intensity swimming, which requires more rapid and deeper inhalations. If these occur at the same time a wave or splash hits the face, more water is likely to be swallowed.

·        During longer race swims, the total time spent swimming in the water is far higher than that typically accrued by a recreational swimmer taking a dip for 10 – 20 minutes!

For all these reasons, the take-home message is that it’s critical for open water swimmers and triathletes to try and reduce the volume of water accidentally swallowed, especially when racing. Here are some practical tips and ideas to help lower ingestion risk:

·        Try to create a continuous positive pressure in the airways by blowing a steady stream of bubbles from your nose or mouth the entire time your face is in the water. If air is exiting, water cannot be entering!

·        If you are a faster swimmer, you can benefit by practicing breathing in the bow wave trough directly behind the wave your head creates as it moves through the water. Breathing into this pocket of lower water level reduces the chance of suffering from the choppy conditions on the surface. Don’t lift your head out of the water to breathe - instead rotate it to breathe, keeping your mouth as close to the air pocket in the bow wave trough as possible.

·        Practice bilateral breathing, which allows you to breathe ‘away’ from the wind and waves. Breathing into the wind/waves will almost certainly result in UWI.

·        While drafting behind another swimmer in the water can save energy, it increases the risk of water ingestion from kick-spray. Instead, try to draft slightly to the side in a diagonal direction. However, take into account wind and spray direction – a strong crosswind or tailwind will likely send the spray away from you even if you are drafting right behind.

·        Unless you’re in the elite section of the race, you might be better employing a race start position on the outside edge of the pack, which avoids much of the spray and mist caused when dozens or even hundreds of arms and legs start flailing around violently in the water!

·        Using a nose clip can minimize the amount of water entering the nose. This water often drains into the throat, and may trigger a swallow or a cough (which leads to a deeper gasp). If you feel water entering the mouth, make a conscious effort to spit it out during the next exhalation. This is a technique worth practicing in training.

References

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