Enjoy the Liffey swim, the jellyfish stings and the faecal bacteria

Why do people enjoy taking to jellyfish-laden, bacteria-soaked open waters?

Making waves in the River Liffey. Photograph: Bryan O’Brien

On September 19th, the Liffey will be churned white by hundreds of swimmers forging a 2,200-metre path down the river as fast as they can. I hope the jellyfish have been ordered to stay out of the way. But that's just me voicing a feeble misgiving. The risk of coming face-to-tentacle with a venomous Lion's Mane will perturb few of that hardy breed who will part the Liffey's leaden waters to revel in the thrill of open-water swimming.

One of the fastest-growing mass participation sports, a recent medical journal reported that worldwide there are “more than 6,500 open-water swimming clinics, camps, tours, races and events in at least 158 countries”. And that’s not counting triathlons, where it precedes the cycling and running phases.

So, does open-water swimming represent some sort of harking back to a primeval urge for immersion in Nature at its most fluid? Possibly, though I should confess that as primeval urges go, it’s one I’ve found easy to resist. Homer praised water for being “clear, light, of high value, desirable’ . . . but then Homer never went anywhere near the Liffey.

Nevertheless, I would contend that Jack B Yeats's The Liffey Swim (1923), painted three years after the inaugural event, best celebrates our relationship with water. Mingling with the spectators' silent roar thundering out from the canvas, I sense an undertow of longing to be in there with the swimmers.

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Perhaps what’s stopping them – us – is the realisation that although we each have untapped reserves of mental and physical toughness, we seldom choose to explore their limits.

Beyond limits

Someone who explored beyond his limits (he drowned trying to swim across a whirlpool beneath Niagara Falls) was Captain Matthew Webb, once employed as a mate by Jack B Yeats’s fleet-owning maternal grandfather. In August 1875, Webb became the first to swim the English Channel, in a time of 21 hours 45 minutes. Almost a century later, in 1972, American long-distance swimmer Lynne Cox, then aged 15, made the crossing in 9 hours 57 minutes, breaking the world records for both men and women.

So I was interested to read a report in the Scandinavian Journal of Science & Medicine in Sports (2013, 23: e48?e55) which examined the gender difference in the performance of English Channel swimmers between 1875 and 2011.

A total of 1,606 (1,120 males and 486 females) made the crossing, and the average overall female swim time of 13 hours 12 minutes was about 14 minutes faster than that for males. However, between 1975 and 2011 the top three male swimmers were consistently around 10-12 per cent faster than the top three females, and the report’s authors speculate that this gender difference could be due to females having a lower skeletal muscle mass.

Like Webb and Cox, most swimmers accept jellyfish stings as part of the open water – oh, let's just give in and say it – "experience". For example, in a 2012 survey carried out by Dublin Swimming Club, 51.4 per cent of swimmers said they had been stung by a jellyfish during a race, although an addendum notes that swimmers can compete in more than 20 races a year and the number of stings is "genuinely pretty low".

Yes, but leaving aside jellyfish stings, as an award-winning hypochondriac my guess is that, depending on where you swim, the number of sewage-associated microbes that can’t wait to colonise you might be “genuinely pretty high”. Yet for those brave, salt-streaked children of Lir who can bat away a Lion’s Mane, if not a suspension of faecal bacteria, there are further challenges.

Hypothermia risk

The greatest medical risk associated with long-distance open-water swimming is hypothermia and, according to a review in the journal

Wilderness and Environmental Medicine

(2013, 24: 362?365), in an attempt to reduce the frequency of the condition, the Federation Internationale de Natation (Fina) – swimming’s international governing body – and the

International Triathlon Union

have established minimum temperature limits of 16 degrees and 14 degrees respectively, in which participants are allowed to compete.

However, the review's title surprised me: Heat Stroke Risk for Open-Water Swimmers During Long-Distance Events. Unlike when we exercise on land, and heat is dissipated via sweat evaporation, this doesn't occur during exercise in water. In addition, because conduction and convection are greater in water than on land, these can increase heat loss or heat gain during exercise.

So, if the water temperature exceeds skin temperature, a swimmer will gain heat and a subsequent rise in body temperature. On July 16th, 2013, at the Technical Open-Water Swimming Congress in Barcelona, Fina ruled that the regulation maximum water temperature for open-water swimming events is now 31 degrees, a temperature that's unlikely to trouble those preparing to slip into the Liffey.

But despite any landlubberly concerns I may harbour, there's no doubt that as far as all-round exercise is concerned, swimming is hard to beat, especially for those of us who are well into middle-age, as the title of an article in Current Sports Medicine Reports (2007, 6: 392-396) confirms, "Master's Swimming: An example of successful aging in competitive sport".

Similarly, "Swimming training lowers the resting blood pressure in individuals with hypertension" is the title of an article published in the Journal of Hypertension (1997, 15: 651-657), which concluded that ". . . swimming can be a highly useful alternative to land-based exercises for hypertensive patients with obesity, exercise-induced asthma, or orthopaedic injuries".

Good luck to all those in this year's Liffey Swim.