Tag Archives: limiting factors

Limiting Factors in Marathon Swimming – Part 2 – Environmental Factors

In Part One I covered the physiological limiting factors in marathon swimming.

The various environmental aspects of a swim are not insignificant. They are especially important in that they all lay outside the swimmer’s control and often even outside the control of the support crew.

Water Temperature


This is generally a known factor prior to a swim. Swims are either cool or cold water like the English and North Channels or warm water swims like Maui, Rottnest, Manhattan or Chloe Maccardels’ upcoming Cuba to Florida attempt. A few fall into an intermediate category defined more by the swimmer’s experience, such as the Catalina and Gibraltar Channels. Sudden changes in temperature are rare in marathon swimming and where they are possible they are also understood; such as South Africa’s west coast which is prone to sudden wide water temperature changes, and the California coast where the sudden transition from very deep water to a shallower continental shelf very close to the  mainland can cause cold water upwelling at the end of a marathon swim. Air temperature is obviously much more variable and a condition of the weather but extremes of air temperature are not usual during a swim. A five degree Celsius differential can be significant for a swimmer if such a drop is also accompanied with a breeze or wind which can sap the swimmer of body heat.


Lion's Mane jellyfish
Lion’s Mane jellyfish

The recent and future attempts at a distance and time records by necessity are held in warmer waters such as Cuba to Florida.  These water are home to jellyfish with debilitating stings such as Box Jellyfish. While the cold waters  of the North and English Channels are home to Lion’s Mane and Portuguese Man O’War’s endurance records are less likely and jellyfish stings in the English Channel are rarely more than intermittent, though the North Channel (the Mouth of Hell) can have miles of Lion’s Mane blooms, part of what makes it the ultimate channel swim. Attempts to swim in these waters divide swimmers in two ways: whether attempts should be made in locations not considered possible without additional protection or exceptions to the usual rules, and if so are jellyfish protection suits acceptable or the thin edge of a wedge that will inevitably lead to more overt (or hidden) performance enhancing suits? (See Evan’s analysis of his survey of marathon swimmers for an excellent overview of the contradictions of divisions and unity in the community).


The Man In The Grey Suit is a subject of great concern (and discussion) for distance swimmers. Not of any real concern here in the north-eastern Atlantic, they are a greater hazard in the warmer waters elsewhere, particularly California, the Caribbean, Hawaii, South Africa and Australia. The Cook Strait Channel swim in New Zealand is unique in having a shark evacuation rule. Shark cages have been used for marathon swims in the Caribbean and South Africa at least. Shark cages are however considered swim assistance as they increase the swimmer’s speed through eddy current drag. Other possible control methods include electronic shark repellents (whose effectiveness is not entirely assured or quantified), armed boat crew or armed or otherwise scuba diver outriders.


These are amongst  the most variable of environmental factors and therefore potentially also the most limiting. Because swimmers move slowly relative to even a sailing boat, we are vulnerable to slight deviations, miscalculations or just insufficient data, the most likely cause. Even in such a well-travelled and mapped location as the English Channel, especially for swimming, pilots will occasionally speak of tides arriving early or late or with a difference force than expected. Tidal currents are understood at a larger scale, hundred of years of navigation have mapped the seas for craft, not for swimmers. Tides act in a similar chaotic way to a weather system, which means that small deviations will always creep in. The only way to improve accuracy of prediction is to improve the data, and this is not practically possible or even desired for small tidal variations. As swims occur in less well-known or new locations, the likelihood of discovering unknown local variations outside marine charts increases. Half a knot current, barely detectable to a boat, is enough to deviate a swim over hours from a projected or necessary course.

Global tides
Global tides

Crew and boat

Any English Channel pilot will confirm that one of the most likely causes of unsuccessful Channel swims is poor selection of support crew. The most likely cause is mal-du-mer, seasickness. For some people seasickness is a completely debilitating ailment that can sap all willpower and strength and there is no way to know whom it will strike. The solution of course is to have experienced crew. Even this can fail because people experienced on powered craft will be at the mercy of the choppy water amplified on an almost stationary craft. Other crew issues can also arise, whether accidents or other illness. Anyone who hasn’t been on a rocking boat looking down on a swimmer is unlikely to understand! And not unknown are mechanical problems on the pilot-boat. Most pilots are by necessity practical mechanics able to address problems as they arise, but not all problems can be fixed with a wrench and hammer while rocking about on the sea.

Channel boat The Viking Princess
Channel boat The Viking Princess out of the water


Weather changes are the bane of English and North Channel swimmers particularly. Other Channels like Tsugaru and Gibraltar and Cook are also subject to constantly variable and unpredictable weather patterns. If you are used to the predictable weather of the west US coast, with morning offshore and afternoon onshore breezes, knowing your swim will almost certainly take place with a 48 window, the difficulty of allocating two weeks or even long (like the North Channel) and still being completely unsure of getting in the water is shocking. Weather constraints obviously ran the full gamut. In the North, English and Gibraltar channels the main concern is wind (and its effect on the seas). Fog can also be a problem with 2012′s Channel season infamously seeing three solos on one day abandoned within a kilometre of France for the first time in 137 years. I’ve warned previously that fog may be the most dangerous weather condition for swimmers. In warmer humid climes like Round Manhattan, and the Caribbean, lightning storms are a serious cause for worry, a swimmer or boat caught exposed out on the water is in real danger. Having to wait for or even postpone a swim is something many marathon swimmers have undergone and the mental pressure this brings is often not inconsiderable, which I will discuss further in the next and final part.

Coming in part three, Psychological Factors.


Limiting Factors in Marathon Swimming – Part 1 – Physical Factors

The northern hemisphere summer swimming season is on the horizon , though it doesn’t feel like it here in Ireland where we’ve been having the coldest spring “since records began” (that phrase we are all familiar with from the past few years).  there will be big swims, both attempted and successful. 

Before genuine and extravagant claims are made by ill-informed media covering swims about which they know little and understand less, I though it might be worthwhile to round up the limiting factors for ultra-endurance marathon swims that might help people to apply some criteria to help evaluate some of those swims. Limiting factors which constrain or control a process.

Limiting factors on marathons swims can broadly be said to fall into three categories, with further subdivisions in two of those three.

  • Physical
  • Environmental
  • Psychological

In this first part we will consider the physical limitations.

The Physical Constraints to long swims pertain to the individual swimmer and will be influenced by their experience, training, and preparation.

The god bottle
The god bottle

Energy: Often seen by non-swimmers as the defining criteria, Energy relates to the swimmer’s ability to keep swimming. For experienced marathon swimmers however this is not often the as critical as is seen from outside. Evan and I have covered marathon feeding aspects in the past, from mechanics to content and possible supplementation, but the simple fact is that a tested feed plan, appropriate for the conditions and swimmer, will usually provide the pre-requisite energy. Most marathon swimmers use concentrated carbohydrate as the primary feed, with electrolytes to keep the body’s systems operating.  Changes to this basic plan vary with the swimmer but as long as the swimmer can keep feeding, they will take in sufficient energy.

Digestion: There is often talk of vomiting amongst marathon swimmers. Many, and I am one, think it is worthwhile to get used to being able to swim if or even while vomiting. While many swimmers put the pre-disposition of marathon swimmers to vomit at the door of feed plans and high carbohydrate loads, I think there can be other possible causes, (though the body regardless of size can only process so much carbohydrate per hour). Additionally  there are also the small amounts of salt water that even very experienced swimmers can take in due either to the odd mouthful of choppy water, or salt spray in rough conditions. And which I think is important but unquantified, is the extended time in a prone position which could hinder digestion. Peristalsis, the contraction of internal muscles to move food through the digestive process, has been shown in studies to be independent of gravity for most positions (unsurprisingly, since the intestine leads in all directions). Though peristalsis in the prone head-down position was not shown to be statistically abnormal (i.e. the swimming position) those studies were of short duration.  It is possible, but undetermined, if a longer time period could cause a greater likelihood of digestive problems causing vomiting. Vomiting during a swim usually isn’t particularly energy-consuming , and can even be a relief for once-off incidences. But should the vomiting frequency increase  greater distress can be caused and lead to a collapse in energy.

Nothing_Great_Is_EasyStrength: Like energy, strength is often more considered a limiting factor by non-swimmers. Marathon swimmers don’t often operate on strength alone but more usually on continuous repetition obviously and on technique. Hundreds or thousands of kilometres of swim training act as low-repetition strength training and cause swimmers to have very strong (if not very defined) muscles. A typical training load of a thousand kilometres a year (some swim less, some swim much more) prepares distance swimmers physically. Marathon swimmer’s embrace of the Nothing Great is Easy aphorism is simply one of our ways of explaining that physical strength is not the most important attribute.

Typical English Channel swimmer with salt mouth
Typical English Channel swimmer with salt mouth

Salt Mouth: I’ve written on Salt Mouth specifically as being a serious limiting factor for long swims. In brief it is the build-up of salt in the swimmer’s mouth and throat which can in the worst cases lead the swimmer to be unable to feed or even swallow, and can cause the sloughing of the epidermis of the tongue and throat. It can be extremely painful. Only swimmers who have run into this can understand how painful it can be. With all the talk of stinger suits and shark protection, I think ways this problem is far more important for those willing to risk  extending the outer limits of distance swimming. When evaluating a long swim it is worth looking at the salinity of the region. Kevin Murphy’s record 53 hours in the English Channel was in a region of higher salinity and is one of the many reasons swimmers who understand this limiting factor hold Kevin in such high esteem. Swims in the Caribbean such as Chloe McCardels or Penny Palfrey’s Cuba to Florida swim attempts are also in a region of high salinity. The US West Coast is lower salinity that the US East Coast and the Mediterranean is higher than any of these.

Global ocean salinity
Global ocean salinity

Sleep: If you’ve ever missed a night sleep and spent the next day in an utter daze, one may find it hard to imagine that sleep deprivation in itself is not as much a limiting factor as one may guess. There are studies showing that the sleep two nights before a big athletic event is of more importance that of the preceding night. And the majority of English Channel swimmers start their swim in the middle of the might and will miss most if not all of sleep of the night before. Once actually swimming, and assuming the swimmer has the requisite physical and mental stamina, lack of sleep for a second night does not seem to be the most critical factor. Obviously scientific study of the whole of marathon swimming in low enough given the small numbers involved, but the numbers of people who have swum over 24 hours (the 24 hour club) is very small with no scientific study to speak of, and only inferences can be made. Key is probably the factor that the athletic endeavour of marathon swimming is well below the swimmer/athlete’s VO2 Max ability, (what the athlete is capable of at their threshold limit).

Stroke training
Stroke training

Technique: Marathon swimmers range in style and technical ability. Some are not at really graceful or obviously and some like Evan or Trent are elegant controlled swimmers. Most of us though fall in the the wider intermediate range. We train technique along with all the other aspects and just are there are different ways to skin a cat there are different techniques in swimming from a bludgeoning powerhouse to a smooth FLOWer. Excellent technique in itself is not a determiner of success in marathon swimming, but equally being a powerhouse swimmer isn’t either. Good technique though is much less likely to lead to an overuse injury during a significantly long swim. Slight stroke imbalances when repeated 30,000 times for an average English channel swim, or even more for more epic swims, accumulate tiny stresses in the body of the swimmer, especially the neck and shoulders, that could lead to injury during a swim.

Coming in Part Two, environmental limiting factors of marathon swimming.