Category: Swimming

The science of swimming is extremely complicated, involving the interaction of propulsive forces from the swimmer’s arms and legs and the drag caused by water. However, by applying new research courtesy of fluid dynamics and supercomputers, every swimmer can swim faster. Joe Beer explains…

Few sports are as precise as swimming. Cyclists can blame the wind, runners the terrain and team sports players the referee! Swimming, on the other hand, has exact distances and water is, well, constant. However, although ‘pure’ swimmers race in the pool and triathletes in open water (or OW as it’s referred to), the advent of long-distance swimming entering the Olympics in Beijing and fast-moving swimsuit and wetsuit technology means that many ‘constants’ in the world of swimming aren’t so constant after all.

The ‘sports ground’ for swimming (H2O!) is often quoted as being 1000 times denser than air. Trying to move efficiently through this very dense medium is not nearly as easy as other sports that take place through air. For example, top cyclists hit over 60kmh in short events on the track or in an end-of-stage sprint. Elite runners average over 30kmh for a quarter mile and over 40kmh at the end of sprints. By contrast, even the world’s best swimmers top just 8kmh (5mph)  over the 100m sprint. Yet that is still superhuman. Most fitness swimmers would fail to approach even half that speed. All that splashing around by even the most enthusiastic fitness swimmer is soon put to shame by the 12 year old who glides through the water with ease. In short, swimming is about brain not brawn, and it’s technique not triceps or trapezius size that matters.

To help ease the frustration that many people feel when trying to swim faster, this article looks at recent research papers and expert insight to glean some useful tips and tricks for swimming faster and more efficiently. In a sport where evolution of techniques, training knowledge and equipment are as meticulous as any other, there’s much to learn.

Drafting with a super computer

Computational fluid dynamics (CFD) emerged in the mid 1990s to investigate such areas as flight and propulsion in animals. These computers are loaded with page-long equations, performing millions of calculations per second to compute findings and produce models never before possible by pen and paper mathematicians. Experts keen on the science of swimming started using CFD to measure and understand better the flow around a swimmer’s body. The result has been that it’s increasingly possible to make models that can predict what is happening in the watery world that surrounds a swimmer.

A recent CFD paper presented by a group of seven experts from Portugal, although mind blowing in its mathematical methods, has produced conclusions that are both practical and written in plain English. Using complex equations, the group modelled the flow around two swimmers at varying distances from 50cm to 8m apart from one another. The flow speed was 1.6 to 2.0 metres per second, a rate that few but the fastest swimmers in water will ever approach, except maybe in a downhill water park ride!

The resulting pressure profiles of the two swimmers showed what you might expect, and maybe felt at times; that is, the lead swimmer has to work harder to deal with pressure caused by water resistance while the drafting swimmer has lower pressure to deal with(1). However, the most interesting finding is that the drag increases on the trailing swimmer as they move from 50cm behind the lead swimmer to around 5 metres. Thereafter any further increases in distance between swimmers makes no difference as both now exhibit the same drag.

As slower speeds occur in competitive swimming where drafting is allowed (eg age group triathlon with swimming speeds generally less that 1.25m per second) it may be that the effective draft zone is somewhat smaller for mere mortals and thus swimmers must stay much closer than 3 metres to get a ‘pull’ from a leading swimmer. Anecdotal perceptions from swimmers used to group and open water drafting suggest that as you move to within 2 metres of the lead swimmer’s toes, you start to feel a significant drop in drag. Data suggest getting as close as 50cm is best but up to 1.5m still results in a significant drafting effect (ie reduction in drag)(2).

The downside of this particular research was that the model used could only look at totally submerged bodies, which obviously is not a real-world scenario. It gives us some good clues, but the authors acknowledge ‘In the future we aim to evaluate active drag while the swimmer is kicking’. Other research data from the pool confirm the drafting effect. Swimmers who train in a pace line often choose to be closer than the required 5m that ‘should’ really be maintained between swimmers because they know it saves them energy. All except the lead swimmer can be on a much easier ‘set’ by close drafting.

If you draft, you go faster for the same effort or find it easier to hold a pace as your lactate (a blood marker of fatigue) levels are lower(3). In some cases it has been shown that blood lactate levels can drop by 33% if the trailing swimmer drafts correctly(4). This could result in a useful easing of mental effort or alternatively it saves some energy resources for a change of pace or higher speed effort later in the race (see figure 1 on heart rates and drafting).

Some of the most recent data presented on the concept of drafting from the Netherlands reports significant reductions in drag (and thus oxygen consumption) when drafting directly behind a lead swimmer(5). Swim to the side of the lead swimmer and the benefits are smaller. Most interesting of these findings was that the front swimmer’s kick can affect the benefit that drafting swimmers gain. It’s likely that higher velocities in the turbulent ‘kicked’ water actually raise drag around the drafting athlete. Put another way, if you find yourself being drafted, upping your kicking effort can make it harder for those behind. Kicking can cause half of the drag reduction the drafter was getting to vanish!

And finally, for triathletes who swim then bike, some interesting data actually shows that by drafting in the swim, it’s possible to improve subsequent cycling efficiency. Almost 5% more efficient cycling resulted when athletes drafted a lead swimmer compared to swimming alone(6). Remember this well by reading it several times; water is very dense so let someone else push it aside for you! Of course in ‘pure’ swimming galas and meets with one swimmer per lane, deep pools and anti-wave ropes means physical drafting is not an option.

Thoughts of a swimming coach

In theory, the trunk acts as a stable base on which to pull the swimmer forward whilst also stabilising the leg kick occurring behind. However, actually knowing what goes on when the front crawl swimmer is immersed in water is far from clear. These are the thoughts of leading UK swim coach Dan Bullock:
“I have long felt that good rotation (but not excessive) and a mechanically sound leg kick will provide the stable base from which to make better use of your arm-pull. You may have read or been lectured on the importance of ‘driving from the hip’ while swimming front crawl, and how this generates more power through the stroke. I have always found this hard to implement.

After swimming recently while using a pull buoy, I could feel how my pull was weakened, which made it harder to set up my catch. In several sessions I oversee I have noticed that the stronger kickers are also the faster swimmers. Not conclusive by any means but something to think about for triathletes! If you are swimming around the 24min mark for 1500m and are looking for the breakthrough to 21mins then this is most likely where the breakthrough will come from since the arms are unlikely to get much stronger or longer!”

Should you rock and roll?

One particular technique touted by some coaches as the key to improved propulsion is that of conscious additional rolling of the hips. This rolling of the hip region occurs to varying degrees dependent on what footage you see of which swimmer in a particular event. However, it has been suggested that voluntary and intentionally exerted body roll – for the purpose of generating additional propulsive forces – seems to run the risk of reducing the ability of the trunk to provide a stable anchor for propulsive movements in the upper and lower extremities(7).

It seems then that the ‘lead with the hips’ approach is incorrect for the swimming chain of events to proceed efficiently. There are even those who suggest everyone should exaggerate the roll as their primary focus. The problem with excessive roll is its effect on the time each stroke takes to complete and the likely increase in drag. Neither is a good idea if you want to be efficient, faster, or both. Hip roll is a consequence of good propulsion and not something that needs to be excessively forced to happen in order to try aid propulsion.

Swimming involves propulsive forces generated by the hand, forearm and upper arm pulling against the water, while the legs provide additional lift and propulsion. You can get quite a lot of propulsion from the feet but using feet is energy intensive; pure swimmers can kick like a motorboat but the triathlon community must watch this lower body energy use as they still have a bike ride and run to complete!

Suitable suits

The new generation of super tight, high-tech fabric swimsuits has caused a stir, with some saying that they give an unfair advantage. These range from full-length neck to ankle suits down to legs-only versions that look like a track sprinters’ bare torso training kit, but what they have in common is that independent testing has shown they do improve performance by reducing drag on the swimmer.

In a recent study, researchers took 14 competitive swimmers and measured performance, stroke rate and distance per stroke in normal, first generation full-body and legs-only suits in a 25-metre pool(8). In addition, a flume was used to measure drag. This is a moving water version of a wind tunnel, giving pinpoint accurate water speeds. In this particular study the swimmers were dragged with a rope hooked up to a load-measuring device without any arm or leg movement. This allowed drag from the suit to be isolated.

The suits tested were ‘first generation’ suits including the Speedo Fastskin, Arena Powerskin, Tyr Aquashift, ASCI and Nike Lift. These designs focus on reducing drag losses, and thus the buoyancy of the swimmers was not affected. This is significant because the very latest generation of suits, such as the arena X-Glide, are designed not only to reduce drag around the swimmer, but also to aid buoyancy.

A quick glance at the tumbling swimming records over the past five years and the suits lining up on poolside suggests something is happening that is not just a coincidence. After all, world-class swimmers have always trained hard and peaked bang on time, to suggest otherwise is missing the point – these ‘super-suits’ are super fast!

In the study above, the six freestyle distances timed in the pool (25, 50, 100, 200, 400 and 800m) were 2 to 4% faster in a full-body suit, and around 2% faster in a legs-only suit(8). Specific flume measurements suggest a 4-6% drop in drag is the main effect of these first-generation suits. For example, in the 100m, Pieter van den Hoogenband beat the legendary Alexander Popov’s time of 48.21secs  by three-quarters of a percent, in what we now call a first-generation fast suit. Moreover, in the last 18 months the 100m-world record has dropped more than it did in the 8 years from Matt Biondi’s in the 1980s to Popov’s in the 1990s.

The 100m world record time has dropped by 6.8% over the last 80 years whereas the time taken to swim 100m has dropped 19% in the same period, 2.6% of that in the past decade (see figure 2)! Over the last 40 years, 100m running times have improved by 3% but swimming times by a massive 11%!

However, the swimsuit options open to elite swimmers will soon be restricted. On 1 January 2010, FINA is bringing in stringent rules likely to kill off many super-suits. However, in the sphere of triathlon, where innovation is applauded, the improvement of swim technologies looks to herald faster one-piece suits for the elites swimming in non-wetsuit races and also to wetsuits themselves, which are often seen as a buoyancy aid.

Recent data using triathletes suggests that the wetsuits’ ability to improve swimming is down to propulsion efficiency through a gain in buoyancy and to drag reduction across the body(9). The use of a good fitting wetsuit, smart drafting and reasonable open water sighting skills helps to produce a fast and efficient swim time.

Summary

So there we have it. Drafting, a natural hip roll and a good swimsuit/wetsuit can all increase swim speed. More research is still needed into how to optimise all of these factors to aid swim speed and efficiency but whatever your aquatic goals, a little knowledge goes a long way to  helping smooth your path through aqua communis!

Joe Beer is a multisport coach (JBST.com) author of ‘Need to Know Triathlon’ (Harper Collins) and a successful multisport athlete in triathlons, sportives and time trials

References

1. J Sport Sci Med (2008) 7:60-66
2. Med Sci Sports Exerc (2003) 35: 1176-1181
3. Eur J Appl Physiol (2000) 82: 413-417
4. Med Sci Sports Exerc (1991) 23:744-747
5. Med & Sci Sports Exerc (2008)  41:837-843
6. Med Sci Sports Exerc (2003) 35: 1612-1619
7. Swimming Research (2007) 17: 39-44.
8. Med. Sci. Sports Exerc, (2008) 40: 1149–1154
9. J Sci Med Sport (2009)12:317-22