Friday, March 09, 2012

Overgliding, Inefficiency And The Overgliderometer

You might have noticed on some of our recent videos how we've included a 'time between strokes' measurement in seconds. This is the time delay between one stroke finishing at the back and the next one starting at the front:

It turns out that this is a very interesting measurement because it's a measurement of how much someone glides. Some swimmers have a slight overlap, with the front of the stroke starting before the rear finishes and we indicate this with a negative number.

We have some clever video analysis software that lets us easily measure the time between strokes from video clips of swimmers and we recently spent a happy Sunday afternoon analysing hundreds of swimmers of all ability levels. As we were just interested in studying the effect of gliding on speed as closely as possible, we removed all the swimmers who were fighting the water (e.g. those with a large crossover in front of the head or a large scissor kick) from the dataset. They would have been in Region A below:
Included on the graph are famous swimmers such as Ian Thorpe, Michael Phelps, Rebecca Adlington, Sun Yang (1), Alex Popov, Grant Hackett, Lotte Friis (2) and Ross Davenport. It also includes professional triathletes (3) and most of the popular swimming demonstration clips on Youtube, as well as data from normal swimmers of all ability levels.

The relationship between gliding and efficiency is really striking isn't it? Wherever you are on the graph, if you introduce too much glide to your stroke you will slide down the relationship and lose chunks of speed and efficiency. In fact once a swimmer is over 0.7 seconds of glide (we catagorise this as 'Extreme Overgliding') they have become so inefficient they normally have to stop and take a significant rest every 50m:
Notice that there is a complete absence of swimmers in Region B, a region where fast swimmers with a significant glide would sit if there were any :
Many swimmers (and some coaches) believe that elite swimmers do have a significant glide in their timing but this is an illusion caused by the sheer length of their strokes - when you study the footage and take the measurements you find that there is hardly any gap between strokes at all. Their strokes are continuous, transitioning smoothly from one to the other without any dead-spots or pauses.

Even though our elite swimmers have a very small gap between strokes or even a slight overlap between them, this still gives a front quadrant stroke with the arms passing in front of the head (one over the water, one underneath). This is because the recovering arm travels quickly forwards over the surface as the stroking arm catches and pulls relatively slowly under the water.

Note that if you are going to study footage in this manner yourself, it's best to study clips where the swimmer has already swum 50m or further before taking the measurements. All swimmers can sustain a lower stroke count and swim quicker for the first 25m or 50m swum before settling down. You may have noticed this drop-off yourself if you've ever counted your strokes over several lengths.

Introducing The Overgliderometer!

Our graphics team had a little fun here but we hope the Overgliderometer makes a serious point, highlighting the transitions between stroke styles for different lengths of glide:

The Smooth Swim Type (e.g. Ian Thorpe or Sun Yang) have a very small gap between strokes of 0.1-0.2 seconds. The Swinger (elite open water swimmers and triathletes) have an overlap or tiny gap between -0.1 and 0.1 seconds, this stroke style is ideal for open water swimming where rhythm and momentum are key. The Classic Overglider (already losing a lot of efficiency) is in the range 0.4 to 0.7 seconds and Extreme Overgliders (very slow and inefficient) glide for 0.7 seconds or more.


In an effort to make their stroke as long as is physically possible, many swimmers have placed a heavy emphasis on gliding with scant regard for the rhythm of their stroke. Just like we teach that short scrappy strokes can be inefficient as the swimmer fights the water, so too is an overly long freestyle stroke detrimental to performance.

Some swimmers say that they like this 'mini rest' between strokes but given that water is over 800 times more dense than air, pausing and gliding only results in deceleration. Each new stroke then has to then re-accelerate the body in the water and this becomes very wasteful of your energy. It's also very common to see swimmers add a strange 'kick-start' action with the legs to re-start the stalled stroke. This adds drag and further harms your efficiency.

The term 'Glide' has long been used by swim coaches and is well meant to describe a smooth, efficient, unhurried freestyle stroke. Unfortunately it has also been misinterpreted to mean pause, stop and do nothing momentarily. Placing such a heavy emphasis on gliding with scant regard for the rhythm of your stroke is a huge mistake to make for your stroke efficiency. At Swim Smooth we avoid using the term glide as it is so easily misinterpreted to mean pause and do nothing.

Long Stroke Styles

Many swimmers aspire to have a long smooth freestyle stroke and that is fine for pool swimming as long as you create it in the right way and it doesn't become overly long. There are three ways to make your stroke longer:

1) Reduce your drag so that you slip through the water more easily
2) Increase your propulsion so each stroke pushes you further
3) Artificially elongate the stroke by deliberately pausing and gliding between strokes

Reducing your drag and increasing your propulsion (1 & 2) are clearly good things and will make you faster and more efficient. As we have seen in the data, trying to make your stroke longer by introducing a significant glide is putting the cart before the horse and only makes you less efficient. If you've tried Overgliding yourself, you'll know that it ultimately leads to frustration for this reason.

Be careful, there are still plenty of proponents of Overgliding on the internet today. If a long smooth stroke style appeals to you then like any swimmer you should work on reducing your drag, improving your propulsive technique and create a smooth rhythmical stroke without any dead-spots or pauses - just like elite swimmers do. This will naturally result in the optimal stroke length for you without chasing an artificially low stroke count by introducing a 'pause and glide' into your stroke.

If Long Doesn't Suit You

Depending on your individual make-up, a really long stroke style may simply not suit you. That's perfectly fine because a slightly shorter stroke can be just as efficient when drag is low and propulsive technique is good. However, what will make your stroke style unique is that you need a greater emphasis on stroke rhythm, perfect for punching through waves and chop in open water swimming. This is the refined Swinger style of stroke.

Swim Smooth!

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