Friday, March 9, 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 good indication of how much someone glides within their stroke. Some swimmers have a slight overlap, with the front 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 freestyle is continuous, transitioning smoothly from one to the other without any dead-spots or pauses.

Even though 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 to 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.

Overgliders

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 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. 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. But 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!

18 comments:

Anonymous said...

While I have never done any video analysis of my stroke, I have noticed that since taking some time off last year for some surgery I have had a very difficult time getting back to the level of efficiency that I was at before the surgery. This post makes me wonder about my glide time. I do notice that I regularly "kick-start" before each breath. I have always thought of it as the metronome for my swim stroke, but now I wonder it it is a symptom of an overglide. If I don't have a good way to video myself swimming, do you have any suggestions on how to determine if I really am gliding and introducing an unnecessary pause in my stroke?

Carl at cehoeft01@mmm.com

Anonymous said...

Nice!

You removed the Arnies to show the trend clearer. Are there any Bambinos in the graph or only Swinger, Smooth and Overgliders?

Unilateral breathers often have an asymmetrical stroke. Can you spot differences in gap for each side for these swimmers?

shuber1 said...

thank you for the article...I would like to echo...what about us Arnettes...I am concentrating on that long stroke and have no crossover anymore and is there any way we can be included in this graph..my guess we would be at the bottom of the heap...if we continue our old evil ways...how do you measure this at a small local pool?

Anonymous said...

Hi there I am curious as to whether or not any analysis has been done for breast stroke?

Simon Griffiths said...

Hi Paul,
Nice to see what you've been talking about for ages backed up with some analysis.
Simon

Anonymous said...

Terrific analysis, REALLY interesting! I really like it when advices are backed up by real data.

Kevin in MD said...

This data in terms of time is pretty meaningless. You need to normalize for the stroke rate.

People who swim faster are naturally going to have a faster turnover. Meaning that the entire stroke cycle will take fewer seconds.

So then it is only natural that any given portion will take less time as well.

What we need to see is the PERCENTAGE of each stroke cycle between the finish of one stroke and the beginning of the next.

It might show the same thing, but right now with the gap in seconds only, there's nothing to see.

Coach_Morg said...

Love this! Really appeals to the swim geek in me! As a coach I'm constantly correcting bad over gliding habits that are being taught by other coaches. It's simple, informally profile your swimmers to determine their background and traits before they get in the pool. This linked with a quick ape index check. Bingo you know loads about you swimmer in less that 2 mins and will be able to coach them accordingly. Don't have 2 mins to spare then get them to fill out a questionnaire prior to joining the session. If Paul lets me I might share my guide to athlete profiling in one of his blogs!

Anonymous said...

Is the gliding a symptom or the root problem?

Pawl said...

Very interesting. I would also be curious about how this correlates with stroke rate, but I'm not sure Kevin's criticism is correct.

Kevin's assumption (which I also held initially) is that the whole stroke profile (how your body is configured as a function of time into the stroke) simply scales with the total stroke time. But your data make me think that, regardless of our overall stroke times, those of us who have better than .5 sec glide would do well to cut down this part of the stroke.

I swim around 2:10 per 100 (and I can swim 1000 meters continuously averaging under 2:20) and would like to get faster. I am guessing from your chart I am likely an overglider. Do you have specific drill suggestions for me to try?

Thanks very much!

sheila sekhar said...

I have the same question as Pawl. I have tried to speed, but it takes a lot of strength & is painful.How to build up stength to work fast?
thank you.

LincsquadDavid said...

As we are starting to get more acces to affordable underwater vid cameras are there any other tips on what to look for during a swim vid session?

Swim_butterfly said...

Good article.

I agree...gliding is always viewed as posing and doing nothing. Do you came up with a word to properly describe the "glide" in your article?

Thanks

mark said...

Hi, The analysis in interesting, but in addition to normalising for stroke rate, i think the swimmers should be segregated by distance as well. A fast stroke with little overlap might be sustainable over a short distance, but not over a long one. So if we remove sprinters or short course events from the graph, does the result stand?

Pawl said...

Following up on Mark's comment: Could we take a given swimmer and look at her or him at different paces and see how the position on the graph alters? I know this is more work for you! (But you do have that video of Jono at different paces.)

Michael said...

Hi Paul,

All looks very nice and causal and I like the approach - it makes perfect sense.

I'd like to take it a bit further if I may.

The basic three components determining swim speed I come across most, including from your blog and DVDs, are :
Speed = function (stroke length, stroke rate, drag)
You eliminated/reduced the drag component from your data by excluding inefficient technique (cross-overs/scissor kicks etc), and you know intuitively that the gap between strokes is probably a proxy parameter for stroke rate (inverse relationship) so it'd be really informative if you could:
1. Plot stroke rate vs stroke gap time
2. Publish the R squared values (coefficient of determination) from your data sets - especially on the speed vs stroke gap time.
Anyone with a stats background could help you out.

Cheers, Michael.

ps like some of the other commentators, I questioned the validity of comparing swimmers of highly variable fitness/strength levels, but is strikes me this is reflected in the higher stroke rates and lengths which élite swimmers can maintain over us ordinary plodders.

pps I like the rythmn and timing sections of the Catch Masterclass DVD. As you say it takes at least 6 repeats of each Development Session (I do 8) before you start to get a feel for the water - I'm actually starting to sense the water flow over and around my fingers on entry and catch phase depending on how I orientate them and when I choose to pull.

Phil S said...

Thanks, Paul. V Interesting. For us novices - me at any rate - there is some confusion between stretching long "torpedo" style with your "fish spear" entry and then holding too long and overgliding instead of getting the catch working. Your graph is really helpful in indicating what a reasonable time-lapse should be. Your tips are great and have brought my swimming to another level(from a v low base) - and given me something to think about in the pool! What this all helps with is finding one's own efficiency level - a sustainable pace for 1k plus swims. Cheers, Phil.

Adam Young said...

Hi Mark, to answer your question on stroke gaps versus pace. In elite swimmers it is actually the 200 and 400m guys who have a 0.2 sec (ish) gap between strokes whilst the distance swimmers (1000m plus) have smaller gaps (e.g. 0.1 sec) or some overlap. This is because the middle distance guys can use a powerful kick to push them through the 0.2 sec whilst the distance guys don't have to that option and so have to use a more continuous stroke style.

It seems counter intuitive doesn't it? Think of it like spinning a smaller gear on a bike, each stroke is less effort but you take more of them. This can be just as efficient as a longer stroke style. In open water it's more efficient because there's less opportunity to be stalled by waves and chop between strokes.

Hope that helps!