Thursday, July 02, 2015

Glide Is A Dirty Word

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This post is a re-visit of our popular (and detailed) 2012 blog post: Overgliding, Inefficiency And The Overgliderometer

Many well meaning swimmers and coaches talk about the benefit of 'gliding' through the water when swimming but have you ever thought what it actually means to glide?

A strict definition of gliding is to consider the time between one arm finishing a stroke finishing at the rear and the next commencing the catch at the front:

This 'gap between strokes' is the true 'glide time' when there is no propulsion from either arm and you are truly gliding down the pool.

Elite Glide Time

The interesting thing is that many elite swimmers look like they're gliding when they swim but what actually is their gap between strokes? The answer may surprise you. If we study footage frame by frame of greats such as Ian Thorpe, Rebecca Adlington, Michael Phelps, Katie Ledecky, Alex Popov and Sun Yang, the gap between their strokes is remarkably similar: between 0.10 and 0.20 seconds (see examples here and here).

1 to 2 tenths of a second is literally less than a blink of an eye and goes to show that although these great swimmers appear to be gliding when they swim they are actually barely doing so at all.

Your Glide Time

So what does it feel like to swim with a 'glide time' of 0.1 to 0.2 seconds? Do so and you are hardly aware of any gap between their strokes - it feels like you are stroking smoothly and continuously from one stroke to the next without any perceptible pause at the front.

If you have added a deliberate pause-and-glide into your stroke then it's likely the gap between your strokes is at least 0.4 to 0.5 seconds:

Classic Overglider: Glide time 0.45 sec, swimming speed speed 1:42 /100m
This gap is now long enough for large inefficiencies to be developing as you start to decelerate significantly and sink deeper into the water (creating additional drag) between strokes.

If you've really tried to emphasise the glide then your gap between strokes may be as long as 0.7 to 1.2 seconds  - in fact we define anything over 0.7 seconds as extreme overgliding. Now the stroke is becoming so inefficient it's unlikely you can swim more than a few lengths without feeling exhausted and having to stop for rest:

Extreme Overglider: Glide time 0.84 sec, speed 2:56 /100m

Notice has the swimmer has sunk completely beneath the surface creating huge amounts of drag and making breathing extremely challenging.

Getting Very Geeky

If (like us) you love your numbers and statistics then you might enjoy the chart we've plotted up below. This is the data from around 100 swimmers of all ability levels from beginners to Olympic champions. It includes most of the famous swimming demonstration clips on Youtube.

We plotted their swimming speed versus their glide time:

The remarkable thing about this data is the strength of the relationship. The longer the gap between strokes, the slower and less efficient the swimmer is.

Of course the real clincher for our argument against actively gliding is the circled region:

In that area would be swimmers travelling quickly and efficiently but with significant glide in their strokes. But there aren't any. None.

Glide Is A Dirty Word?

When we wrote the Swim Types website in 2010, we described 'glide as a dirty word'. Perhaps unsurprisingly we copped a bit of flack from old-school swim coaches for making that statement but perceptions in the swimming world have changed a lot over the last five years and now our argument stands largely unchallenged.

Glide is a term that has been used by well meaning swim coaches since the 1980s to encourage swimmers to lengthen out their strokes. However the reality is that when asked to glide down the pool swimmers overly lengthen their strokes by adding an intention pause-and-glide at the front.

As we have seen this deadspot is very inefficient and very hard to remove once the habit is ingrained. It also triggers other significant flaws in the stroke:

- Putting on the brakes
- The overglider kickstart

Far better that we explain to swimmers that the goal isn't to make the stroke as long as possible (elite swimmers don't). And better to avoid the word 'glide' because it too easily introduces a deliberate pause. Let's talk about 'range' or 'extension' in the stroke but not 'glide' - swimmers will be much better off for it.

Swim Smooth!

[After the original blog a few fellow swim geeks asked us why we plotted the data against glide time, not percentage of the stroke cycle. This is a more meaningful analysis because deceleration is dv/dt not dv/d-cycle.]

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