As Paul said above I've spent quite a bit of time studying the gap between strokes (when one stroke finishes at the rear to the next starting at the front) for all swimmers of all ability levels.
For elite swimmers the timing of their strokes varies from 0.1 second of overlap (where the stroke starts at the front just before the previous one finishes at the rear) to a 0.2 second gap. These are very short periods of time - which goes to show that although many elite swimmers appear to glide down the pool, it's actually an illusion, their propulsion is actually nearly continuous from one arm stroke to the next. We measure 'moderate' overgliders in the 0.4 to 0.6 seconds range and extreme overgliders right the way up to 1.4 seconds! As we pointed out in the blog post, the relationship between glide-time and speed is striking:
Any coach recommending people glide when they swim needs to take a close look at that data and what it teaches us about swimming efficiency. There's plenty of good things about the long smooth stroke of an elite swimmer - and we're great admirers of this stroke style - but it's a huge misconception to think that you create this by gliding down the pool. Once an over-glide is develop it's incredibly hard to change the stroke timing to lift the stroke rate - timing changes are one of the hardest changes you can make once they become ingrained. Even a super skilled swimmer like Thorpie struggled to change his timing slightly (as mentioned by Mike333 and discussed below). This is why we don't like teaching glide to anyone but especially novice swimmers, yes it makes their stroke longer but in all the wrong ways (see next paragraph) and once learned its a very hard habit to break.
There are three ways you can make your stroke longer:
1) You can reduce drag so you slip through the water more easily. Examples of this are improving your kicking technique, body position and alignment in the water.
2) You can increase your propulsion, so that the work you are doing is pushing you forwards effectively. Feel for the water, catch and pull technique are all good examples of this.
3) You can add a pause-and-glide between strokes.
1 and 2 are great ways to make a stroke longer - and when we see Ian Thorpe's silky smooth stroke in action (32 strokes per 50m) it's awe inspiring for these two reasons. However, if we add in the pause-and-glide then yes we make the stroke longer still but the swimmer becomes less efficient and slower because the stroke becomes accelerate-decelerate-accelerate-decelerate.
As we can see in the chart above, the drop-off in efficiency is extreme. As Paul mentioned above, Ian talks in his book about what happens if he tries to introduce a pause and glide into his stroke - he says he can get down to 22 or 24 strokes per 50m (incredible!) but he's much less efficient and slower as a result. He races at 32 strokes per length instead.
cottmiler wrote:Could there be a difference between acceptable gliding assisted by foot thrust and costly over-gliding where the body slows done and then has to be accelerated back up to speed?
Yes, the role of kick propulsion is an interesting one and definitely enters into this. Kick is a more continuous form of propulsion which helps maintain speed through any gap between strokes. The thing about a strong kick is that it can't be sustained over longer distances, which hints at the relationship we get between race distance and the gap between strokes. Three types of swimmer then:
1) Sprinters have to work very hard on the water and generate maximum power at a high stroke rate. They use a strong kick obviously but they can't afford to have any gap between strokes to keep the power output as high as possible.
2) Middle distance (200/400m) swimmers such as Ian Thorpe can still sustain a strong kick over this distance but are not looking for maximum power from the arm stroke. The strong kick allows them to use a slightly longer gap between strokes (only slightly) as it helps push them through the gap between strokes. These middle distance athletes tend to have the longest gaps between strokes of all, normally 0.2 seconds. Michael Phelps over 200m is another example of a 0.2 second gap.
3) Distance and marathon swimmers (800+m) cannot sustain a strong kick for long distances and so they reduce the gap between strokes again. This depends a little on individual preference, but we see gaps between -0.1 and 0.1 second.
So yes, using a very powerful kick (these guys can kick 100m with a board in 65-70 seconds) you can use a slightly longer gap between strokes, but only 0.2 seconds which feels very continuous from one stroke to the next when you do it - you can't perceive any glide being in place.
mike333 wrote:Did the pre-retirement Ian Thorpe overglide? In 2011 he said now that I'll being doing just sprints I need to learn to start my pull as my other hand is exiting the water whereas before I started my pull much later. Video of pre-retirement Ian Thorpe seems to back this up. So did he overglide? And if so, why?
Hi Mike, what Ian's talking about is trying to change his timing from 0.2 second gap down to zero to use more of a sprint style. This feels like a huge change to him (and in a way it is) but it's still a long way from the 0.4 gap for moderate overgliding out to 1.2 seconds for extreme overgliding!
The interaction with kick power can also be used to explain why distance swimmers use higher stroke rates than middle distance swimmers. Obviously power output over longer distances falls and so you might expect stroke rate to fall in line with that, but it doesn't. In fact it tends to increase again. Part of that is that higher stroke rates are more effective in disturbed open water but it's also related to the fact that it's not efficient to kick hard over longer distances and so a higher stroke rate has to be used as you can't afford a gap between strokes.
Hope that explains,