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Speeding up towards the end of a dynamic, why?

Philip Fennell

Well-Known Member
Mar 23, 2014
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What's the theory/science behind speeding up towards the end of a dynamic (DYN or DNF) swim?

I've been having a discussion with some freedivers about what I observed when watching the recent CMAS European Championships. The commentator made a few references to this and it could be plainly seen in some competitors swims, mostly DYN, and in one case some guy went off like a rocket and left his safety having to sprint after him.

I'm not well versed on the physiology side of things so that would be interesting to understand. It's been said that:

I believe the standard justification for speeding up at the end among those who advocate it is based on the idea (which may or may not be correct) that a short period of intense exertion at the end of the dive will be biased towards anaerobic rather than aerobic respiration.
and also that:

Throughout the dive your dive response only gets stronger throward the end it's Soo strong that your muscles are not supplied with oxygen you are basically sprinting for free...if you go fast at the beginning of the dive then you oxygen consumption is a lot higher because your dive response is still weak
From a psychological perspective, if you are doing this then you are focusing on outcomes rather than the dive and that's not really where we want to be, is it?

It's seems a bit of an edgy thing to be doing, that would require a high level of self-awareness to instigate at the right time and so is not something to be advocated to or practiced by the inexperienced.

I'd love to get peoples opinions on this.
 

Jeroen Elout

New Member
Aug 29, 2017
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Philippines
It definately gives me some extra meters when speeding up on the end. Maybe its also þa way to distract once mind from the increasing contractions. It's like you know you just have few seconds left before you have to breath so might as well sprint and get these extra meter.
 

MarcinB

Well-Known Member
Oct 26, 2012
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Bialystok/Poland
Philip, from the physiological perspective the facts you quoted make sense. Speeding up at the end could be beneficial, but rather only to those who have strong vasoconstriction. If your dive reflex is weak, vasoconstriction will not be strong even close to the end of the dive.
 
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Philip Fennell

Philip Fennell

Well-Known Member
Mar 23, 2014
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...its also þa way to distract once mind from the increasing contractions.
@Jeroen Elout - As far as contractions go, I have only rarely experienced a contraction or two towards the end of a long DYN so I don't get a lot of feedback from my body in that specific respect. Therefore, I think, reliably judging the point at which to accelerate must be quite difficult.
 
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Philip Fennell

Philip Fennell

Well-Known Member
Mar 23, 2014
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...Speeding up at the end could be beneficial, but rather only to those who have strong vasoconstriction...
@MarcinB In a freediver, especially in the pool disciplines, what's the best indication of the strength of the vasoconstriction? Is it something you can eternally observe or something you'll feel yourself?
 

MarcinB

Well-Known Member
Oct 26, 2012
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Bialystok/Poland
Some people are able to tell exactly when it happens, but I'm not one of them. The only way we can estimate the strength of vasoconstriction is the degree of muscle fatigue. In addition, vasoconstriction is strongly correlated with bradycardia. So those who have strong bradycardia usually have strong vasoconstriction as well.
 
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Philip Fennell

Philip Fennell

Well-Known Member
Mar 23, 2014
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Some people are able to tell exactly when it happens, but I'm not one of them. The only way we can estimate the strength of vasoconstriction is the degree of muscle fatigue. In addition, vasoconstriction is strongly correlated with bradycardia. So those who have strong bradycardia usually have strong vasoconstriction as well.
Thanks. :)
 
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Philip Fennell

Philip Fennell

Well-Known Member
Mar 23, 2014
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In addition, vasoconstriction is strongly correlated with bradycardia.
@MarcinB, here is a plot (blue area is the actual swim) of heart rate (BPM) against time for a 166m DYN I did last month and you can see that, by the standard definition of bradycardia (heart rate below 60bpm), I become bradycardic about a minute into the swim.

TOP 2017-08-04.png


I would normally start to feel fatigue in my leg muscles from around 125+ metres, may be after two minutes into the swim.

In your experience, how does that compare with others you've seen?
 

MarcinB

Well-Known Member
Oct 26, 2012
259
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Bialystok/Poland
Actually in freediving physiology bradycardia is usually defined as a drop in HR below baseline. So in your case it probably started around 30s and later into the dive it drops to 50% of the basal level. However, your baseline HR was high, most likely due to stress, which significantly overestimates the extent of bradycardia if its expressed as a percentage. In my opinion the actual HR value (at nadir) is more important than the percent change. In your case its around 50 bpm which is not especially low.

Did you use bifins (if so flutter kick or dolphin kick) or monofin? It makes a big difference in how quick muscle fatigue develops.
 
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Philip Fennell

Philip Fennell

Well-Known Member
Mar 23, 2014
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Did you use bifins (if so flutter kick or dolphin kick) or monofin?
That swim was with a monofin (three kicks and a glide with nine kicks to a 33m length on a good day) and yes, my starting HR is higher than I would like and is something I plan to work on this coming season. I have recorded sessions where it briefly drops into the high 40s but that's it.
 

MarcinB

Well-Known Member
Oct 26, 2012
259
63
68
Bialystok/Poland
In a monofin (kick, kick, glide) I also usually start to feel some leg fatigue around 125m. However, how fast muscle fatigue develops depends not only on the strength of vasoconstriction but also on the individual tolerance to lactate accumulation. So in my opinion its more usefull to estimate the degree of vasiconstriction in a given person under different conditions than to compare individuals.
 
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Philip Fennell

Philip Fennell

Well-Known Member
Mar 23, 2014
187
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In a monofin (kick, kick, glide) I also usually start to feel some leg fatigue around 125m. However, how fast muscle fatigue develops depends not only on the strength of vasoconstriction but also on the individual tolerance to lactate accumulation. So in my opinion its more usefull to estimate the degree of vasiconstriction in a given person under different conditions than to compare individuals.
That makes a lot of sense and is really useful feedback, thanks very much.
 
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