A Kinematic Comparison of Dive Fins

[Bob Evans]

Hello, I asked a simple question on my Equipment Forum. What model of fin do you use?

 

[Captry]

OK, so some one else has a problem with my study.
Single subject... that is the problem, not really, the single subject was a competitive level swimmer with near perfect biomechanics. I say near perfect, because no one is perfect! The comparrison of intermediate and pro model Force Fins can be replicated by anyone with any other fins and you will still get the same results... that is what makes it good science.

If you are some one who dives something other than a Force Fin, I invite you to take my personal challange and dive a Force Fin. Once you have spent some down time diving a Force Fin, you will never dive another fin without comparing it to the ease and and comfort of a Force Fin. Did I mention the increased bottom time due to decreased O2 consumption.

I digress. I'll save that for another discussion thread. Please take my personal challange and dive a Force Fin. I will be happy to come out and dive it with you. If you do not have a pair of Force Fins, I will loan you one of my pair.

Safe diving,
Ryan

 

[Captry]

Thalassamania,

Hi there. You seem to have a real problem with my research. My science stands on it own. I am afraid you my just be afraid of something you do not understand. You continue to come back to my thread trying to rebuke the ease of divability of Force Fins. It's okay that you dive something else. Not everyone is going to embrace the "natural" biomechanical kick you get when diving a Force Fin. Some people are hung up on the "feel the pull" effect you get when swimming with conventional enclosed toe foot pockets. I am okay with that. I am just hereto share some solid science. You have a problem with single subject. My single subject was a competitive level swimmer with near perfect biomechanics. I say near perfect because no one is perfect. I invite you to take my personal challange and dive a pair of Force Fins. Really dive them. Dive them with an open mind and think about that biomechanics involved with the action of swimming as well as the "nature influence" of a Force Fin. I am not telling you that the fins you dive are bad. I am telling you that Force Fins take into account the biomechanics of the human body and merge it with the biomechanics of a sea creature, to make you as efficient as possible while you are swimming in the water.

Please accept my challange and give Force Fins and honest "college try". If you do not have a pair handy to dive with, I will be happy to loan you a pair of mine. I would love to go diving with you.

Please let me know.

Regards,
Ryan

 

[Thalassamania]

OK, so some one else has a problem with my study.
Single subject... that is the problem, not really, the single subject was a competitive level swimmer with near perfect biomechanics. I say near perfect, because no one is perfect! The comparrison of intermediate and pro model Force Fins can be replicated by anyone with any other fins and you will still get the same results... that is what makes it good science.

To be applicable to other divers (whose kick is, perhaps, no so perfect) the study needs to be replicated with other divers. What you are doing here is akin to studying the performance of, say, Giant Slalom skis (210s) and extrapolating the results of that study to the bunny slope where the skiers are much less skilled and typically are on skis that are about half that length. Sorry, but that's bad science. Not necessarily the study itself, which may have very limited application, but the application of the findings to subjects that are way outside the test group (individual).

If you are some one who dives something other than a Force Fin, I invite you to take my personal challange and dive a Force Fin. Once you have spent some down time diving a Force Fin, you will never dive another fin without comparing it to the ease and and comfort of a Force Fin. Did I mention the increased bottom time due to decreased O2 consumption.

I have made no comment on the utility or lack there of of the Forcefin, I have nothing for it, or against it, just on the conclusions that are being advanced on the basis of a study that clearly does not support them. If I took you up on your offer (and I expect that I will, if for no reason that to satisfy my own curiosity) and I found the Force Fin to be the best thing since sliced bread, that still would not change the inapplicability of the your study to the broader conclusions that are being advanced.

Thalassamania,
Hi there. You seem to have a real problem with my research. My science stands on it own.

I have no problem with the research, just with the extrapolation of your findings outside of your data set.

I am afraid you my just be afraid of something you do not understand.

I understand all too well, I am rather well trained in both statistics and exploratory data analysis.

You continue to come back to my thread trying to rebuke the ease of divability of Force Fins.

That is simple not the case, what I am debunking is the claimed applicability of your study to the divability of the Force Fin by the general public.

It's okay that you dive something else. Not everyone is going to embrace the "natural" biomechanical kick you get when diving a Force Fin.

"natural biomechanical kick" ... great phrase, but I one that I fear is scientifically and semantically empty. Since we did not evolve to to use fins, any use of fins is, by definition, "unnatural."

Some people are hung up on the "feel the pull" effect you get when swimming with conventional enclosed toe foot pockets. I am okay with that. I am just hereto share some solid science. You have a problem with single subject. My single subject was a competitive level swimmer with near perfect biomechanics.

Again, the idea that there exists a "new perfect biomechanics," for a physical action that we did not evolve to perform is rather bizarre. I'd suggest the use of a falsifiable term like "maximally efficient" instead.

... Did I mention the increased bottom time due to decreased O2 consumption.

The data to support this is?

I say near perfect because no one is perfect. I invite you to take my personal challange and dive a pair of Force Fins. Really dive them. Dive them with an open mind and think about that biomechanics involved with the action of swimming as well as the "nature influence" of a Force Fin. I am not telling you that the fins you dive are bad. I am telling you that Force Fins take into account the biomechanics of the human body and merge it with the biomechanics of a sea creature, to make you as efficient as possible while you are swimming in the water.

I am not claiming that Force Fins are bad, just that your study is inapplicable to the question of the potential benefit of the Force Fin to anyone except the single subject (and those who closely resemble him or her).

Please accept my challange and give Force Fins and honest "college try". If you do not have a pair handy to dive with, I will be happy to loan you a pair of mine. I would love to go diving with you.

Please let me know.

Regards,
Ryan

Any time you're in Hawaii,you are more than welcome ... and bring lots of difference fins, you find that I am very open minded but that at the same time rather demanding in terms of scientific rigor.

 

[Thalassamania]

Hello, I asked a simple question on my Equipment Forum. What model of fin do you use?

I have a trunk full of fins and I tend to select the fins that I use on the basis of the task at hand. My favorites are: Riffe Open Heel Long Blades, Idea3, three types of jets (SP, Farafin and IDI copy), DUckfeet and Avanti Quatros.

 

[Bob Evans]

Thalassamania, Thank you very much. I am always interested in what fin models some ones uses, specialty with your diving experience. Unfortunately all the fin models you are using now hang off your foot. I understand since I used the Jet Fin from 1966 to 1980. There is a night and day difference between what I design and the others. I see how the foot does not need to be part of the Aquatic world experience. Enclosing your feet is great if you're headed to Mount Everest, but please leave your foot on land. With 5,000 plus dives walking in water in your Jet Fins, your leg muscles have been trained. Using any of my fins will be such a freeing experience, you'll have to give yourself time to adjust. There is hope since my best Force Fin divers, those who are most evangelical about Force Fins came adapted from the Jet Age, but it takes time to adjust to moving freely and fluidly, with zero feeling from a smart fin.

 

[meesier42]

as to the validity of the study, as one should be able to tell, this study was not meant to be conclusive proof that all divers need to use Force Fins. The study was a proof of concept that used a control (experienced swimmer), a variable (pro and standard versions of 2 fins), and a measure of performance (ankle flexion/ROM), to prove or disprove a hypothesis. He uses existing information that showed that over use of the calf muscle and strain from over flexing the ankle with toes pointed are significant factors in swimmer cramps, sure a bibliography for reference material really is required to back the conclusion up.

To claim that using Force Fins reduce ankle flexing and ROM, thus alleviating a cause of cramping is a valid observation and the conclusion is valid, making the assumption that the reference material backs that claim up. To claim that this would transfer to other divers makes sense, although, I agree it requires the multiple subjects to validate the conclusion with statistical evidence.

the limits of this study, as I see it, only applies to swimmers with well trained kick cycles using a flutter kick. It doesn't say anything about the knee based poor excuse for a kick that most scuba divers use, much less divers using a frog kick.

I see this a something that I known for years, its just measured proof of it. It somewhat explains why the competitive swimmers that I have known through the years love FF and adapt to them in minutes rather than hours. it also shows why most people don't like them, because other fins have trained them to expect the negative feedback so their brains can falsely interpret their effort as speed/power, Bob calls this the terrastrial experience in an aquatic world. is the conclusion valid...absolutely, even if the report on the FF website is weak in showing it. Does it extend to all divers...maybe, extending the study to include many divers would help. Does it mean everyone in all situations should use FF...no

 

[Thalassamania]

Thalassamania, Thank you very much. I am always interested in what fin models some ones uses, specialty with your diving experience. Unfortunately all the fin models you are using now hang off your foot. I understand since I used the Jet Fin from 1966 to 1980. There is a night and day difference between what I design and the others. I see how the foot does not need to be part of the Aquatic world experience. Enclosing your feet is great if you're headed to Mount Everest, but please leave your foot on land. With 5,000 plus dives walking in water in your Jet Fins, your leg muscles have been trained. Using any of my fins will be such a freeing experience, you'll have to give yourself time to adjust. There is hope since my best Force Fin divers, those who are most evangelical about Force Fins came adapted from the Jet Age, but it takes time to adjust to moving freely and fluidly, with zero feeling from a smart fin.

All that may (or may not) be true, but it does not validate the study, and that was our topic of discussion. In point of fact it has no bearing on the study what-so-ever.

as to the validity of the study, as one should be able to tell, this study was not meant to be conclusive proof that all divers need to use Force Fins. The study was a proof of concept that used a control (experienced swimmer), a variable (pro and standard versions of 2 fins), and a measure of performance (ankle flexion/ROM), to prove or disprove a hypothesis.

The problems are many, ankle flexion/ROM has not been demonstrated to be a measure of performance, even for this single subject; There was no control, only an experimental subject; the subject was aware of what fin was being used at all times, so the study was not blinded; I could go on, and on, and on. As I have said before, the Force Fin may be the best thing since sliced bread, but the study does not pass muster from either an experimental design standpoint or in terms of rigorous statistical analysis. That's the cold, hard facts.

He uses existing information that showed that over use of the calf muscle and strain from over flexing the ankle with toes pointed are significant factors in swimmer cramps, sure a bibliography for reference material really is required to back the conclusion up.

His unsupported claims for what is, "over use" of the calf muscle or "over flexing" of the ankle lack any reference that shows that the measurements made have anything to do with either of those phenomena (or even that those phenomena exist) and he demonstrates no link between the alleged phenomena and cramping (which last time I checked had more to do with conditioning that with fin design, except to say that some fins are less likely to cause a diver to crap if said diver is in decent physical condition).

To claim that using Force Fins reduce ankle flexing and ROM, thus alleviating a cause of cramping is a valid observation and the conclusion is valid, making the assumption that the reference material backs that claim up.

No data to support such a claim is presented, no link between ankle flexing and ROM, as causes of cramping is either elucidated or referenced.

To claim that this would transfer to other divers makes sense, although, I agree it requires the multiple subjects to validate the conclusion with statistical evidence.

No, making such a claim is bad science and bad statistics. Using the findings of this study as a basis to design a more robust experiment is about it's only value as far as I can tell.

the limits of this study, as I see it, only applies to swimmers with well trained kick cycles using a flutter kick. It doesn't say anything about the knee based poor excuse for a kick that most scuba divers use, much less divers using a frog kick.

It does not say anything about anyone other than the single test subject.

I see this a something that I known for years, its just measured proof of it.

It is proof only that this one swimmer had a different response to two types of Force Fins and two unnamed other fins. Nothing more.

It somewhat explains why the competitive swimmers that I have known through the years love FF and adapt to them in minutes rather than hours.

That is an unsubstantiated anecdote, interesting ... but hardly meaningful in a scientific discussion.

It also shows why most people don't like them, because other fins have trained them to expect the negative feedback so their brains can falsely interpret their effort as speed/power, Bob calls this the terrastrial experience in an aquatic world.

That is a rather bizarre excursion into the substitution of semantics for science.

is the conclusion valid...absolutely, even if the report on the FF website is weak in showing it.

No, the concussion is not valid. As I mentioned earlier, the only valid conclusion is that this one swimmer had a different response to two types of Force Fins and two unnamed other fins. Nothing more.

Does it extend to all divers...maybe, extending the study to include many divers would help.

It doesn't even mean what you think that it means for the single subject. Figure out what it means for that individual, and then, perhaps, you can begin to design a meaningful experiment that would be meaningful for other divers.

Does it mean everyone in all situations should use FF...no

It does not even mean that the single subject should.

You guys don't get it. I am neither pro nor anti Force Fin or any other fin, I am just opposed to what appears to me to be the misuse of science in the service of kool-aid.

 

[Bubbletrubble]

@Captry: Ryan, please elaborate a little on the degree of scrutiny that was given your master's thesis. Generally, a master's thesis is not a peer-reviewed document. It is submitted to the Master's Thesis Committee (selected by the student and his advisor) and the document is "read" by the professors on the committee. (I place the word "read" in quotations since very few professors read a student's Ph.D. thesis, much less a Master's thesis.) They may offer up some suggestions for revisions...often they do not. Considering some of the language in the text and the content of the figures (lack of error bars, no tests of significance) included in the thesis, I question how closely they may have read the document. Committee input aside, the thesis is only submitted for publication in a peer-reviewed journal if it merits publication. While the study stands as marketing material for Force Fins to the lay person, any scientist with formal training would have serious questions with the work. I think Thalassamania has raised several interesting observations. One of the most glaring red flags is the "n" of 1. The brand and model of "conventional" fin was not explicitly stated. Weight and size of fin was not corrected for. Also, none of the data collected (ROM, vertical toe position vs. time, etc.) can be extrapolated to have any bearing at all on biomechanical stress. If relevance to cramping was hypothesized, then cramping should have been evaluated in the experimental design.

I don't want to criticize the work beyond this, Ryan, because I know you worked hard on it. I realize that you probably served as videographer. You spent a good deal of time in software data analysis. I think it's great that you've tried to explain how Force Fins change the kick of the person using the fin.

If a gear manufacturer is willing to hold up a piece of work as a "scientific study," then the company should be prepared for any valid scientific criticism that comes its way. That is the very essence of science. Force Fins may actually have a good design...but this study certainly doesn't prove it.

I think Bob and Ryan should be lauded for their willingness to allow others to give the Force Fins a try and "see for themselves." I'm not sure what to make of meesier42's posts. I suspect that optimal fin propulsion is fairly specific to the individual. Maybe how Force Fins work will just have to remain a mystery for now. (This is the Force Fin Manufacturer's Forum after all.)

I want to disclose that I have no conflict of interest here. I am not affiliated with any scuba gear manufacturer. I own no stock in Force Fin competitors. I'm just a Divebum with some training in academic science. I hope I didn't ruffle too many feathers here. It wasn't my intent.

For the record, I think this subject demands further discussion in the presence of beer...lots of it.

 

[Blair Mott]

All the interaction on this thread is great and I am thankful for all the posts! The feedback has been much welcomed.

The Force Fin is so unique that it should always be a subject in testing fins. Ryan is not the only one who has studied the effects on a human being moving a Force Fin through the kick cycle.


I am looking forward to finding out more about Dr. Harvey Barnett's study using Force Fins. I am not sure of the method details but I find his words very interesting. I do know he likes to Free Dive in them and he has an amazing story.

To all the members of ScubaBoard who have and who will contribute to this thread we thank you for your continued interest and support!