GoDiva (Online)

Hi,
Up till now I have mostly been diving while using very un-DIR Mares Avanti fins. Last four dives I have been allowed to try out somebody's "Jetfin look-a-likes" (so the black, stiff, short fins). He is willing to sell them, as he always had trouble with his knees when diving them (not DIR, but very open-minded and willing to try out stuff). He had 2 types, but both gave him the same problem.
My knees also seem to hurt more the last four dives (allthough I will have to have a go on one day with my old and "new" fins, to compare properly). This is during the dive, not afterwards; and my diving is not really big deco-risk diving (max 10-15 m usually, gradual ascents along the shore).

Have other people ever had this problem? Would this be due to the fact that these fins are not "the real thing", and therefore slightly different in some way or another?
I know, I should try out and compare myself, but I was just interested to hear some feedback.

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stach (Online)

If I'm correct, you are referring to the original beuchat jetfins.
they are "the same" as the "new" type

second : since when are mares avanti fins not dir? I thougt non splited fins was "the" way to go.
In my humble opinion : It is not because some people can't do backkick because the color is different and the name on the fins is different dat it is not dir right.
avanti fins are indeed not as stiff as jetfins but if the condition allow this then hy shoudn't it be good?

rjack (Online)

I have had sore knees early in my DIR career (from Jets). Frog kicking does take some conditioning, go slowly and carefully and listen to your body.

Richard

Rob H(Offline)

Hi GoDiva,

Here are my thoughts on the subject (from a physio's perspective):

I think that knees are subjected to strain from a combination of the frog kick and the rigidity of Jet fins. I have no evidence I can give you for this, and have not tried frog kicking in anything other than Jet fins, so cannot give a personal comparison. However, the action of the frog kick involves rotation and extension of the knee, which is mechanically similar to some orthopaedic tests to stress the knee cartilage. In addition, the rigidity of the Jet fins helps to provide strong propulsion, but consequently the knee rotates against resistance and undergoes strain - like performing an exercise with an increased weight. This is not an action that many people will perform naturally and needs some adaptation.

I found a similar strain on the knees when starting to frog kick but have found the situation improving with practice as knees have adapted to the task. I agree with rjack's opinion that this should improve with time, but while getting used to it listen to your body. If you try a couple of dives without frog kicking and don't have pain, you identify it as a possible factor. You can try with less rigid fins to see if that is different too. This wouldn't make me give up on Jet (or similar style) fins as they are a great tool for the job. But I would be aware of what the problems are and try to adapt slowly. This can involve regularly switching kicks to avoid one single kick for long periods and even trying some gentle resisted knee rotation exercises on dry land to help develop additional muscle strength. Quads and calves are used extensively in the kick too, so exercises to improve their strength will be beneficial and also provide more support for the knees.

So I think it is normal to feel something in the knees, although obviously it won't be a problem for everyone based on genetics, age, muscle power, etc.

Sorry if I send people to sleep with a really long and dull answer, but I analyse movement for a living and like to give an opinion when I know something about the topic area!

Hope this helps.

anders(Offline)

Well, I found them to light for drysuit diving.

I guess backkicks could be done with these fins, it's just a lot more difficult than with jetfins, as the avantis are so soft.

Apart from that, I was very happy with my avantis

Anders

MonkSeal (Online)

Are you sure you perform the proper frog-kick movements?

GoDiva (Online)

I have been doing frogkicks for most of my diving, and yes, I can do backkicks and helicopter turns with my old mares fins (even in dry suit). I borrowed "original" jetfins for my fundies last year, and can't remember noticing my knees, but perhaps I just was not paying attention to it then.

I can't remember the exact make of these "jet fins", and am with my parents for the weekend, but will check once I get back home.

Thanks for all your answers. And I'll have a go on a two-dive day with the two sorts of fins.

Rob: I do not think I really lack strength in my quads and calves (certainly not if muscle volume reflects strenght), and I bicycle to work whenever te weather allows (+/-12 km for a one way journey, admittedly not at high speed). Of course it might just depend on the way the musles are moved, but I will give it a try (all though I have grown to love frogkick, and don't like flutter kick anymore as it is not as relaxed).

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Brian Allen(Offline)

I also got some knee pain in the first few months of frog kicking with jet fins, but after a 2-3 months I didn't notice it anymore. I also started running at the same time so at the time put it down to this, but until your post I didn't realise that it was probably the fins. It could also have been poor technique at the start but it's impossible to tell now.

Like was said earlier it obviously takes some conditioning for the body to adapt. I no longer have any problem at all.

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PfcAJ(Offline)

It will definetly take some time for your legs to get used to the unfamiliar movements and resistance provided by the jet fins.

I took a 6 month hiadus from diving, and when I started diving a long time ago, I felt it.

Heck, I feel it now after really long (for me) dives!

Sterny(Offline)

I'd second all that - Avanti Quattros work, but for a DIR setup the jetfins are better - the weight gives you something at the end of your feet to use to adjust your trim by moving the position of your feet, and it's much easier back-kicking in jetfins than in Quattros (though you certainly can back-kick in Quattros, with a little practice).

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