Bifin technique - torso twist or not?

[Porky Pig]

I have been taught by various instructors that I should have a fairly static torso when bifinning, with limited shoulder movement and spinal twist, aiming to begin the movement no higher than the hips. Of course, there is always a little torso movement, but you get the idea.

I recently encountered a new instructor, quite a senior figure in the community, who encouraged significant torso twisting and saw my fairly static torso as a problem.

I'm not sure what the right approach is. One of the joys of constant weight with bifins has always been the ability to let the legs work away and have everything from the waist up movement-free so that I can concentrate on equalisation and relaxation. On the other hand, twisting in the torso is quite a natural aspect of a bifin movement and I can't see any great problem with it.

What do you think?

 

[bboynaki]

What happens when you try to push someone away from you in space?

 

[Porky Pig]

You are right that there is a torque (a rotational force) exerted on the body during a scissor kick.

The question is whether the torso should stay fairly rigid (experiencing this torque as a single unit and hence rotating slightly about its axis) or whether it should twist in opposition to the torque and do work against it. Which do you think is correct?

I suppose one factor that enters the discussion is the number of muscles that are doing work. If the torso twists, then muscles in the torso will do work as part of the bifin stroke. If the torso remains rigid and does not twist, then those muscles will do no work (in the scientific sense); they will merely exert static forces to stabilise the torso. I'm not sure whether it is good to bring more muscles into the movement or not - views on this point welcome!

 

[bboynaki]

I think it is correct to keep the torso from rotating too much and instead to use the opposite leg to react the moment produced when kicked. That means that during the recovery motion of the fin you are not simply bringing it back to the starting position but somewhat pushing the water with the bottom of the fin.

 

[growingupninja]

You see the giant, wide kick and shoulder movement in some older videos. The wide kick is still emphasized in most schools... I am not really a fan, based on pool tests I have done it isn't as efficient as a tighter kick--turbulence causes the fin to act as a sort of brake when the kick gets too wide. I do favor a stiffer blade than many divers, which may be part of it. When doing a duck dive, or coming off the bottom, I may use a wider kick than shown here but after even just one kick cycle I go to the tighter movement. And when entering freefall or positive bouyancy my kick breaks down some since I barely need to generate any power anymore and am just relaxing.

And yes, I think a lot of shoulder twist indicates poor core strength and inefficient up/back kick no matter what blade stiffness is used. While it may be more relaxing, it is force that is being transferred away from the means of propulsion (the fin/leg) and into the torso where it doesn't do anything useful.

I made this a while ago, but here is a breakdown of my own kick. This is in a pool but it is the same kick I use for depth in bi-fins. My current PB is 66.4 meters, wearing these fins, and wearing a 5mm suit (in warmer water I will probably up that quite a bit, big depth is not typically pursued in a 5mm)...

I do all my pool conditioning without weights, it forces me to pay more attention to forces, and forces a stronger back/up kick to counteract bouyancy.

 

[Porky Pig]

Thanks very much for your in-depth response. I naturally have a tighter kick, but have always been taught to go for a wider kick so that is what I have developed over time. Now I will have to continue to think about what is best!

It is really useful to have your video, because now I can be a bit more concrete in what I am referring to. Let's look at the slow motion bit at 0.16. When you begin to kick down with your right fin, your pelvis twists slightly relative to your upper back, so that the right side of your pelvis moves downwards and the left side moves upwards. This should increase the thrust of your kick (rather than dissipating force produced by your leg). In your case, the twist is very slight, but if you were given the choice, would you exaggerate, or further stabilise this twisting motion (or do you think you have it about right - it looks very natural)? If someone had very little to no twist, would you tell them to increase it?

 

[growingupninja]

I feel like the pelvic twist is right for me, and I have some 'knee break'. Too much is bad (i.e. 'bicycling'), but when kicking forward the leg needs a certain amount of relaxation to be powerful. A bit of pelvic twist I think is natural if you are using the large muscles in the thigh and hips which is where the kick originates. When teaching I tell people to think about just making the leg as long as possible, and it can help on the up stroke to consciously point the toe, almost like standing on tip toe. Powering up from the bottom I often feel like I am stomping--the up stroke can be very powerful.

I don't have the opportunity as much these days but for the first few years of my of long fins career I pounded out many hundreds of miles of DYN 50M laps, on an interval, and refined my own kick using the intervals as a (slightly) objective benchmark. This kick is what worked best for me as an ocean diver aiming to do many deep dives over the course of the day. I would recommend if you are serious to just do interval sets, i.e. my benchmark in the beginning was often 10x50M @ 1:30, meaning every 1:30 I would start the next one. That type of interval training will force you to develop efficiency and is better than the typical freedivers set where the only constant is rest time BETWEEN swims, which I don't think teaches you as much.

Have fun and be safe. It will probably help you a lot if you can get someone to film you. One of these days I am going to film a deep bifin dive for posterity.

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[Kray]

Do you combine dolfin kick with flutter kick when diving depth?

 

[growingupninja]

Sometimes. Descent on a line is always flutter and usually one arm pull as I reach neutral which will coast me to a nice free fall. Ascent is mostly flutter, maybe dolphin kicks with arm pulls at the end if it was particularly deep and my legs feel dead at the end. In a thinner suit I enjoy ascending with more dolphin kicks but in a 5mm all the power phases are flutter. Could also be habit since I have so much more time spearing in a 5mm.

When spearing I will usually pull a few times with the left arm on descent. Proper dolphin feels awkward to me with a speargun, although I frequently do lazy kicks as I am floating to the surface.

Lobster diving I use dolphin frequently for ascent, combined with arm pulls though since I am towing a virtual parachute up with me (mesh bag full of shellfish).

I used to like coming off the bottom with dolphin kicks but these days mostly use flutter.

Also could be a fin issue; in pool tests my max sprint in current fin is faster with flutter than with dolphin, my old stuffer c4's were fastest when doing dolphin.

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[Porky Pig]

Thanks again for another in depth answer!