Front crawl kick is non-propulsive
October 17, 2017 at 11:42 pm #3285jamesFParticipant
This statement is made numerous times in the pedagogy and whilst I see no reason to doubt it I’ve been thinking about how to justify it when “flutter kick” clearly is propulsive when swimming with a float or in a streamline position. I’m not a fan of the “Oh, well, that’s just different” hand-wavey kind of justification.
My thoughts are thus:
The downbeat of a flutter kick is very hard to make propulsive either in front crawl or just kicking. The lower leg and foot may be in a position to apply a force to the water in a backwards direction, but the knee presumably has to drop first to allow this to happen, in which case the thigh will be subject to overwhelming drag forces. Perhaps the top of the foot and shin could apply a rearward force on the downbeat if it were lifted clear of the water on the upbeat, but then something else would have to come out of the optimal streamline position for that to happen, thereby creating more drag.
On the upbeat the sole of the foot (and perhaps the back of the entire leg, to some degree) is in a position to create a propelling force. I’ve not tried it in the water myself, but perhaps this is what generates the forward movement in pure kick. However, in the full front crawl stroke, the water around the foot will generally already have a rearward velocity component relative to the foot greater than can be achieved by kicking the leg up and down, so the foot can’t actually create any useful force on the water.
I know of people who claim to travel backwards if they just kick front crawl. If they have limited mobility in their ankles then possibly there’s no way to generate any kind of propelling force with the sole of the foot and all they actually create is a slight forward force with the front of the leg during the downbeat of the kick.
Is this a plausible explanation, or am I missing something?
JamesOctober 18, 2017 at 3:30 pm #3286ryanupperParticipant
You’re probably right. I doubt anyone will research “bad” kicking at this point in time. It’s also possible, for backward kickers, that the knee is leading the kick and the thigh is pushing water forward with very little backward propulsion from the lower leg. In this case, the lower leg is just following the knee rather than performing its own powerful movement. This would be hip flexion without any effort towards leg extension.
As for propulsive kicking, one debate point I’ve used is that when a coach requires a swimmer to get to the other side of the pool by only kicking then the swimmer must figure out a way to get there (or face the wrath of the coach). This in no way indicates that flutter kicking is propulsive in full freestyle. It is easy to see how much velocity is generated by kicking alone: have a swimmer start off the wall and begin kicking. Acceleration is minimal and they will probably purposely kick down and back harder to get their body moving. This is very much different than pushing off the wall and using the kick to maintain a velocity to the other side. And very much different than balancing pitch and roll of the body during arm swimming.
In terms of power and drag, the thigh may create drag but if the thigh moves into the drag position relatively slowly the energy loss will be minimal. If the lower leg and ankle/foot generate a powerful downbeat kick then forward propulsion will occur. This would be hip flexion coordinated with powerful leg extension and ankle dorsiflexion. I’m not sure how much the bottom of the foot will contribute to this on the upbeat during hip extension and ankle plantarflexion. The anatomical angles don’t seem right.
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