I coach beginning swimmers, and whip kick, or breaststroke kick, is probably the most frustrating skill to teach, mainly because the motions that the legs go through are unnatural. The biggest problem I see is the kids don't turn their feet out at the top of the kick, and therefore they cannot rotate
their feet around in a circular motion. Instead, they just end up straightening their legs, with no rotation. I can try to correct this through physical manipulation of their feet, but until they are able to go through the motions by their own doing, they won't remember the kick.
What I need is a device that can be used on land; one that will require the swimmers to turn their feet outward, and also will signal to them when they fail to do so.
What I think would work, is if I took two fabric cords, put an exceedingly thin, rigid, teflon coated toe-loop at the end of each, and attached the non ring ends to a central node, to create something that looks like:
Inside this node there is a spring loaded mechanism that pulls the cords back inside the node, akin to the mechanism that pulls the cord on the lawnmower back after you've started the engine, or the seatbelt back under the seat when you let go of it. There would be two such mechanisms, one for each cord.
My theory is as follows: if the kids turn their feet outwards at the top of the whip kick, they will be able to pull the cords out with their big toes, because the rings will catch between the big and second toes. The device will also provide resistance to notify them that they are kicking correctly. If, on the other hand, the kids fail to turn their feet outwards and kick down without rotating, the device will simply fall off their toes, because of the low friction, and the fact that there is no force to hold the device up.
This contraption might require some sort of toe-wedge to keep the swimmer from grasping the ring with his toes.