I have encountered two swimmers who have a problem with front crawl and back crawl leg kicks. Their legs kick too deep and wide apart when asked to kick. Also, the legs are as straight as a ruler, so the swimmer moves nowhere; any suggestions?
The alternating leg kick action for both front crawl and backstroke must be a relaxed movement. If the leg kick is tense or rigid, or in your words, as straight as a ruler, then the swimmer will not move through the water.
There must be a slight knee bend and a very relaxed ankle. Encourage your swimmers to ‘kick with floppy feet’ or make their feet ‘like fins’. This may encourage a relaxed leg kick and a kick that generates enough power to maintain some movement.
You could try them with some fins. Fins obviously help provide movement through the water, but their most important job, in this case, is to help the leg kick technique by forcing the legs to relax and kick with a slight knee bend and relaxed ankle. Then there is a chance that this technique will be maintained when the fins are removed.
The swimmers will definitely get a better feel of how they should kick and move through the water.
Also, kicking whilst sitting on the poolside can be useful as they can see their legs kicking and maybe compare with a correct leg kick next to them; they can see and therefore feel the difference in how the legs should be kicking.
They will then hopefully transpose this into a correct action whilst swimming along.