While we’ve covered this many times before, it seems there’s always a need to rehash that a "straight-leg" flutter kick really doesn’t mean you don’t bend your legs.
Why Do It:
A slight bend in the leg in the flutter kick is necessary for a proper flutter kick and provides the foot with greater speed as it attempts to aid in moving you forward.
How to Do It:
1. While the goal of swim teachers in the use of the words "straight leg" is to get people to stop kicking with too much bend in the knees, this is not a literal term. It’s a teaching term and should be called "straighter leg."
2. All of these great swimmers illustrate the meaning of a straight-leg flutter. They keep most of their thigh shallow, and hidden behind the body, creating a nice, straight line through their torso to the thigh.
3. The knees bend the back of the calf upwards, again, behind the body, hiding the resistance of the set up of the kick.
4. Finish the kick with a short, sharp snap of the foot to full extension and NOW a straight leg.
How to Do It Really Well (the Fine Points):
When you watch these swimmers, notice a very important aspect of a great flutter kick… ankel flexibility. Each swimmer finishes with a pointed toe while dragging some air back into the water with the foot. The air that accompanies the foot enhances the foot speed required for maintaining a quick, consistant kick.
Remember, "straight" doesn’t really mean STRAIGHT… it means "straigter" when referring to your flutter kick.