Last 2 swim sessions our coach has had us do freestyle pull sets using a small kickboard between our legs like a pullbuoy. Not the large kickboards with holes for your hands, just one of those small-ish thin ones, about A4 size. Now, I normally swim only 3-4 seconds/100m slower with a pullbuoy than without, so my pullbuoy speed is not that different to my speed without a pullbuoy. However with these kickboard sets, I noticed I was swimming about 7-8 second/100m faster than full stroke, without the kickboard (and therefore about 10-12 seconds/100m faster than with a regular pullbuoy). Not only that but it felt very smooth and effortless. Because the kickboard is quite small and thin, you have to grip it quite tightly so there's no kick going on at all.

So what I'm curious to know is - why does this make such a huge difference, and what does it tell you about how I can improve my stroke? Obviously I know it's difficult without seeing the whole picture, but I am fascinated why this particular kickboard drill works so well for me, far better than a normal pullbuoy. Some more general information for background: I have a relatively good body position in the water (i.e. lower body doesn't drop much), but I do have a weak kick and probably quite limited rotation. I'm a long-time swimmer (since childhood) but only ever at club level, not too serious, so plenty of room for improvement. Current CSS pace is around 1:40/100m but looking to get back down to around 1:35 by summer if possible.

Oh, and I'm a girl :)