You can use your imagination to think what super-slow-motion swimming might be like – it’s whole stroke swimming, but we can consider it to be a drill because of how it slows your movements down and makes little details in body position and stroke more apparent. It gives you more time to notice and alter parts of your stroke.
It’s like using a very slow tempo to restrain the speed of your movements to an exaggerated degree. There are no pauses in the stroke, just slower, very careful movement through the stroke cycle.
This slow-motion stroke challenges you to hold your best streamline and stable shape through the whole stroke cycle. You will get more length per stroke if you do, or you may find that when the stroke is slowed down like this, it exposes areas where you are disrupting your balance or streamline shape.
You would use stroke counting to see how far you can lengthen the stroke using certain adjustments to your form or movement pattern. If you keep all other parts of the length equal (your push off and glide distance, the amount of pressure you apply in each stroke, etc), you can get an idea of how these adjustment help or hinder your stroke length – making it easier or harder to slide through the water.
This drill may be suitable for warm up, cool down, and any time you want to work on very fine details of balance and streamline and test them with stroke count.
It is also possible to use short fins in order to provide a bit more velocity so you can slide through the water while moving the arms so slowly.