You may use a Tempo Trainer to challenge your control and movement in faster-than-normal motion.
You do this by gradually increasing the tempo, until your stroke becomes uncomfortably fast. When you are forced to make the movements very quickly and count strokes to measure, it can expose weaknesses in your precision and strength that you may not notice easily when moving at normal and slower tempos.
When you first start increasing tempos away from your comfortable tempo (TC) you may be able to hold the same stroke count (SPL) for a few steps. But at some point in increased tempo you may not be able to resist adding strokes to you SPL. But why? Is it a matter of strength? A matter of your ability to hold precise movements? That is what you want to use faster-than-normal tempo sets to discover.
What tempo starts to feel fast to you is quite personal and depends on what you’ve been training with. You can shift your comfortable tempo range a bit over a few weeks with a systematic adaptation process. This is not nearly as difficult as shifting your SPL range, but it still requires a gradual process over time.
When you work into faster-than-normal tempo range, the harder it becomes (i.e. the more failure you experience) the more incremental the steps of increased tempo need to be.
For example, while inside your comfortable tempo range you may be able to increase tempo by steps of -0.05 seconds and you don’t need any adaptation time – you can get by with 50 or 100m distance for each round. When it gets near your comfortable limit you may need to make the increments smaller by steps of -0.03 or -0.02 and provide more distance for adaptation at each step – more like 150 to 200m distance for each round. When it gets extremely challenging (where failure is 40-50%) you may need to make the increments just -0.01 seconds and provide even more distance for adaptation at each step – more like 300m or more for each round. When failure is over 50% it is too much.
You may read more about Mid-Swim Decisions to think about how you need to assess the challenge level of faster tempos and adjust your approach.