The term muscle memory is familiar to nearly anyone who has tried to develop athletic or movement skill. For years after I grasped that movement habits were formed by repetition, I had little understanding of the physical facts of how muscle memories were formed and where they were stored.

Now I have a more concrete grasp: We form them in the frontal cortex – the part of the brain whose massive development differentiates humans from other primates – and store them in the cerebellum, where simpler connections make retrieval of oft-used skills easier. I also understood that to replace an existing inefficient habit, it might be necessary to create a form of ‘muscle amnesia’ first before laying down a new, improved memory.

A new study by psychology and neuroscience researchers from Yale and Stanford addresses this phenomenon. They explain that it’s often difficulty to remember a new computer password or new phone number because the brain is competing to recall old and new memories that have many similarities. Using fMRI (functional magnetic resonance imaging) they observed that when the brain is cluttered with similar events, it’s difficult to recall one of them.

Memory competition helps explain why stroke drills may be more effective, in certain instances, than trying to ‘tweak’ your stroke. If you try to make a small change in the stroke, thousands – sometimes millions – of prior strokes with the old habit have created a powerful imprint, making it difficult for a new position, direction or timing to take hold.

It’s only by doing something your brain doesn’t associate with the old movement that you can begin creating a new imprint. Thus, the best drills need to be different enough from the habit you’re trying to break, as the examples in the video below illustrate.