Your neuro-muscular system remembers the patterns of muscle activity which you have done regularly, over an extended period of time. The longer you have been running regularly, the more easily it will be to start up when you’ve had a layoff. During your first few months of speed work, for example, if you miss a weekly workout, you will need to drop back a week, and rebuild. But if you have run regularly for several years, and you miss a speed workout, little will be lost if you start the next one very slowly, and ease into it. Be careful as you return to speed training, if this happens.