Here is one of the charts I used, which showed me how his cycling training went for the year, fairly clearly:
If you're looking for ways to prevent this from happening, then using technology in your training and analysis of your training will help you to make better training decisions. You can create training decisions based on data, not on peer pressure! After a few weeks of seeing a plateau, as a coach I would be changing training for sure!
This is the type of thing I discussed in the webinar on "Advanced Charts and Tracking in WKO+ for Athlete Performance," at Performance Webinars. If you use WKO+, or are interested in using it, then my webinar which is archived on there is something you'll want to see, for helping you see these plateaus before they happen.
I will share some more charts from this athlete and others, which show some interesting things from the year and season of 2009. Stay tuned!