Duplicate pages

Hello Maverick,
I have a problem of duplicate pages. I set 3 categories of tracks (hiking, mountain biking and aids). When I create a new track assign it to a category, of course, but Google "sees" all three versions. Here's an example (from Google Webmaster Tools):

/ gpx-mountain-bike/viewtrack/439-tutti-i-segreti-di-monte-beni
/ gpx-trekking/viewtrack/439-tutti-i-segreti-di-monte-beni
/ percorsi-con-ausili/viewtrack/439-tutti-i-segreti-di-monte-beni

How do I indicate that the main track (in this case) is that trekking, in order to obtain a better indexing?
Thank you, M.