Those guys are nuts! :-)
I didn't know it was a bike trail. The maps I found were of road courses.
How did I find it? I think I did variations on "Venosc bike altitude" "Venosc bicycle altitude" and so forth and followed a few links.
It looks like that run may be the one they describe here:
http://www.venosc.com/anglais/vtt.php
=== begin cut ===
IN VENOSC
25 km of marked trails from Venosc to Bourg dÂOisans , and a downhill run from les Deux Alpes to Venosc In les Deux Alpes: Change in level from 3200 m to 720m
With the bureau des guides des 2 alpes, you'll cycle with a guide with your or our bike : initiation, perfectionnement, difficult rides!
From 20 Â for an half day . +33(0)4 76 11 36 29 guides2alpes@yahoo.fr
=== end cut ===
If that's not the run, it must be in the vicinity.
Cheers,
Scott.