Question about Strength Training for an Ultra Runner

1--Try not to think quad so much as leg, even if you feel that these muscles are the limiter during downhill running.  Even then, try not to think leg so much as body.  Thus, proper core activation (strength/timing/balance of uppers vs. lowers, ext vs. intern obliques, etc) will be critical to help dissipate the load throughout the kinetic chain without excessive energy loss secondary to faulty/inefficient movement patterns and compensations.  But an exercise I might recommend would be jumps or exploding harvards or something from the plyometric drill section of my book (one legged versions more sport specific than 2 legged, of course).  What you want to look for is the ability to STAY in one place with minimal lateral or sagittal plane deviations--the better you can do this, the more stable you are (=better force production and alignment/less injury potential).  These movements also more readily replicate the movements speeds encountered in running.  Core recruitment is extremely high, too.  But, obviously, these are expressions of POWER and, thus, built on a foundation of strength, stability, and flexibility.  Lastly, know that as your training volume in-sport increases, your training outside of running will likely need to decrease.  Thus, proceed with caution with the eccentric loads mentioned above.  When in doubt, stretch and train the core.  And even before that, get the nutrition/lifestyle working for rather than against you.  That's what my next book is all about--hope to have it finished after RAAM this year (3 weeks away).