Cardiac drift? To stay in Z2 or not?

x2

Don't know how or when you calculated your zones but it sounds like it might be time to re-calculate.  You can review this article - http://beginnertriathlete.com/cms/article-detail.asp?articleid=633 - that describes in detail how to do a field test.  It also suggests regular re-testing to keep zones current.

are you doing your runs at the same pace as before?  if you are then yes you should speed up since your fitness has improved and you should be going faster at the same HR.  this isn't necessarily cardiac drift as it is improved fitness.  cardiac drift is when you are in your Z2 power zone on the bike but pushing 180bpm instead of the usual 130bpm all while the effort feeling the same. 

The cardiac drift (increasing HR in the middle of a single long workout) happens a fair amount, especially once you start getting into those 90+ minute workouts. 

I play it by ear and time of season. If I'm feeling great, or I know that I should be sharpening in peak race season, I'll err on the higher side and start Z2, left it drift to z3 by the end, with a net average of high z2. 

If it's early season, and/or I'm feeling like I'm dragging, I'll start in Z1, and end up in Z2, for an average of lower z2.

As you get in progressively better shape, you'll get less and less cardiac drift. Also, hydrating well during the workout helps lessen the drift on those long workouts.

Originally posted by Snaaijer

Originally posted by Clempson

 cardiac drift is when you are in your Z2 power zone on the bike but pushing 180bpm instead of the usual 130bpm all while the effort feeling the same. 

I think what you're describing is best ascribed to bonking Cardiac drift is, as the name hints, a tendency of the heart rate to increase without actual increased intensity. Here's a good article: http://www.uni.edu/dolgener/cardiovascular_phys/Electronic%20Articl...

see bold. HR effort at 180 feels like normal effort at 130.  just because your HR is higher doesn't mean you are doing any more actual work.  which is why HR pacing on a bike is completely useless when you can actually measure your effort/output instead of a single random response by your body.

If your fitness has improved, but your pace is the same, then you are creating less 'stress' for your body (it should take less effort to go at that pace now than it used to when you would get to Z2 very quickly, or you will be able to maintain that pace for longer before you feel the effort level really increase).  If you create less stress, then you induce fewer adaptations--which is what drives improved performance over time.  Whether that is good or bad really depends on the workout, your goals, etc.