Cardiac Drift

Cardiac drift is basically when your heart rate increases during exercise with little to no increase in workload.  It's normal:  even over 30 minutes of easy running, your heart rate may go up 10-20 beats.  So heart rate rises while pace stays constant, and there is no harder effort, no heavier breathing, and notably no higher calorie burn. 


According to wiki:

Cardiovascular drift is the phenomenon where some cardiovascular responses begin a time dependent change, or "drift" after around 10 minutes of exercise in a warm or neutral environment without an increase in workload. It is characterized by decreases in mean arterial pressure and stroke volume and a parallel increase in heart rate. It has been shown that a reduction in stroke volume due to dehydration is almost always due to the increase in internal temperature. It is influenced by many factors, most notably the ambient temperature, internal temperature, hydration and the amount of muscle tissue activated during exercise. To promote cooling, blood flow to the skin is increased, resulting in a shift in fluids from blood plasma to the skin tissue. This results in a decrease in pulmonary arterial pressure and reduced stroke volume in the heart. To maintain cardiac output at reduced pressure, the heart rate must be increased.

 

Effects of cardiovascular drift are mainly focused around a higher RPE (Rate of Perceived Effort); that is, a person will feel like they are expending more energy when they are not. This creates a mental block that can inhibit performance greatly.

 

Prevention or minimization of cardiovascular drift includes consistently replacing fluids and maintaining electrolyte imbalance during exercise, acclimatization to the environment in which one is performing, and weight training[citation needed] to supplement cardiovascular efforts.

Cardiac drift is not a new concept to me.  I've trained by heart rate for at least half the year pretty much since the first year I was training for Boston. 


And I've had cardiac drift set in on long runs, and particularly on long runs with pace work, and 100% of the time when racing a marathon or even a half-marathon.


But yesterday I might have experienced something new...


Cardiac drift on a weekday?  On a short-ish weekday no less???


Is that even possible???


(At the outset, I'm ruling out dehydration or warm temps.  As I mentioned, I recently finished reading Megan's book, so I've been hyper-vigilant about hydration, and uh, it's insanely cold here right now.)


As I mentioned, I feel like my running is slooooowly coming back.  I ran a 5k a couple weekends ago and I managed to keep all my miles within a tidy little 5 second spread.  It was disheartening to realize that that little spread was slower than my half marathon PR pace (now just over 2 years old), and only a tad faster than my marathon dream goal pace (a pace I have never actually attained, but I still regard as goal MP). 


My running would certainly come back faster if I could lose some weight, but even staying right where I am (about 5 pounds over the top end of my "acceptable" range, and about 10 pounds over where I usually am, and where I prefer to be), my paces are starting to steady out and get a bit faster.  It has certainly been a long road back from my ankle injury (I actually still have 2 months left of wearing a brace for boot camp).  But I 100% feel like I'm improving, and I love seeing the progress.  Definitely feeling optimistic about the state of my running at present. 


So anyway, yesterday's workout was a taste of my least favorite kind of run -- progressive tempo.  Just a taste though.  Instead of a true PT run (which I really hate, and usually on my schedule is 4 progressive miles, plus 2-4 warm-up/cool-down miles), it was just 2 miles warm-up, 2 miles marathon pace (well, it's heart rate training, so not actually marathon pace, but the heart rate zone where you'd usually run your marathon), 1 mile in the next higher zone (equating roughly to half marathon pace), then 1 mile cool-down.


Written out, yesterday's schedule was:
2 mile warm-up
2 miles zone 3
1 mile zone 4
1 mile cool-down


How did my run go?  I basically started the pace work 1 mile early just to delay getting dropped. 


1 mile warm-up
2 miles zone 3 (first mile was just staying with my friends as they finished their warm-up, but it was pace for me, so I counted it)
1 mile zone 4
1 mile zone 5 (very bottom of it, zone 5A as it is defined on our schedule)
1 mile zone 4 (by chance, would have walked for a minute to bring down the heart rate and get back to zone 2, but as I slowed, a friend I hadn't run with since November caught up to me, so he and I ran most of the last mile in together; kept the pace easy, but the HR never really came down)


So on paper, that looks okay.  Not great since I have no business being in zone 5, but it does look progressive and it looks like I worked very hard.  (Pat on the back?  Not so fast.)


But when I look at the paces I actually ran yesterday, it's a different story:
1 mile easy
1 mile goal marathon pace plus 30 seconds (zone 3, in theory, marathon pace)
1 mile goal marathon pace plus 15 seconds (zone 3 still, in theory, marathon pace) (but I did stop for water in this mile, so it lowered my HR at least a bit, without water, I may have snuck into zone 4 already)
1 mile goal marathon pace (in zone 4 though, so in theory, should have been half marathon pace)
1 mile goal marathon pace plus 30 seconds (zone 5A, yow, zone 5A should be around 5k pace, not slower than marathon pace!)
1 mile easy pace, but heart rate still zone 4


See that bold mile?  Um, that's not good.  I mean, I shouldn't be running in zone 5A at all, but if I do, gosh darn it, that pace better be significantly faster than 10k pace, and likely faster than 5k pace.  And uh, yeah, this was not.  Not even close. 


So is it possible that cardiac drift set in to this extent after only 3 "tough" miles????  I didn't think it was even possible for that to occur in a significant way in far less than an hour.  Is there a chance I was essentially sweating plasma?  I wasn't even that sweaty.  I warmed up a lot (unzipped my half-zip top and took down my ear band), but I just don't know how much my core temperature could have really increased in the cold weather we're having.  I drank water once during the run (at about mile 2.1). 


But as I write this post, the answer stands out in my mind, clear as day now:  I need more lactate threshold endurance work. 


Sigh.  Just have to keep at it I guess...