Wednesday, January 31, 2007

observations of the heart

Yesterday's workout called for five six-minute tempo intervals with two-minute recoveries (I cheated and allowed myself three-minute recoveries). As will likely be plain from the following figure, I did this workout on the trainer.

(red = heart rate; pink = power; green = cadence)

The interesting thing here, to me, is the interplay between time and heart rate over the course of the workout. Notice in the first interval I kept my power output around 270 to 280 watts, and my heart rate at the beginning of the interval abruptly rises to about 155 bpm, then slowly, and linearly, rises to about 170 bpm by the end of the effort.

In the next interval my power output is roughly the same, but my heart rate during this period moves from about 165 bpm to about 172 or 173 bpm.

Over the course of all five intervals this trend continues. In fact, my effort seems to flag in terms of power output, but my average heart rate over each six-minute period rises with each subsequent effort, topping out eventually at 183 bpm.

It doesn't take a power meter to notice this--I observed the same phenomenon last spring when doing intervals aided only by a heart rate monitor--but the graph does illustrate the point rather starkly.

You may also notice from the figure that (1) during the three-minute periods between intervals my recovery heart rate rises steadily--between the first and second effort it dropped to 125 bpm, but between the fourth and fifth it dropped to only about 138 bpm--and (2) in the recovery period after all intervals my average power output is lower than it was during warm-up, but my heart rate is higher.

An additional point worth making is that the third & fourth intervals felt much easier than the first two (though looking at the graph now I see that I apparently didn't work as hard on the fourth interval, so there's that).

So...it seems that that the body (or at least the heart) has to work harder to do the same amount of work later in a workout than it does earlier in a workout. That part seems intuitive.

However, if my perceived exertion is lower after a couple of warm-up intervals, that suggests that while my body has to work harder to do the same amount of work, under certain circumstances, my body feels better when it's working harder than it does at the beginning of a workout when the actual stress on my body (in terms of heart rate) is lower.

From that observation I suppose we can conclude that warm-up--an intense, race-pace kind of warm-up--is a good thing. But there's a balance. Do too much of a warm-up, of course, and you'll have no more juice for the real deal.

Anyway, there's nothing earth shattering here. The real lesson, or question, perhaps, is why does it take spending over a grand on a bunch of fancy shmiz to convince yourself of what you already knew?

2 comments:

vandyman said...

The phenomenon is called cardiac drift.

My understanding is that there are several factors that underlie the change: increased body temperature, dehydration, and reduced blood pressure. My guess is that perceived effort is more a function of your muscles being fully warmed up.

UtRider said...

I can't believe you rode the trainer for another hour after you completed the intervals... Seems like a waste of time to me. Get on, get off, get on with your life. Speaking of tempo intervals, did you see that Uhl did 95 minutes at 271 watts with an avg hr of 162 the other day? That dude can ride!