Cardiac Drift at B2B

In Base Building for Cyclists, Thomas Chapple states, "Usually both heart rate and RPE will gradually climb during a long, challenging, steady-state effort, even when power level stays constant. This increase in heart rate is referred to as cardiac drift...if you combine heart rate, RPE and power, you have three great measuring tools to help you dial in your effort levels.

To reach your best sense of pace and effort, the more sources of information feedback you use the better. You should train with these so you become intimately familiar with how your body responds to various effforts. I advocate training with a HR monitor because you get very good and learning to read the body; a little bit of understanding will help you interpret and utilize HR feedback.

In the pool you are mostly limited to the pace clock and perceived effort. On the bike I use HR, speed, and cadence. I think you get enough information to judge pace effectively without a power meter, but these have become very popular. In running I pay very close attention to HR and perceived effort.

Swim: 47.21 (hey, it's B2B) 148
T1: 6:14 142
Bike: 5:05:10 126
T2: ~2:00 105
Run:

7:33 128
7:25 129
15:48 128 (2 miles)
7:06 132
7:31 133
7:20 136
7:49 136
22:00 140 (3 miles)
7:20 141
15:08 142 (2 miles)
7:31 143
14:45 145 (2 miles)
7:03 145
7:24 143
7:29 144
7:33 144
7:22 142
7:35 143
8:00 140
7:58 140
~9 minutes 141 (last 1.1)

I think the marathon splits provide a very clear illustration of pacing and cardiac drift. It is true that the pace felt VERY restrained at first and then gradually became more effortful. So RPE increased, HR climbed as much as 17 bpm, and pace held very consistent. I should add that the weather was around 70 degrees and sunny for the run, you could expect even more cardiac drift on a hotter day.