The Imaginary Athlete
To put all of this into perspective, let's take a look at an imaginary athlete, Joe. Joe's lactate threshold heart rate (LTHR) on the run is about 160-163. His zone 1 ends at about 137 beats per minute (bpm) or 84 percent of his LT. When training in a zone 1-2 workout, Joe should be running easy which is something I like to refer to as guilty pace! For him, that might be around 135 bpm, which would put him near the top of zone 1.
When running "steady," which is also called aerobic threshold (AeT), Joe is around 140 to 145 bpm. This puts him about the middle of his zone 2. This would be about right for an Ironman effort. After 112 miles of cycling, if Joe can maintain his "steady" running heart rate for 26.2 miles, he would, with all other factors being equal, be running the same pace as he had on his long training runs. That would lead to a pretty solid Ironman marathon time.
Training your body to work efficiently in zone 2 will help you keep your HR and pace even throughout an Ironman. This theory holds true for both the bike and run portions although most athletes will see somewhere around an 8-12 beat difference between their bike and run LTHR.
First of all, how does Joe apply the principles of "steady" heart rate to cycling? Let's say that Joe's LTHR on the bike is about 155 and his zone 1 heart rate ends at about 125 bpm or 81 percent of LTHR. When Joe trains on his bike and is riding easy his heart rate is in zone, right around 125 bpm. When he's biking "steady" he's around 135 to 140 which puts him in the middle to the top of zone 2.
With the exception of climbing hills, he shouldn't reach over 140 bpm in training when the workout calls for a "steady" effort. There are times that he might see 145 bpm on a steep hill, but that would otherwise be rare. Once again, these are his Ironman pacing efforts. In his Ironman race he will still have to run 26.2 miles after this 112 miles of cycling, so he won't be punching the accelerator at all on the bike if he wants to run well.
If you can follow the above recommendations, and practice the discipline of simply training "steady" when your coach assigns you those zone 1 to 2 workouts, over time you will improve your running and cycling efficiency and pace at less of an effort. These kind of improvements will pay big dividends on race day.
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