"Heart rate measures the intensity of your intention," says Hunter Allen, founder of Peaks Coaching Group. While the most valuable data for endurance workouts are time and distance – these are what measure your success in the race after all – knowing your heart rate keeps you honest. "Even if I see your pace and distance, I don't really know if you're going hard or not," says Allen. "High heart rate tells me your intention is high." All you need is a cheap heart rate monitor and the willingness to do a little math. Here is how Allen calculates his athletes' zones.
First, calculate your threshold heart rate. This is the highest average heart rate that you can maintain for about 30 minutes. To find it, run, cycle, or swim, pacing yourself to go all out for 30 minutes, as in a race. The average heart rate in the last 20 of that 30 minutes is your threshold heart rate.
Next, establish your zones. To do this, you need to calculate the percentage of effort according to a training chart. Allen breaks it down into Active Recovery (easy) at less than 68 percent; Endurance (for long distances) at 56 to 75 percent; Tempo (moderately difficult) at 76 to 90 percent; Lactate Threshold (race pace) at 91 to 105 percent; and VO2 max (all-out burst) at 106 to 120 percent (see Allen's full chart, below).
Use your zones in workouts. "I like to talk about heart rate in terms of energy systems," says Allen. "You're trying to train a system in order to improve the efficiency at that pace." If you want to improve your lactate threshold, in other words, you don't want to go out and do 60 minutes at 90 percent of threshold, says Allen. That's not actually hard enough to challenge the lactate system or cause enough stress to make it strong. Instead, you need to do intervals that are 10 minutes long and you need to be about 105 percent of the heart rate. Not ready to set your own heart rate plans? Go to a coach, or find a pre-existing plan and use your heart rate zones to keep you honest in the workouts.
Finally, recalculate, and do so often. Allen suggests testing your threshold heart rate every six weeks. "Most fitness adaptations occur in six- to eight-week cycles," he says. So try to do it every six, because you never know where you are on the scale and you might end up missing an adaptation if you wait longer.