While even veteran marathoners will benefit from keeping an eye on their heart rate while running, it's particularly advantageous to new runners because it allows you to gauge your running intensity. When you're a novice, you're apt to start off a little too fast — your heart rate will skyrocket, and you'll hit a wall before you've gone very far. Your heart rate can also tell you which zone you're in, whether it's aerobic (good for cardiovascular fitness), anaerobic (which increases lactic acid threshold) or your VO2 max (which increases your speed by increasing fast-twitch muscle fibers).
Finding Your Heart Rate
Choose from two formulas to determine your heart rate while running. For the first, subtract your age from 220 to find your maximum heart rate. For example, a 32-year-old's max heart rate would be 188 beats per minute — that puts you in the VO2 max zone.
The second formula, the Karvonen Method, determines your average running heart rate. This is determined by subtracting your resting heart rate from your max heart rate. If the 32-year-old runner's resting pulse is 60, subtract that from 188 to get a 128 average training heart rate.
Easy Runs and Aerobic Zone
When you're doing an easy run, such as during a long, slow run or a recovery run, your average heart rate should be around 60 percent to 70 percent of your maximum heart rate. In this zone, you improve your heart's ability to pump blood and your muscles' ability to use oxygen.
In the aerobic zone, a slightly harder run, your average heart rate is around 70 percent to 80 percent of your MHR. In this zone, your body's ability to transport oxygenated blood to your muscles and carbon dioxide away from your muscles improves, therefore benefiting your overall cardiovascular fitness.
In the anaerobic zone, you're running at a rate that kicks your heart rate up to an average of 80 to 88 percent of your MHR. If you want to improve your overall running performance, this is the zone you want to be in. It increases your lactate threshold, which is the point at which your body can't remove lactic acid as fast as it's generated. When your body hits it lactate threshold, you'll feel it — it's often referred to as "hitting the wall."
It takes a very fit person to train frequently at their VO2 max, and it should only be done for short periods at a time because lactic acid develops rather quickly. When you reach an average heart rate of 90 percent to 100 percent of your MHR, you're operating at VO2 max. Despite its difficulty, this zone is how you boost your overall speed, as it increases the number of fast-twitch muscle fibers.
The American Heart Association estimates the average maximum heart rates for runners based on age; however, the average heart rate during a run will still vary based on your intensity.
At age 20, AHA estimates average MHR at 200 beats per minute. This decreases to 190 at age 30 and 180 at age 40. It continues to decrease by 10 BPMs every decade through age 70, when the average MHR is estimated at 150 BPM.