Sustained Heart Rate & Running Threshold

Your anaerobic threshold is the point at which you're running at a sufficiently high heart rate to produce lactic acid faster than your body can clear it. When this happens, your ability to sustain your pace becomes sharply limited. By running at your anaerobic threshold, you train your body to more efficiently metabolize lactic acid, and over time your pace at your threshold becomes faster -- obviously making such workouts an effective training tool.

  1. Maximum Heart Rate

    • Heart rate is an essential guide to training because how fast your heart is beating is a direct reflection of how fast you're going as a percentage of top speed. It's important to know your maximum heart rate so you can intelligently design your workouts. For example, easy running is done at about 60 to 70 percent of your max, whereas if you race a 5K you're clipping along at about 90 to 95 percent. The American Heart Association recommends that you subtract your age from 220 beats per minute to get a good estimate.

    Aerobic Threshold

    • Aerobic threshold running is done at a heart rate at which you begin to accrue aerobic benefits -- improved cardiac output and oxygen transport to muscles, among other things. It also correlates with your easy or "recovery" pace. At this pace, lactic acid accumulation is minimal and the oxygen you breathe is sufficient to meet your energy needs, so it's a "pay-as-you-go" pace. According to USA Track & Field, your aerobic training threshold pace is approximately 65 to 75 percent of your maximum heart rate. A 40-year-old whose maximum heart rate is 180 beats per minute therefore has an aerobic threshold heart rate of about 120 to 135 beats per minute. Training at this pace increases your ability to run efficiently for long periods of time -- that is, your basic endurance.

    Anaerobic Threshold

    • When your ability to hold a true conversation starts to disappear and you can speak only in short bursts, you've reached anaerobic threshold. According to USA Track & Field, your anaerobic threshold heart rate is between 80 and 90 percent of your maximum heart rate, depending on your experience and fitness. Runs at anaerobic threshold are often called tempo runs; they're done at a pace most people could hold for about an hour in a race situation.

    Training to Improve Anaerobic Threshold

    • Improving your anaerobic threshold is perhaps the No. 1 way to improve your racing performances, so fittingly, there's no easy way to do it. Tempo runs can last anywhere from 20 minutes to maybe 45 minutes for seasoned athletes and can be done on a track so you can closely monitor your pace. Be careful not to race your workouts as this defeats the purpose. If you do these runs once or twice per week, you'll very likely see a dramatic increase in your ability to hold that pace for longer periods of time. You'll see your performances in 5K and 10K races improve by leaps and bounds, although marathoners may be the greatest beneficiaries of tempo runs.