The Anaerobic Threshold

The anaerobic threshold (AT) is the exertion level between aerobic and anaerobic training. The AT is the point during exercise when your body must switch from aerobic to anaerobic metabolism. The AT is a useful measure for deciding exercise intensity for training and racing in endurance sports.

During aerobic metabolism, your body creates energy by burning carbohydrates and fats in the presence of oxygen and produces carbon dioxide and water as by-products (breathing and sweating). Most of our daily activities are fueled by aerobic metabolism.

Anaerobic metabolism kicks in when exercise intensity is greatly increased, and the aerobic system can no longer keep up with the body’s energy demand. This is the point at which we cross the AT. During anaerobic metabolism, the body burns stored sugars to supply the additional energy needed, and lactic acid is produced faster than it can be metabolized. Muscle pain, burning and fatigue make anaerobic energy expenditure difficult to sustain for longer than a few minutes.

The fitter you are, the longer you can fuel your body with the aerobic system before the anaerobic system needs to take over. You can improve your aerobic efficiency—and thus raise your AT—by doing high-quality aerobic work at a level just below your current AT. Monitoring your heart rate and finding your Training Heart Rate Range (THRR) will help you determine what your current AT is.

Workouts to Raise the AT

Interval workouts are effective for raising the AT. For the best results, vary your workouts between aerobic work (where duration takes priority over high intensity), and higher-intensity intervals (where you will be just under or at your Maximum Heart Rate (MHR)). Aerobic work should comprise the largest percentage of your training. Here are a few interval workouts to try. We recommend long sub-maximal intervals, with roughly equal rest. As always, warm-up well before starting your piece:

  • 5 x 750 metres with 3 minutes rest
  • 4 x 1000 metres with 3–4 minutes rest
  • 4–5 x 5 minutes with 4 minutes rest
  • 5 x 4 minutes with 4 minutes rest