Anaerobic Threshold Calculator

The anaerobic heart rate zone is generally defined as 80–90% of your maximum heart rate (MHR). In this zone, your body can no longer fully rely on oxygen to produce energy and begins using anaerobic metabolism, which produces lactic acid as a byproduct. Exercising here improves speed and power but can only be sustained for short periods.

The anaerobic threshold (AT), also known as the lactate threshold, is the exercise intensity at which lactic acid starts to accumulate in the bloodstream faster than it can be cleared. It is typically expressed as a heart rate value, usually around 80–85% of MHR, and marks the transition from aerobic to anaerobic exercise.

The Traditional Fox & Haskell formula (MHR = 220 − age) is the most widely known and used by organisations like the American Heart Association. The Modern Tanaka formula (MHR = 206 − 0.88 × age) was developed from a larger dataset and is considered more accurate, particularly for older adults, as it produces a slightly higher MHR estimate.

The Karvonen method incorporates your resting heart rate (RHR) into the calculation using the formula: THR = [(MHR − RHR) × % intensity] + RHR. Because it accounts for your individual fitness level via RHR, it produces more personalised training zones than the Basic method. It is recommended for athletes or those who know their resting heart rate accurately.

Most people can sustain exercise in the anaerobic zone (80–90% MHR) for only a few minutes at a time. The exact duration depends on your fitness level, training history, and how deep into the zone you are. Interval training often uses short anaerobic efforts of 30 seconds to 3 minutes followed by recovery periods.

Several factors influence your AT, including fitness level, age, genetics, training history, and overall health. Regular endurance and interval training can raise your AT over time, meaning you can exercise harder before switching to anaerobic metabolism. Dehydration, illness, heat, and altitude can temporarily lower it.

The most accurate way is to measure it first thing in the morning, before getting out of bed, after a full night's sleep. Use two fingers on your wrist or neck and count your heartbeats for 60 seconds, or count for 30 seconds and multiply by two. A fitness tracker or heart rate monitor can also provide a reliable average over several nights.

The five zones are: Recovery (50–60% MHR) for light activity and active rest; Endurance (60–70% MHR) for fat burning and base fitness; Aerobic (70–80% MHR) for cardiovascular improvement; Anaerobic (80–90% MHR) for speed and power; and VO₂ Max (90–100% MHR) for maximum performance. Each zone targets different physiological adaptations.