Anaerobic Heart Rate Zone

Checking Heart Rate Monitor
Checking Heart Rate Monitor. Thinkstock/Stockbyte/Getty Images

The anaerobic zone of exercise intensity is 80% to 90% of your maximum heart rate. The heart rate beats per minute to reach this zone varies by age and individual fitness level. At this exertion level, you are breathing very hard and it isn't possible to speak in full sentences.

Pronunciation: an-er-oh-bic zone (noun)

Also Known As: Threshold zone

Common Misspellings: anarobic, anairobic, anerobic

Anaerobic Exercise Zone

This zone of vigorous-intensity exercise can be used to build your heart/lung capacity. In the anaerobic zone, the body burns more calories but mostly from carbohydrates rather than fat. At 80-90% of your maximum heart rate, 15% of your calories burned in this zone are fats, 1% are proteins and 85% are carbohydrates.

The anaerobic energy systems operate without oxygen (which is the meaning of anaerobic in general). They burn through ATP and then turn to anaerobic glycolysis, using glucose and glycogen for fuel with a byproduct of lactate. The body clears lactate as it produces it, but if you are creating more than can be cleared from the muscle being exercised, you have reached your anaerobic threshold. Exercising in the anaerobic zone is known as lactate threshold training, and when done correctly is thought to lead to a higher lactate tolerance ability.

The buildup of lactate is felt as muscle burn and muscle fatigue. For an endurance athlete, if you can increase your lactate threshold, it means your endurance will improve and you'll be able to fight fatigue better.

This intensity zone improves VO2 maximum (the highest amount of oxygen one can consume during exercise). This leads to an improved heart/lung cardiorespiratory system.

Interval and Tempo Training in the Anaerobic Zone

The anaerobic zone is usually reached through high-intensity exercise such as running, cycling or swimming at high speed. It is difficult to reach this zone through walking alone, although racewalkers can achieve it. This can be done in interval training with bursts of high intensity alternating with less intense activity, such as with walk/run intervals.

Threshold workouts come in two varieties, either a steady state workout at high heart rate throughout or intervals of higher and lower effort. The first is a tempo workout, where after a warmup you increase your speed until you are above 80% of the maximum of heart rate and stay at that level for 20 minutes or more before a cool down.

The second type of threshold workout has shorter intervals in the anaerobic zone. One such workout would be to first warm up, then speed up to the anaerobic zone for eight minutes, slow back to an easy pace for a minute, speed back up to the anaerobic zone, and repeat three to four times.

Anaerobic Exercise

Fast twitch muscle fibers rely on anaerobic energy systems. In strength training, jumping and sprinting these muscles are used. The bursts of muscle activity are not long enough to raise the heart rate but they use the muscles' anaerobic energy systems.

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