Aerobic Threshold

James descending Isis Temple, Grand Canyon National Park. Photo: Mike Lowe
James 12 hours into an 18 hour day on a successful summit of Isis Temple, Grand Canyon National Park. Photo: Mike Lowe

What is The Aerobic Threshold?

As an endurance athlete, aerobic threshold is the most important concept to understand. The definition in a sports science lab is where the level of lactate in the blood first starts to rise over resting levels of 2 mmol/l (millimole per liter). In practical endurance terms, it is the intensity of exercise where the body starts to produce more lactate than it can process. This is the tipping point between a pace that can be maintained all day and one that can only be maintained for a shorter amount of time. A well trained endurance athlete can usually maintain a pace above the threshold for 1-2 hours. The faster the pace, the shorter the amount of time the pace can be maintained.

Why Is the Aerobic Threshold Important?

The most important reason to know your aerobic threshold is that it is the upper limit of your all day pace. This is an intensity you can maintain for hour after hour and is even more critical on multi-day efforts. At this intensity, the body is able to provide enough oxygen to process the lactate that is being produced. The aerobic threshold is also the upper limit of energy production for movement where fat oxidation is the predominant energy source. At this intensity, the body is using a mixture of 50% fat and 50% carbohydrates to fuel movement.

Raising your Aerobic Threshold

Raising your aerobic threshold is the most important factor in improving performance in long endurance activities. Higher aerobic threshold means a greater aerobic capacity (the ability to perform low to moderate exercise for long periods of time). High volume training at or below the aerobic threshold will slowly raise the threshold over time. This allows an athlete to train at a higher intensity (faster pace, steeper grade, heavier pack) and sustain it for multiple hours. Even elite athletes spend at least 80% of their annual training time training below the aerobic threshold.