There are several terms in training articles that get thrown around in confusing ways: aerobic threshold, lactate threshold, anaerobic threshold, aerobic capacity, VO2 Max, anaerobic capacity, and functional threshold power or pace. Many of these terms have definitions that are quite similar to each other, with minute differences that matter in the field of sports science, but are basically equivalent for athletes training. These terms all fit into three main categories that are important for us to understand as endurance athletes.

Aerobic threshold (AeT)

The aerobic threshold is defined as the intensity of exercise at which lactate levels in the blood begin to rise from their baseline. Lactate accumulation indicates that the metabolic pathways that are fueling our muscles with energy have begun to shift to a combination of aerobic and anaerobic mechanisms, and if the intensity that we are working at stays the same, or increases, lactate will continue to build. This is in effect an endurance limiter. Aerobic capacity is essentially the same term – it refers to the amount of work that can be performed before the athlete reaches their AeT.

Lactate Threshold (LT)

Lactate Threshold is the level of intensity at which lactate in the blood reaches 4 millimoles/liter. This is a tiny amount and is something that requires a blood test during exercise in a lab to determine. The more useful definition for athletes is that it is the intensity at which lactate production exceeds its removal. This is also the defining line above which, exercise can only be sustained at that intensity for short periods of time before fatigue and slowing set in. Consider this the upper-end limit to endurance. While the definitions are slightly different, this is essentially the same thing as Anaerobic Threshold (AnT) anaerobic capacity, and functional threshold. They all refer to the point at which the metabolic pathways switch to a primarily anaerobic pathway that burns glycogen (carbohydrates), and the ability to sustain that intensity will be limited.

VO2 Max

VO2 Max refers to the maximum amount of oxygen that the body can utilize for energy during an all-out effort that is well above their AnT. Theoretically, the better your body is at delivering oxygen to where it needs to go, and the better adapted your muscle cells are to exercise, the more oxygen they will be able to utilize to make ATP (energy) and the more energy they will have to do work. Sounds simple enough right? VO2 Max has been a big focus in endurance sports for a long time, partly because it is easily quantifiable. However, ask elite coaches, such as those at Uphill Athlete, and they will tell you that VO2 Max doesn’t correlate very well to performance, and seems largely determined by genetics. Athletes for decades spent considerable effort training to increase their VO2 max, but recent studies suggest that that time would be better spent increasing the aerobic threshold.

Why do these terms matter? One dispels a popular myth related to training (VO2 Max), while the other two are the categories where we as athletes have the greatest abilities to affect our metabolic and motor pathways to achieve better performance. The balance of aerobic threshold and lactate threshold training that we do as we prepare for a large climb will determine how we perform. We’ll be diving into these two topics in more depth in the coming weeks so stay tuned!

_____

There are several great resources that provide a lot more information on these topics. For this article, we pulled from Joe Friel’s blog and from the recent book, Training for the Uphill Athlete, from the folks at Uphill Athlete. We can’t recommend the book enough if you are serious about training for endurance mountain sports!

Comments? Questions? Share your thoughts here in the comments!