What is a good definition for anaerobic threshold that I can use for members and clients? Also, is anaerobic threshold activity specific? Is my AT different for swimming, cycling, running, climbing, etc?
A simple way of thinking about this is: when exercising, regardless of the chosen activity (i.e., lifting weights, running, biking, etc.), the body has three primary energy systems it uses to generate adequate energy via ATP. These are:
- Oxidative system - an aerobic process (i.e., one that requires oxygen)
- Glycolysis - there are two types: fast and slow glycolysis
- Phosphagen system - an anaerobic process (i.e., one that occurs WITHOUT oxygen)
As exercise intensity increases, the body works its way from the oxidative system to the phosphagen system. The rate at which this happens is dependent upon the rate of increase of the exercise intensity as well as factors such as nutritional status, sex, age, genetics and current level of conditioning.
So here's your simple definition:
Anaerobic Threshold (AT): The point at which there is no longer adequate oxygen for the mitochondria of the working cell(s) to produce ATP energy (i.e., aerobic energy production has failed), and thus, the cell(s) goes into anaerobic energy production (i.e., fast/slow glycolysis and phosphagen systems) for that needed energy. This has also been labeled the "lactate threshold" as this is also the point at which lactic acid begins to accumulate within the muscle, eventually inhibiting normal contractile ability.
To answer your second question, yes, AT is absolutely activity specific, just as strength training must be activity/sport specific to elicit the desired training effect. A great example of this would be to take US Olympic gold medalist swimmer Michael Phelps and place him on a bike against six time Tour De France champion Lance Armstrong. They are both extremely well conditioned endurance athletes. However, Phelps would get embarrassed because he hadn't trained his body on a bike. Vice versa would be true as well.
Thanks for the great question.