There are two thresholds used to describe the effects of exercise intensity on the body of an athlete; these are known as the anaerobic or lactate threshold and functional threshold power. The lactate threshold is difficult to detect consciously as it refers to specific metabolic changes, although it can be determined with accuracy using specialized tests. Functional threshold power, however, can actually be physically felt by an athlete during training.
What is the Lactate Threshold?
The lactate threshold is named for a substance found in the blood during any physical activity, lactate. This lactate is produced when the body burns fat and carbohydrates for energy. As the intensity of training increases, the quantity of lactate in the blood rises. Lactate is not a waste product and does not cause fatigue, as is often believed, but is used by cells and organs in the body for energy.
Lactate behavior is used to determine exercise intensity and stress on the body at different work rates. One of these points is the lactate threshold, which is defined as the point at which the level of lactate in blood rises by 1 mmol/L over exercise baseline, explains Phys Farm. Although the lactate threshold is frequently used to determine exercise intensity, this is mainly because it is an inexpensive and relatively easy method even though, in fact, it only provides athletes with an indirect marker of intensity.
When athletes exceed their lactate threshold, they begin burning more carbohydrates and utilizing the less efficient muscle fibers that use more glycogen and carbohydrates but less fat. The problem with training above the lactate threshold is that lactate stores are limited and alone are not sufficient for endurance races such as triathlons.
What is Functional Threshold Power?
Critical power is defined as the highest average power an athlete can maintain for a particular period of time, although it is often wrongly expressed as the hardest an athlete can train in a set period. The 60-minute value for critical power is typically one's functional training power.
When an athlete remains below functional threshold power, the body is able to maintain a physiological steady state. Oxygen use and lactate concentrations become level, and the concentration of creatine phosphate (PCr), ATP, inorganic phosphate and hydrogen ion (pH) in the muscles stabilize.
Once functional threshold power is exceeded, the body experiences metabolic turbulence. Although the work rate is not changing, there is a progressive decrease in ATP, PCr and pH in the muscle, explains Phys Farm. Eventually, the athlete reaches a limiting level of these markers and experiences fatigue. Exercise must be reduced to a lower intensity or ceased entirely.
Which of the Two Thresholds is More Beneficial for Athletes?
Given the evidence above, many experts regard the lactate threshold as far less important than functional threshold power. Phys Farm goes as far as to say lactate threshold is entirely unnecessary and is only used because it is easy to measure. Another way of putting it might be to say that the lactate threshold is an indirect marker of the more important metabolic adaptations that are hard to measure without expensive equipment.
In contrast, functional threshold power can be felt by the athlete. It is important for athletes to be aware of this threshold in order to avoid crossing it for a long duration if they want to achieve the best possible performance.