Comments from Sandra Zurcher, an orienteer who grew up in the U.S. now living in Switzerland (posted on Attackpoint, May 16, 2006).

I always feel really hesitant to write something like this, because the subject is complex and debated, so my answer can be disputed…

From what I learned in college the article has some truth, but also makes some mistakes.

Basically, lactic acid is produced when glucose in the absence of oxygen is used for energy. This lactic acid can be reabsorbed by other muscle fibers (usually muscle fibers that are not being used) and the heart muscle, and used for energy. In this sense, lactic acid is NOT all bad, and can be a contributor to the energy used for a given intensity. This means that if the intensity of exercise is at a level where lactic acid is being produced, but the body can break it down (by expelling metabolic CO2) and use it for energy in other muscle fibers, there is no build up of lactic acid in the blood, and performance is not compromised. This is known as the lactate threshold.

On a side note, metabolic CO2 is produced through the buffering of lactic acid is than expelled through our exhalation; this is the reason breathing frequency and volume of ventilation increases with intensity, in order to expel metabolic CO2 and keep a ph balance in our blood.

Where the article over exaggerates a little is in the concept of the lactic acid not being a negative factor to performance. The actual occurrences of when lactic acid is produced at a rate higher than it can be either a. used in other muscle fibers or b. expelled through our exhalation does becoming a limiting factor to performance. At intensities which are over the lactate threshold, lactic acid does decrease the muscle ability to contract and continue working at the given intensity.

This is why two types of intervals are important. First, intervals *at or just below* the lactate threshold teaches your body to use the lactic acid that is being produced and stay in a ph balance. This is the type of intervals that build endurance, stamina, it is basically a rehearsal for the speed at which competitions are performed at, and are an important part of a training routine. These types of intervals are longer in duration (2 min +) and have shorter recovery time than the interval time itself. The total volume of intervals can range up to 20-30 minutes depending on fitness levels. This is also a speed and intensity that does not (necessarily*) increase the risk of injury, and should be a pace that can be held up to 30-40 minutes.

The other types of intervals are *above* the lactate threshold. These types of intervals are what makes it possible to increase the speed of your lactate threshold. But have a bigger impact on the body, and increase the risk of injury. This is why it is very important to build first your overall endurance with long slow distance running, than work at your threshold speed in order to build the stamina needed to do intervals at intensities over the lactate threshold. These types of intervals are short in duration (no longer than 2 minutes) and recovery time is longer than the interval time. The overall volume of such intervals should be small (<10 minutes). Blood lactate levels increases during the intervals, and stay increased during the recovery. This is why they are good at training the body to buffer blood lactate. These types of intervals also stimulate fast-twitch muscle fibers, help develop neuromuscular coordination and enhance muscle recruiting patterns.

Something important to remember: if you complete intervals over the threshold, and subsequently (hopefully) your overall speed and endurance improves, this means that the speed of at your lactate threshold will also increase. This is where it gets tricky, since most people do not have access to getting a lactate threshold test, and especially not twice a year, this type of development is basically dependant on the athlete’s judgment of their progress in their fitness. Heart rate monitors are a good way to judge improvements in speed and fitness, and doing intervals on specific routes where distance can be controlled for and used for comparison also helps. Don’t forget heart rate can be altered by many different factors; caffeine, amount of sleep, stress levels, and onset of illness all have influence on your heart rate.

On a side note: The article makes the mistake to say that when the intensity is aerobic that glucose is being used for fuel, which is not really true, at an aerobic intensity the main substrate being used if fat!!

Does that answer the question? This subject is pretty complicated and there are dozens of theories about the best way to train, the best intervals to do, and why. Doug Mahoney could answer this much better. Doug if you read attackpoint please correct and improve my answer.


*please take what I am writing not as the absolute truth, and always listen to your body! Take what I wrote with a grain of salt.