Lactic Acid - Friend or Foe: Why Test For It?

An Interview with Robert Forster P.T.

Q: There has been a lot written about Lactic Acid and its role in exercise physiology and endurance cycling. What is the importance to the cyclist?

RFPT: Lactic Acid is a natural occurring by product of the Anaerobic Metabolism of carbohydrates.  That means at higher intensity exercise when your muscles are working so hard they outpace your body’s ability to deliver oxygen and are forced to use precious carbohydrates to produce energy with the by product of lactic acid.

Q: So is this a bad thing?

RFPT: No, not at first because the muscle cell can "clear" the lactic acid into the blood stream where it is swept away and a certain amount of it is “buffered” by neutralizing chemicals in the cell.  However, as exercise at this intensity continues and lactic acid begins to accumulate in the muscle cell, fatigue is quick to follow.  The other detrimental aspect of Anaerobic energy production is it uses carbohydrates as a fuel, which is in limited supply in the body.  Once it’s gone, you’re done for the day – BONKED. 

Q: Well how can a cyclist avoid this scenario?

RFPT: Modern exercise science in the study of Aerobic and Anaerobic muscle physiology identifies a clear path to improved performance.  What coaches like Chris Carmichael and Joe Friel have known and exploited so well is that training should first maximize Aerobic energy production so as to increase its contribution to the overall energy requirements of the event.  Aerobic metabolism is more efficient using fats as energy fuel and produces no lactic acid while sparing the precious carbohydrate stores.  Fat in an abundant fuel source that is virtually limitless, even in the thinnest athlete and it produces more energy per unit than carbohydrates.  Furthermore, Aerobic energy production can improve up to 12-14% with accurate training, whereas Anaerobic improvements through intervals and higher intensity exercise are only on the order of 2-6%.  Clearly, your training time is better spent developing Aerobic function.

Q: How does one improve Aerobic function?

RFPT: Sometimes called “Base Training,” Aerobic development comes from extended periods of low intensity exercise where the continuous demand for oxygen creates vascular and cellular adaptations to meet the energy needs of exercising muscle.  Higher intensity exercise simply shifts muscle metabolism to Anaerobic energy production and relieves the demand for oxygen, and therefore does not stimulate the adaptations (growth) of the systems which aide Aerobic function.  This training is when you want to avoid lactic acid production.

Q: How low is low intensity exercise?

RFPT:  The only way to know for sure is to perform a blood lactate test to actually see what is going on in the body while you are exercising.  Determining the lactate threshold, i.e. the upper limits of your Aerobic function (not to be confused with Anaerobic threshold) can only be done by this test.  Field tests, formulas and even VO2 testing does not indicate lactate threshold.  Only blood lactate testing yields the heart rate training zone or power wattage below which, your training will yield the best results in performance improvement.

Q: What are the other benefits of Aerobic development?

RFPT:  The implications of Aerobic fitness on weight management are evident.  The more you train your body to use fats as an energy source, the more fat you burn all day.  Also, Aerobic muscle function actually uses lactic acid as an energy source so when an athlete with great Aerobic fitness does work harder, the Aerobic muscle fibers actually help clear the lactic acid and stave off fatigue.  Furthermore, the vascular improvements (capillarization) will aide the delivery of oxygen and the removal of waste products so you can work harder when you need to.

Lactate Threshold:








Anaerobic Threshold:







Robert Forster, PT offers club members free evaluations and discounted services at both his physical therapy clinic and at Phase IV, Scientific Training and Performance Center.