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The Science of Performance |
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The Popular Press and Lactic Acid
If you read popular running books and/or magazines you have undoubtedly been exposed to the idea of “lactate threshold”. Basically, this belief posits that an increase in lactate levels within the muscle cells increases acidity within the muscle, resulting in fatigue. This belief in the fatigue causing nature of lactate is firmly entrenched in current training programs, with most programs including training methods to “improve the lactate threshold” or the pace that can be maintained without an excessive accumulation of lactate within the body. However, there has been an ever increasing volume of research that challenges the belief in a “lactate threshold”. The volume and quality of research that has accumulated directly contradicting the fatigue causing effect of lactate is now sufficiently strong that the exercise physiology world generally accepts there is no “lactate threshold” and that lactate does not cause fatigue. Instead, it is now believed by scientists that lactate is actually a potent and important source of fuel for the muscles. Despite the change in belief in the exercise physiology world as to the true nature and role of lactate, the belief in a “lactate threshold” continues to persist in the running community. Go to any running forum on the internet today and you will routinely see discussions of lactate threshold and how to improve it. I know of only 1 widely available running book – Lore of Running by Prof. Tim Noakes - that has attempted to set the record straight as to the new understanding of lactate. Though it has been in print for 20 years and is on its 4th edition, only recently has the information in the Lore of Running about the nature of lactate gained any acceptance within the running community. In fact, the first 3 editions of this book were considered by many to be heresy and only now, with the publication of the 4th edition, is the information starting to gain some credibility within the running community. Though the wheels of progress turn slow, they do turn. The newest information about lactate is slowly being published by the popular press and is gaining increased acceptance within the running community. Runners World magazine recently published an article basically agreeing that lactate does not cause fatigue and that there is no lactate threshold, though they did not go so far as to suggest a change in training terminology. Additionally, a new book – The Cutting Edge Runner by Matt Fitzgerald - has been published that discusses in some detail the latest thinking on lactate. So it seems that finally the Lore of Running is no longer the sole lay publication educating runners as to the latest research on lactate. I thought it appropriate to bring to your attention the information contained in Matt Fitzgerald’s new book, The Cutting-Edge Runner, so that you too will be brought up to date on some of the latest thinking on lactate (1). “Until recently, scientists believed that fatigue during high-intensity exercise was related to lactic acid buildup…
The latest research suggests that lactic acid buildup is a relatively weak contributor to muscle fatigue at high intensity. It now seems that a much stronger cause is a type of neuromotor fatigue, specifically, depolarization of the muscle cells resulting from a shift in the calcium-potassium balance…
Here’s the new theory: Muscle contractions are stimulated by electrical currents that flow throughout the body via minerals including sodium and potassium. Each muscle cell contraction involves a lightening-fast exchange in which potassium molecules inside the muscle cell and sodium molecules outside the muscle cell switch places. These exchanges are most efficient when there is a high degree of polarization (a difference in the strength of the electrical charge) between the spaces inside and outside the cells. At the beginning of high-intensity exercise, the inside of the muscle cell has a much stronger positive charge than the area outside the muscle cell. This difference in charge strength makes it easy for sodium and potassium to cross the cell membrane. During sustained high-intensity activity, potassium is released from the muscle cells faster than it can be taken up outside the muscle cells causes a progressive lessening of the difference in charge strength between the intracellular and intercellular spaces, hence weaker and less efficient muscle contractions (i.e. fatigue)…
Training leads to several adaptations that enhance a runner’s resistance to muscle cell depolarization. One of them is an increase in slow-twitch muscle fiber characteristics. Fast-twitch muscle fibers are more susceptible to depolarization. Training also increases potassium storage within muscle cells and the density and efficiency of the so-called calcium-potassium pumps that are responsible for those lightening-fast calcium-potassium exchanges.
An interesting wrinkle is that muscle cell depolarization almost always occurs at the same time as muscular acidosis (lactic acid buildup) even though the mechanisms are distinct. This is what led scientists to believe for so long that acidosis was a major cause of fatigue…
However, it is now understood that this is mostly a coincidence. It’s not the low lactic acid levels themselves but the corresponding low levels of intercellular potassium buildup that matter. Nevertheless, since it’s not possible to measure potassium buildup in humans during exercise, and since lactic acid buildup and potassium correspond so closely, blood lactate measurements will probably continue to be used to assess aerobic strength and performance potential.” This obviously raises the question as to the efficiency of “lactate threshold” training. Is training designed to improve the “lactate threshold” the most effective at also causing adaptations contributing to an improved ability to maintain the calcium-potassium exchange? Is some other training intensity or method a better method to cause positive adaptations in the calcium-potassium exchange system and hence result in greater performance adaptations? Only time, research, and experimentation will eventually tell us if “lactate threshold” training is the best training method for causing the calcium-potassium exchange adaptations now suggested as a major source of improvement or if other methods will prove to be better. In the meantime, you are now aware that lactate is not the demon it has long been believed to be. Reference: 1. Fitzgerald, M., The Cutting-Edge Runner, Rodale, 2005, pg 10-12
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