​The Myth of Lactic Acid

Almost everyone has pet peeves—little things that continue to annoy you.  As a professional coach and exercise scientist I have quite a few.  One of the most annoying is listening to coaches and other so-called “fitness experts” tell their athletes that lactic acid causes them to slow down or make their legs sore. 

It is a myth that began many years ago.  Way back in 1922 Nobel Prize winners Dr. Otto Meyerhof and Dr. Archibald Hill independently conducted research in which electric shocks were administered to severed frog legs.  Initially the frog legs would twitch before eventually becoming still.  Upon inspection, the severed frog legs were awash with lactic acid.  The scientists deduced that since the severed legs were not receiving a supply of oxygen from the original organism, then the anaerobic energy system produced “lactic acid,” which led to a condition of “acidosis.” 

It was then assumed that “acidosis” shuts down muscle fiber contraction.  Coaches and runners readily accepted this theoretical finding and then spent nearly sixty years attempting to train to overcome the effects of lactic acid. 

It wasn’t until 1985 that University of California at Berkeley physiologist Dr. George A. Brooks demonstrated that lactate is actually a valuable fuel for our muscle fibers and not the villain it was assumed to be. First, you must understand that lactate is for all practical purposes lactic acid minus a hydrogen ion. The new theory was that lactic acid splits to create both lactate and hydrogen ions; lactate is good and hydrogen ions are bad.  So lactic acid still remained somewhat of a villain to athletic endeavors.
 
Then in 2004 Dr. Robert A. Robergs and others presented another blow to the dwindling ill-famed reputation of lactic acid. In their paper they claimed that lactic acid “is never created during anaerobic energy production.” Instead, the dreaded hydrogen ions arise independently of lactate. And, lactate actually decreases acidosis in muscle tissue both by consuming hydrogen ions and by pairing with them to exit the muscle fiber with the assistance of transport proteins.
 
Dr. Laurence A. Moran, a biochemist and textbook author, celebrated Robergs’s, (and associates) findings by proclaiming, “The important point is that lactic acid is not produced in the muscles so it can’t be the source of acidosis.” 

More recent research has continued to challenge the role of acidosis as a cause of fatigue. McKenna and Hargreaves stated, “Fatigue during exercise can be viewed as a cascade of events occurring at multi-organ, multi-cellular, and multi-molecular levels.”
 
The current thinking is that lactic acid is not a villain at all. Instead lactate is a valuable energy source, which can be used to continue muscle contraction. It is formed and utilized continuously in diverse cells under both anaerobic and aerobic conditions. So, lactate itself does not cause fatigue but certain accompanying products might. The accumulation of hydrogen ions and the corresponding lowering of pH is most likely the cause of acidosis, which has a direct relationship with muscle fatigue--an inability to generate high muscle contraction forces and sometimes producing a burning sensation in affected muscles.
 
Smart coaches and athletes have adapted their training methods to increase the utilization of muscle (and blood) lactate.  Our own experience with training our post-collegiate, Olympic development athletes is that we have targeted very specific training to increase lactate utilization during both training and competition.  Our “Lactate Shuttle” sessions are a core part of our training programs.
 
We utilize “Lactate Shuttle” sessions to “buffer” the effects of hydrogen ions within the muscle fibers and enhance the movement of lactate within and between the cells.  Lactate is a fuel, not an acid, but is still closely associated with the production of hydrogen ions.  Lactate and hydrogen ions leave the muscle fibers together escorted by specialized transport proteins.  Our “Lactate Shuttle” workouts are targeted to increase these transport proteins, therefore increasing the facilitated diffusion across the cell membrane and improving lactate dynamics.
Lactate DOES NOT cause muscle soreness.  Since lactate is a fuel source, it is utilized quickly and removed from both muscle tissue and blood soon after even intense exercise bouts. It does not linger for days and is usually reduced to “normal” levels within an hour post exercise or much sooner if a cool-down session follows.
 
In summary, if your coach or trainer states that “lactic acid” is causing you to fatigue or produce sore muscles, you should be cautious, as they are uninformed and propagating a “myth.” 

Author Mike Caldwell is coach/director of ASICS GTC-ELITE and this article was written for and originally appeared in PACE Running Magazine.

---