If you pick up any health or fitness magazine or listen to any sporting event broadcast you’re likely to hear some reference to how lactic acid causes fatigue, burning muscles, muscle stiffness or cramping, injuries, increased blood acidity, torrential rainstorms, and animal cruelty. The reality is that none of these are true. The myth that lactic acid is the root of all evil is based on a flawed conclusion from a single scientific study over a century ago by Otto Meyerhof. The fact is, lactic acid almost doesn’t exist in the human body. Lactic acid is created as a metabolic byproduct of the anaerobic glycolytic energy system (the same one responsible for supplying the body with much of its energy for relatively high intensity, moderate duration activities of 20-90 seconds) but the majority (95+%) of it is almost completely dissociated to lactate and hydrogen ions. Well AHA! you may be saying….it’s the lactate that’s causing all these problems. Again, this is another myth perpetuated by the main stream media. The increased concentration of lactate doesn’t increase acidosis in the muscle, directly cause fatigue, and is not responsible for delayed onset muscle soreness. In fact, the body can deal with the lactate relatively efficiently and even use it to its benefit as a form of fuel via two lesser known energy systems. Lactate can be converted to glucose in the liver (via the Cori cycle) and released back to the body for use as an energy source or it can be oxidized to pyruvate which will be used to power the Krebs cycle. While that may have little relevancy to you as a coach, the take home point is that LACTATE PRODUCTION CAN ACTUALLY HELP PRODUCE MORE ENERGY via its conversion to glucose.
So if we’ve cleared lactic acid and lactate from any wrong doing, what’s the source of the fatigue and burning muscles? It’s largely considered (although not a concensus) to be from acidosis as a result of the Hydrogen ions or some other inorganic phosphate. And while it may seem like a logical step to conclude that more lactic acid production (and thus lactate) as a result of intense activity will increase the production of hydrogen ions this isn’t quite so simple. Hydrogen ions will only accumulate if lactate doesn’t consume them, because the lactate can actually allow their transport from the cell….ensuring that Hydrogen ion accumulation via increased lactic acid production doesn’t get out of control. So although Hydrogen ions are considered to be the main villain in this story, it may not be in direct (or indirect) relation to lactic acid (or lactate) production. That said, many researchers still consider increased lactate concentration, a good indirect indicator of fatigue due to cellular acidosis despite not being the cause of it.
So what are the implications for training? It won’t directly affect the types of workouts you’ll do for a long sprinter or middle distance runner. Many of the guidelines used for years about duration and intensity of runs will still apply. What it does mean is that we can re-examine post-workout recovery periods and what we can and should do after the workout to assist in using lactate for fuel. It also gives you information for figuring out what is making your athletes sore (because it’s not lactic acid / lactate and might be something completely different) which has important implications for periods of the year when soreness should be minimized.