A Brief History of Lactate

Over the years, lactate has been the subject of a great deal of research, debate, and confusion.
It wasn't terribly long ago that most scientists believed that lactic acid was responsible for the
burning you feel in your muscles and was also the cause of muscle soreness. Most of this belief
initially came from the finding that at higher and higher intensities and workloads there is more
and more lactate that accumulates in the blood. In other words, the harder and longer you
work at high intensities, the more lactate you end up accumulating.
Eventually, research showed neither of these things to be true and that lactic acid as a
substance doesn't really even exist in the body in meaningful levels. Scientists were also able to
see that the lactate produced during high intensity exercise was essentially gone in under an
hour so it certainly didn't make sense that it was causing soreness that you typically felt one or
two days later. So if it wasn't lactic acid causing the fatigue or soreness, then what is?
Over the course of a great deal of research on lactate, the conventional wisdom soon became
that during the breakdown of glucose into lactate (anaerobic glycolysis seen in fig. 11) there is
also net production of hydrogen ions (FR). It is these acidic ions rather than lactate, scientists
believed, that lowers the pH of the cell and interferes with muscular contraction.
In other words, it's not the lactate or any lactic acid that causes the fatigue, but rather the
hydrogen ions that get produced at the same time and through the same chemical pathways as
the lactate. This helped explain why we see the correlation between lactate accumulation and
fatigue. This model has been the prevailing line of thought for a great many years and is taught
in most medical and physiology textbooks today.
Recently, however, this line of thought has also come under scrutiny and called into question as
well. Some scientists now argue that the hydrogen ions don't actually come from the same
reactions that produce lactate, but actually come from a completely different part of energy
production. Instead, they believe that lactate production inherently helps delay fatigue because
it "soaks up" a hydrogen ion as pyruvate is converted into lactate. In this process a molecule
known as NAD that is required for glycolysis is also freed up and donated back up the chain.
Perhaps even more interesting, there's been research in the last few years indicating the
possibility that the increased acidity in working muscles might actually play a role in preventing
fatigue rather than causing it on some level as well! The exact proposed mechanism for this has
to do with maintaining an electrochemical balance necessary for muscular contractions, but
more research in this area is necessary before too many conclusions can be drawn.
While all this chemistry may sound confusing, the main important principle to take away is that
lactate is not the bad guy it has been made out to be. Whether or not the hydrogen ions that
are part of muscle fatigue result from the same chemical pathways as lactate production or
they come from elsewhere isn't really that important. Just understand that lactate itself is not
really causing fatigue, and in many ways it is actually helping to delay it.

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