Lactic Acid: Good or Bad?
When the cyclist exceeds anaerobic threshold intensities, the majority of the lactic acid produced in the muscles comes from fast-twitch fibers (also called Type-II).
Together with fast-twitch oxidative fibers (Type II-A), they are utilized when the power required by the effort is very high, being able to provide the needed energy through the anaerobic lactacid metabolism, allowing the rider to sprint or progress up to higher speeds.
Lactic acid keeps accumulating, increasing the concentration in muscles and blood, until the athlete is forced to slow down.
What happens to the produced lactic acid?
To think of lactate as a useless source of problems for the athlete is a common mistake.
Indeed, the lactate molecule still contains a considerable amount of energy that can be reutilized.
A well-trained cyclist is in fact able to “recycle” the produced lactic acid: his slow-twitch fibers (or Type-I) contain elevated concentrations of H-LDH enzymes, which transform lactate molecules into pyruvate to be metabolized aerobically, thus producing energy.
Therefore whenever a cyclist slows the pace down between a series of high-intensity progressions, for example during a descent after a climb, his Type-I fibers are able to get rid of and reutilize the lactic acid coming from Type-II fibers.
The best cyclists have a particularly efficient “recycle” mechanism: it is the ability to recover in between and repeat a series of intense and prolonged efforts.
The most recommended training intensities in order to improve H-LDH enzyme concentrations in Type-I fibers fluctuate between a lactate production of 3 to 5 mM/L (higher Medio and Soglia Intensities)
An even more efficient solution is to alternate small distances (or some minutes) done at a pace slightly higher than the anaerobic threshold (4-6 mM/L) with distances done at medium tempo (2-3 mM/L): this way slow-twitch fibers get more easily accustomed to utilize lactic acid produced by fast-twitch fibers during higher intensity efforts.