Lactate Kinetics and How to Make a S’more

Lactate, lactate, lactate. Nowadays it seems everyone’s training is all about measuring blood lactate. While many preach its importance, how many people know what lactate is or the enzymatic processes involved? I certainly believe measuring lactate is valuable, but I also believe understanding the fundamental processes make it even more so. I hope you enjoy reading (as much as I did writing) my first physiology post since 2020; Lactate Kinetics and How to Make a S’more.

Let’s simplify this to something more enjoyable yet still involving sugar, making a s’more (noun: a delicious snack that brings joy to every recipient). If you don’t know how to make a s’more then I recommend investing more time in trying to live a little instead of learning about lactate kinetics (the study involving rates of reactions and how they are affected). Ah, the sweet simplicity of skewering a fresh marshmallow and setting it ablaze over the fire, then using your burning ball of goodness to melt some chocolate before mating them together between some crisp graham (#carbwithcontext) is one of the peak pleasures of life. BUT have you ever been around a campfire and the skewer to human ratio is too low? Or the fire is closer to a slow cooker requiring 5 minutes per marsh? So you just start ripping bags open and eating raw marshmallows to satiate your hunger all while leaving your sticky marshmallow finger residue everywhere you go? Well then perhaps you also know the feeling of failing muscles in a race or workout after going out too fast because “it just felt so good (until it didn’t)”. I am quite experienced in both, and I assure you that they're not as different as you might think. 

In this crude yet simple analogy, it is proper roasting of a marshmallow yielding a scrumptious s’more that is the slow potential-maximizing equivalent of aerobic respiration (energy production WITH O2). The number of skewers available is the concentration of rate limiting enzymes (enzymes that determine the overall speed of a reaction) of aerobic respiration, while the temperature of the fire can be associated to the transport rate of oxygen, the critical part of aerobic energy production. Glycolysis, is the breakdown of glucose to pyruvate. This process produces energy and does not require oxygen. Pyruvate is what is ultimately needed for the krebs cycle, the first part of aerobic respiration, BUT glycolysis can also act independently to produce energy rapidly without oxygen (anaerobic/fermentation), yet inefficiently and it produces lactate (a similar structure converted from pyruvate, that allows glycolysis to continue upon itself). So therefore, ripping open the bag of marshmallows is PFK-1, the rate limiting enzyme of glycolysis, and the underwhelming joy of the raw marshmallows is the low efficiency/high rate energy production produced through anaerobic respiration by producing lactate.And the sticky fingers that seem to be ruining your day is the build-up of hydrogen ions [H+] as your blood pH potentially starts to drop.

If you’re still following now, then get ready as this is when things get complicated, as my crude analogies lose a bit of relevance. In my s’mores example imagine the BAG of marshmallows to be glucose or glycogen (stored glucose, tied together), and the marshmallows inside are PYRUVATE. Which is the main reactant/input to go into the Krebs cycle, the first step of aerobic respiration. However, getting pyruvate into the first step can be slow, so naturally just ripping open that bag and fisting those mallows is a more rapid yet inefficient process of anaerobic respiration through lactate production. LACTATE is a handheld marshmallow.

  Lactate gets a bad rap because it is associated with “lactic acid”, though in reality lactate + hydrogen ions is “lactic acid”, but it is the [H+] that is the real villain! This is why sodium bicarbonate/baking soda is common to combat the potential acidic drive of anaerobic respiration (stick around for a post about blood buffering in a future post perhaps). BUT lactate is not the enemy, in fact basic enzyme kinetics proves that a higher concentration of LACTATE increases the rate of PYRUVATE production. So back to the campfire s’mores example, imagine that as soon as your pal Mitochondria Mikey is done roasting his marshmallow and plops it on a fresh graham and bar, he can then go and open a bag and stick a bagged marshmallow onto his skewer (pyruvate from glucose), OR you use Lactate Larry duel-wielding marshmallows immediately able to load those suckers onto the skewer and back it goes into the fire with Mclaren level pit stop speed (pyruvate from lactate).

  So, the maximal rate of S’MORE production (or Aerobic respiration) is a function of the number of available skewers, the fire temp, AND how fast one can rip open that bag of marshmallows and reload the skewers despite sticky hands. BUT you also don’t want 20 Lactate Larry’s running around with lactate marshmallows and sticky fingers! No, you want a sustainable and efficient amount of pyruvate produced via lactate and glycolysis.

Why is this relevant to me? Well as a triathlete or any endurance athlete first determine where are you limited? For the glycolic monster, the speed demon, the 2 min champ, further practicing opening the bag of marshmallows isn’t going to help you if every marshmallow is just waiting for their turn around the fire that is still too cold. For them, aerobic fitness development is the key. 1. Get more skewers and 2. Grow the fire. Long steady efforts below threshold (more on that in the future too). May be boring, but s’mores are worth the wait. For the diesel athlete, the one gear grinder, the steed of stamina, maybe you get to that bag of mallows to grip it and rip it without fear of breaking a nail. High end work is best to develop anaerobic capacity. Hill sprints or 4hunids running, long interval swim sets, or high-end bike intervals well above threshold are best, all with plenty of rest to restore anaerobic capacity between intervals.

  It is very much worth mentioning that your preparation should be based on the EVENT you are prepping for as well as the type of athlete you are now. If you’re training for a full distance Ironman, it is VERY unlikely that you are glycolytically limited, therefore if you’re doing a lot of very high-end work, ask yourself “why?”. Similarly, a “sprint” triathlon is still around an hour so the amount of aerobic vs anaerobic stimulus needed should be calculated. Alternatively, the athlete stuck at the speed for a 10k to half marathon could likely benefit from more high-end work. (note: there are other benefits to high end work but this is overly simplified for the sake of understanding the fundamental principles).

So, to bring it back to the beginning! Why is everyone preaching about lactate in their training?? Because measuring blood lactate during training is the best way to see WHAT you are doing with marshmallows or HOW you are generating power! Perceived exertion is NOT a valid measure of what is “threshold” (biochemically defined as the point in which the RATE of eating raw marshmallows increases faster than the increase rate of power production. Aka when you can no longer keep up with power demands by roasting proper smores). The typical first lactate threshold (LT1) is USUALLY around 2.0mmol and second lactate threshold (LT2) around 4.0mmol. HOWEVER, this can shifted by training, and the PERCIEVED EXERTION of 4mmol maybe be challenging for some, and extremely easy for others. This is also why a 20 minute test will NEVER be able to truly measure threshold. Even multiple variable tests like ramp tests are not able to actually MEASURE lactate threshold.

  Personally, I use a lactate meter multiple times as a week just like plenty of the best programs in the world do like Norway Triathlon. This is precisely why the Mike Squad Coaching crew utilize shared team lactate meters to mail around from athlete to athlete to both test these TRUE thresholds and continue to retest during allocated weeks to revalidate these zones at various points in training. Time is everyone’s most valuable resource, so spending your time training in ways that are not intentionally developing your weaknesses are a waste of your precious time, money, and potential as an athlete.  

  I could talk/type for hours about S’mores, biochemistry, and endurance sport training. So, if you want to chat more about anything from allosteric inhibitors, like citrate, affecting the rate of PFK1 to why the Hershey’s cookies and cream bar is the goat of chocolate bars then slither on into those DMs or e-mail. Happy training yall. 👌🏻

Michael Arishita

@swimmikerun

Michael.arishita@gmail.com