A post shared by Michael Tromello (@mtromello)
Let's start with the simple things first, lactic acid build up and the lactate threshold are not the same thing. The real term for what is euphemistically called lactic acid build up, what's supposed to make it hard to push through an intense workout becuase of "the burn," is lactic acidosis.
Lactic acid is always produced in some quantity, along with another intermediate by-product called pyruvate, in the long sequence of reactions that take place in the breakdown of glucose during exercise.
If you are not working out too intensely the lactic acid will break down and get released as energy in the presence of oxygen. If you work out really intensely, you body looks to use more glycogen for fuel because it can get a hold of it quickly but you then get a build of lactic acid, you breathe heavier to get more air to oxidize the pyruvate.
At some point, you can't get enough oxygen in to meet the demand and lactic acid builds up, which is when you can get the proverbial burn as the concentration of acid ions goes up.
The rise in intensity of activity correlates to a rise in blood lactate levels and the lactate threshold is the point at which you move from the efficient oxygen in, burning fuel, aerobic capacity for work to the gulping for air, change in energy creation, air be damned just keep me going anaerobic capacity part of your workout.
In general terms, the concentration point for blood lactate of 4 mmol/L is used as a threshold transition point, the point at which it becomes difficult to maintain a steady heart rate and amount of power output.
As Coach Mike Tromello says in his Instagram post above, CrossFit athletes need to be training their lactic acid to achieve peak performance, too. Runners need to work on their threshold in a single domain whereas CrossFit athletes need to work across multiple domains, maybe within the same workout.
All that just means that an athlete, or just someone looking to get better performance, be fitter in their activity, has to push that threshold point out so that their steady state of activity – the point at which they are solidly moving along and maintain a healthy level of activity consistently – is occurring at higher intensities.
You can see how that makes sense in endurance events like running; you want to maintain the fastest consistent pace over time to get the best times.
Same with CrossFit, you want to be able to maintain high workloads at higher intensities while getting the energy your muscles need in the most optimal manner possible.
Don't Forget Your VO2max Capacity
As an aside, it's worth noting that to get a feel for how tolerant we are of consistent hard work we need to look at two measures. One is your lactate threshold and the other one is your VO2max number. The VO2max equates to the maximum amount of oxygen consumed by someone working at maximum intensity.
In simple terms, the more oxygen you consume, the greater your capacity for intensity and the greater the workload you can handle in a workout because, like we said, you need oxygen to burn fuel for your muscles efficiently and as intensity increases you need more of it.
Therefore, athletes with higher VO2max capacity are likely to run, swim, or bike longer and faster because they can use more oxygen more efficiently.
Monitoring Intensity with the Talk Test
All this stuff a massive oversimplification of energy systems and the glycolytic system but carrying a chemistry book and lab kit into the gym seems a bit pretentious. And, you can't accurately get your VO2max or lactic threshold without invasive testing under controlled conditions.
It makes a lot of sense to let yourself be used as a lab rat if your whole life and career depends on improving your performance, like going for gold at the Olympics, but it's not remotely necessary even for the one percenters in the gym. You can train your lactate threshold by self-monitoring with two measurements: heart rate and your breathing.
Heart rate is easy enough and there are a plenty of affordable gadgets and devices you can get to help you track that across the most grueling and varied of workouts.
Breathing is even simpler and it is the talk test. It starts with the ventilatory threshold, that's the point at which you start gulping for air, your breathing drastically changes. Bad news is you are suffering but good news because it typically occurs shortly after the lactate threshold has been reached and it is an obvious marker that shows increased intensity.
The talk test is an effective way to measure yourself in exercise programs because, as you may have heard in many training instructions, you want to maintain a pace where you can still talk, even if it is a little labored.
Beginners always benefit from that advice as they built up their capacities and their endurance. More seasoned athletes can use the talk test to mark how far they have pushed that lactic threshold by comparing to previous points in their workouts.
It may seem counterintuitive, especially at the top tiers of athletic performance, but you don't want to be straining with effort. In effect, you don't want to burn out and be unable to give sustained effort.
You can watch great athletes, even in moments of great stress and fatigue, they don't strain but continue to maintain the highest levels of performance that they can manage.
They have the capacity to keep burning bright in the game, but that doesn't mean they don't collapse at the end when they're at the finish line. For the average trainee, being able to do an Energizer Bunny thing is a sign of how efficiently you are managing your workload.
Learning to train the lactate threshold is a great way of raising your game. And it's as simple as listening to yourself talk.
The references to research papers below are pretty good places to get a read on all that I have written about here. You can go as deep as you like, or not, as the case may be.
I like to think that the more complicated you try and make your training, the harder it is to make progress, that's why I stick with the talk test.
At the end of the day, you need to listen to your body, recognize its signals, and be able to push out the breakpoints in your endurance over time. If you're just beginning, think of it this way: you take a flight of stairs quickly, and you're gasping for air at the top.
You train for a few weeks and the next time you take the same flight of stairs, you get to the top and your breathing seems pretty normal, you can talk and you move on.
Now keep adding stairs, and keep getting to the top able to carry on a conversation. That's progress.
De Lucca, L., de Oliveira, F. R., Foster, C., & Carminatti, L. J. (2021). Talk test: A simple alternative to identify lactate thresholds during progressive cycling exercise. Kinesiology, 53(1), 20–27. 
Fell, J. W. (2008). The modified D-max is a valid lactate threshold measurement in veteran cyclists. Journal of Science and Medicine in Sport, 11(5), 460–463. 
Hogg, J. S., Hopker, J. G., & Mauger, A. R. (2015). The self-paced VO2max test to assess maximal oxygen uptake in highly trained runners. International Journal of Sports Physiology and Performance, 10(2), 172–177. 
Moreno-Cabañas, A., Ortega, J. F., Morales-Palomo, F., Ramirez-Jimenez, M., & Mora-Rodriguez, R. (2020). Importance of a verification test to accurately assess V?O2max in unfit individuals with obesity. Scandinavian Journal of Medicine & Science in Sports, 30(3), 583–590. 
Quinn, T. J., & Coons, B. A. (2011). The talk test and its relationship with the ventilatory and lactate thresholds. Journal of Sports Sciences, 29(11), 1175–1182.