That extreme fatigue or nauseous feeling you get after performing 5 sets of 10 RM squats? Or after repeated sprints on a track or in a pool?
That’s just your dear friend Lactic Acid saying hello.
Exercise requires effort. That extra effort thus requires your muscles to receive more oxygen. Your heart rate increases, and you begin to breathe faster in order to carry that extra oxygen through the blood to working muscles so they can create the energy necessary to perform a given exercise activity. (i.e., Aerobically — “aerobic” meaning “with oxygen“)
However, some exercise activities, like high-volume squats and sprinting, are of such high intensity that they consume energy much faster than can be produced aerobically. The oxygen simply cannot be delivered to the working muscles fast enough to keep up with their energy demands. When this happens, the body switches to Plan B — producing energy for the working muscles without oxygen (i.e., anaerobically.)
The body prefers to utilize oxygen to produce energy for working muscles because it’s easier. As long as you continue breathing, oxygen is provided in endless supply, and the cycle of producing energy can continue unimpeded. When that is not an option, Plan B will suffice for sustaining high intensity exercise, but it’s less desirable and comes at a cost: a buildup of lactic acid in the activated muscle and blood.
Think of it like drinking black coffee. It doesn’t taste as good as coffee flavored with cream and sugar, but it gets the job done.
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I’m sure you’ve read about, or heard people refer to, the lactic acid “burn” during intense exercise. That is an accurate and appropriate description, given the body’s now-increased acidity level and the fact that acid does indeed “burn.”
Lactic acid does NOT cause muscle soreness. Muscle damage causes muscle soreness.
Given that lactic acid accumulation literally creates a more acidic environment in the blood, the body can only tolerate so much, so anaerobic energy production for working muscles can be sustained only temporarily. Once the lactic acid reaches a certain threshold (peak lactate levels are reached in no more than 1 to 3 minutes), the body must take measures to reduce the degree of acidity and raise pH levels back to within a normal range. (Note: On a pH scale of 1 – 14, the lower the number, the higher the acidity).
This is achieved by a forced reduction in exercise intensity. The activated muscles thus fatigue and begin to slow down. Once performance returns to a lower, more aerobic intensity, or ceases all-together, the body can begin to metabolize, or break down, all of the accumulated lactic acid in the working muscles and blood.
An easy example of this process is track and field sprinters. They are running SO fast that the body must produce energy for the working muscles without oxygen’s help. (Its delivery is too slow…If only it had Amazon Prime!) So the muscles keep performing while lactic acid builds up in the sprinters’ system, propelling them through the finish line, and drastically fatiguing the muscles. Once the race ends, and the intensity level plummets, the body can then utilize delivered oxygen and begin the process of removing all that lactic acid.
OK, but how long does THAT take?
In conjunction with the phrase “lactic acid burn”, you’ve likely also heard reference to the process of “flushing out” the lactic acid. People often comment that they’re just going to do “some light cardio” or “a light lift” the day after a high intensity workout…to “flush out the lactic acid.”
Unfortunately, those folks are misinformed about how the process works. So let me clarify simply:
Contrary to popular belief, nearly all accumulated lactic acid is removed from the blood within 1 hour and 15 minutes.
Yes, you read that correctly – in less than 90 minutes, it’s gone. Not 8 hours later. Not 48 hours later. Less than 90. Minutes. Later.
With that said, doing a light activity immediately after a high intensity workout does help remove the lactic acid more quickly. So if your day-after, light workout is done with the intent of getting rid of lactic acid buildup, don’t worry….it was gone a long time ago.
With high-intensity resistance training specifically, blood lactate levels decrease faster when performing light movement between sets than simply sitting and resting.
So the next time you decide to perform a high volume training session, like 6 sets of 10 RM back squats with two minutes rest in between sets, you’ll remove the lactic acid more quickly, and thus recover faster, if you get up and walk around or do a few body weight squats instead of just sitting down and scrolling through your Instagram.
The same can be said of repeated sprints. Instead of completely stopping between bursts, continue moving with a light jog or walk. You’ll feel far more recovered as you begin the next sprint than if you just stand around idly waiting.
In summary, lactic acid is harmless. It’s simply a side effect of exercising at high intensities. So don’t let it deter you from attempting to push yourself harder during training. Choose instead to welcome lactic acid with open arms!
