The terms lactic acid training and lactate threshold training refer to the same thing: increasing your levels of physical endurance at high intensities. However, science is continually evolving, and the relationship between lactic acid and muscle soreness isn't what you may have once been told.
About Lactic Acid Training
As exercise researchers from the University of New Mexico explain, lactic acid is not, as is still commonly taught, the devil that makes your muscles burn when you work out. It's true that lactic acid — or actually, lactate — develops as a byproduct of glycolysis, an anaerobic energy pathway used to fuel your muscles during high-intensity exercise. But lactate is not the cause of the burn you feel; it's instead the remedy, forming as it takes up the accumulation of protons that actually create that burn.
Your lactate threshold is a measure of the maximum exercise intensity you can sustain without fatiguing — or, to put it another way, it's the point at which lactate accumulates more quickly than your body can remove it. Said threshold is considered a very consistent predictor of how an athlete will perform in endurance events. The higher your lactate threshold, the higher your capacity for intense, prolonged effort.
As the two common names suggest, lactate threshold training or lactic acid training — sometimes abbreviated as LT training — is meant to increase your lactate threshold and thus your capacity for high-intensity endurance efforts.
As the UNM researchers note, science's understanding of the mechanisms behind a lactic acid workout method continues to evolve — but the studies are already robust enough to provide a reliable collection of best practices. To get the best results, the ideal lactate threshold training program will combine high exercise volume, maximal-effort steady-state exercise and interval training.
Determining Your Lactate Threshold
The first step in creating a lactic acid workout program is determining the current exercise intensity at which you reach your lactate threshold. For a true determination of lactate threshold, you need a thorough fitness test in an advanced laboratory. But the American Council on Exercise presents a validated test for determining and tracking lactate threshold. Although this is ideally done with the help of a professional trainer, you could in theory carry it out on your own, with a friend nearby to take notes for you.
The test involves first warming up with five to 10 minutes of low-intensity exercise, then running or walking as fast as you can for 30 minutes on a treadmill at 1 percent grade. Your average walking/running speed through that 30 minutes is determined to be your lactate threshold in terms of speed.
You can also take your heart rate every five minutes, then calculate the average to represent your heart rate at the lactate threshold; if you do this, make sure you use a chest-strap heart rate monitor that has been clinically validated for accuracy. ACE notes that improvements in your lactate threshold will be confirmed if, over time, your running speed increases while you maintain the same or similar heart rate levels.
You can also make a rough estimate of lactate threshold using the rating of perceived exertion, or RPE, scale. The UNM researchers note that your lactate threshold typically falls between 13 and 15 on the RPE scale, which corresponds with a "somewhat hard" or "hard" level of exertion. However, it's worth noting that a small but interesting study of 32 young women, published in a 2015 issue of BMC Sports Science, Medicine and Rehabilitation, found that the lactate threshold generally corresponded to a significantly lower RPE rating for people who weren't used to distance running or race walking.
Make sure you log the results of your lactate threshold evaluations, whether you're using the validated treadmill/heart rate protocol or your RPE. You can repeat the same evaluation method at intervals to track how your lactate threshold is changing.
Lactate Threshold Workout Priorities
So how do you train to increase your lactate threshold? As already noted, the science around these methods continues to evolve. But experts readily acknowledge that a combination of light-intensity volume training, a relatively small percentage of maximal steady-state training (at your lactate threshold) and lactic-acid interval training above your lactate threshold will yield improvements in your lactate threshold.
The exact mechanism behind this is still being pinned down: Theories include the notion that some of the noteworthy adaptations that increase your lactate threshold are an increased capacity for mitochondrial respiration (your mitochondria are the "energy factories" of your cells), an improved ability for your muscles to use lactate for energy, and better circulation to clear excess lactate from your muscles.
The UNM researchers recommend beginning your lactic acid training by increasing the weekly volume (or to put it another way, the duration) of your low-intensity training sessions, working at an RPE of no more than 11 to 12.
ACE also recommends doing either steady-state workouts at your lactate threshold or high-intensity intervals that surpass your lactate threshold, aiming for 95 to 100 percent of your maximal heart rate — or RPE values of 17 to 20. (The RPE scale runs from six to 20, so 20 is considered to be an all-out, truly maximal effort that cannot be sustained for a long period.)
The council suggest starting with only a couple of interval repetitions, eventually working up to six to 10 cycles of two- to three-minute work intervals with two- to three-minute recovery intervals in between. In either case, limit yourself to no more than one high-intensity interval session or steady-state session per week. As always, allowing appropriate recovery time between your workouts is an important part of designing any exercise program.
Note that in all three training modalities, you should start with what you're capable of now and gradually increase the workout duration or intensity over time. Both ACE and the UNM recommend increasing training volume by no more than 10 to 20 percent per week. This sort of gradual increase helps guard against injury and overtraining, both of which would ultimately set back your results in lactic acid training.
- University of New Mexico: "Lactate Threshold Training"
- American Council on Exercise: "How to Design a Lactate Threshold Training Program"
- BMC Sports Science, Medicine and Rehabilitation: "Relationship Between Perceived Exertion and Blood Lactate Concentrations During Incremental Running Test in Young Females"
- American Council on Exercise: "9 Signs of Overtraining to Look Out For"