The Ultimate Guide to Lactic Acid: Muscle Performance, Lactate Threshold and Sports Nutrition
Ask ten athletes about lactic acid, and you'll hear the same story: it floods your muscles, makes them burn, lingers for days and causes soreness. Almost all of that is wrong.
Your body barely makes lactic acid at all. It makes lactate, and lactate is a fuel. It doesn't cause next-day soreness, and it clears from your blood within about an hour of finishing. The goal of training isn't to produce less of it. It's to clear and reuse more of it at higher intensities.
This guide will take the guesswork out of your training and unpack the science of lactic acid, separating endurance facts from gym fiction.
WHAT IS LACTIC ACID?
Lactic acid is produced during glycolysis, when your body breaks down carbohydrate to make ATP. At your body's pH, it immediately gives up a hydrogen ion and becomes lactate.
That distinction matters for one reason: it separates the lactate molecule from the hydrogen ions. The hydrogen ions, not the lactate, are associated with the burn you feel.
| Lactic acid vs lactate | Lactic acid | Lactate |
| Found in the body? | Barely; it dissociates instantly | Yes, this is what blood tests measure |
| Role | Largely a textbook term | Fuel, signalling molecule, metabolic intermediate |
| Causes the burn? | No | No |
WHAT DOES LACTIC ACID DO TO YOUR MUSCLES?
Lactic acid fuels your muscles. Lactate produced in fast-twitch fibres is shuttled into neighbouring slow-twitch fibres, into mitochondria, and out into the bloodstream, where the heart, brain and liver take it up and burn it. Tracer research shows the heart and brain actually prefer lactate to glucose when it's available. This is the lactate shuttle, introduced by Dr George Brooks at UC Berkeley in 1986, and it overturned sixty years of thinking.
It signals adaptation. Lactate influences the expression of hundreds of genes involved in muscular adaptation and stimulates mitochondrial biogenesis, the building of new mitochondria. Producing lactate isn't a training failure. It's part of the stimulus.
It coincides with the burn but doesn't cause it. That sensation is linked to hydrogen ion accumulation and other metabolic changes during high energy turnover. It fades within minutes after you ease off.
DOES LACTIC ACID CAUSE MUSCLE SORENESS?
In short, no, lactic acid doesn’t cause muscle soreness, and the timeline settles it. Blood lactate returns to baseline within 30 to 60 minutes after you stop. DOMS doesn't start until around 24 hours later and peaks at 24 to 72 hours. By the time you're stiff on the stairs, the lactate has been gone for a day.
Soreness comes from microscopic damage to muscle and connective tissue, driven especially by eccentric work such as downhill running or the lowering phase of a lift, plus the inflammation that follows.
What this means: flushing out lactic acid two days later is chasing something that isn't there. Sensible progression, sleep, and adequate protein are what actually help.
WHAT IS LACTATE THRESHOLD?
You're always producing and clearing lactate. Your lactate threshold is the intensity where production outruns clearance and blood lactate starts climbing steeply. Roughly, it's the hardest effort you can hold for about an hour.
VO2 max sets your ceiling. Lactate threshold determines how much of that ceiling you can actually use, making it a better predictor of endurance performance. Threshold sits near 60% of VO2 max in untrained people, 65 to 80% in trained recreational athletes, and 85 to 95% in elites. Two runners with identical VO2 max can finish minutes apart on that number alone.
It's also highly trainable, which VO2 max largely isn't.
Testing it
The practical option is a 20-minute time trial. Warm up, then go as hard as you can sustain for 20 minutes. Heart Rate (LTHR): Take your average heart rate for the entire 20-minute test. Multiply that number by 0.95 (95%) to estimate your lactate threshold heart rate. For example, if your average heart rate was 170 bpm, your threshold is about 162 bpm, a solid estimate of your lactate threshold heart rate. Retest every 8 to 12 weeks.
HOW TO IMPROVE YOUR LACTATE THRESHOLD
- Build the aerobic base. This is most of the answer. Easy volume improves fat oxidation and mitochondrial density, lowering lactate production at any given pace. Successful models put 75 to 80% of training time at genuinely easy intensity. If your easy runs are actually moderate, fix that first.
- Tempo work. Sustained efforts of 20 to 40 minutes just below threshold.
- Cruise intervals. 2 x 20 minutes at threshold, or 3 to 4 x 10 minutes. Breaking it up lets you accumulate more quality time.
- Over-unders. Alternating just above and just below threshold, for example, 3 x (2 min over, 3 min under). Trains clearance while you're still working and mirrors real racing.
- VO2 max intervals, sparingly. 5 x 5 minutes above threshold, once a week at most.
- Strength training. Better economy means less metabolic cost at the same pace. Two short sessions weekly.
- Consistency. Early changes appear within 3 to 4 weeks, meaningful gains by 8, with continued improvement over 6 to 12 weeks.
Fuelling the system
Lactate is made from carbohydrate, and you cannot hold threshold intensity on an empty tank. Muscle and liver glycogen are finite, and when they run low, pace collapses.
Intake during exercise:
- Under 60 minutes: generally none needed if you started fuelled
- 1 to 2 hours: 30 to 60g per hour
- 2+ hours: 60 to 90g per hou
- Ultra distance or well trained: 90g+ per hour with gut training
The 90g ceiling exists because a single carbohydrate source saturates its intestinal transporter around 60g per hour. Combining glucose and fructose recruits a second pathway and lifts absorption to roughly 90g.
Making the maths simple
The real barrier isn't willpower; it's arithmetic mid-effort. The OTE range is built on 20g modules so you don't have to do sums on the bike:
| OTE product | Carbohydrate |
| Energy Gel | 20g |
| Energy Drink (500ml) | 40g |
| Duo Bar | 40g (2 x 20g halves) |
| Super Gel | 40g |
| Super Carbs Drink (500ml) | 80g |
60g/h is a drink and a gel, or a bar and a gel. 90g/h is a Super Carbs bottle plus a gel.
Super Carbs is formulated so that when it meets stomach acid, it forms a gel, allowing 80g of carbohydrate in one 500ml bottle to be transported efficiently for absorption. Useful when intensity is high, when it's cold, and you're drinking less, or when feeding windows are scarce. For steady endurance days, standard Energy Drink plus a Duo Bar is the more comfortable choice.
