Lactic acid: more than just metabolic waste

[01dragonslayer]

By Glenn Koslowski
Lactic acid, long blamed for muscle burn and post-workout soreness, has been misunderstood for decades. Traditionally seen as a “waste product” of anaerobic metabolism, lactate has been for decades the villain in fatigue and poor performance. But what if the science has changed? Research suggests that lactate is not just a byproduct, but a powerful fuel source and signaling molecule that can enhance endurance, recovery, and even muscle growth. It’s time to rethink lactic acid’s reputation. This isn’t just waste; it can be fuel in disguise.

Here’s a quick myth for you: for years, athletes and coaches believed that lactic acid buildup led to muscle soreness (DOMS) and performance drop-offs. But in truth:

• DOMS is caused by microscopic muscle damage, not lactate;
• Lactate levels return to baseline within 30-60 minutes post-exercise;
• Fatigue during intense activity has more to do with hydrogen ion accumulation and consequent pH drop, not lactate itself.

But that’s where things get interesting: lactate is not just tolerated; it’s actively used as fuel by the body:

• Oxidative tissues like the heart, brain, and slow-twitch muscles love lactate. They convert it back into pyruvate for use in the mitochondria;
• The Cori cycle shuttles lactate to the liver, where it is recycled into glucose (gluconeogenesis), creating a closed-loop energy system;
• Elite endurance athletes tend to have higher lactate thresholds, meaning they can produce and clear lactate efficiently: an adaptation, not a weakness.

Lactate and performance​

So, let’s see what the science has to say about lactate and performance:

Lactate supports high-intensity output​

During anaerobic activity, glycolysis produces lactate rapidly. Instead of being a dead-end, this lactate helps sustain energy demands when oxygen is limited;

Buffering capacity improves with training​

With regular exposure to lactate-producing workouts (e.g. intervals, tempo runs), the body becomes more efficient at buffering hydrogen ions and using lactate;

Lactate as a signaling molecule​

Lactate may play a role in cellular adaptation, including increased mitochondrial biogenesis and angiogenesis. Which just means better endurance and recovery;

Brain fuel during intense effort​

Under high stress or low oxygen, the brain can switch from glucose to lactate as a primary energy source, keeping mental performance sharp when it matters most.

However, to make lactate your ally and not your enemy, you need to train your body to handle and utilize it:

• Threshold training (aerobic zones 3-4): increases lactate clearance ability;
• High-intensity intervals: enhances lactate production and reuse efficiency;
• Tempo workouts: teach the body to perform with elevated lactate without crashing.

Lactate tolerance isn’t just for endurance athletes: sprinters, crossfitters, and bodybuilders can benefit by extending high-output windows and improving recovery between sets or bursts for example.

While lactate is most associated with endurance sports, its role in strength and hypertrophy is being explored:

• Metabolic stress (lactate buildup) is a known hypertrophy stimulus;
• Short rest periods and higher reps increase lactate, triggering growth factors like IGF-1;
• Occlusion training also leverages lactate accumulation for muscle growth with lighter loads, significantly reducing the chance of injury.

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In conclusion, lactic acid deserves a second look: not as a performance-limiting waste product, but as a key player in the body’s energy system. We’ve seen that lactate supports high-intensity output, fuels the brain and muscles, acts as a signaling molecule for adaptation, and even plays a role in hypertrophy for strength athletes. With proper training methods like threshold work and high-rep resistance training, you can train your body to not just tolerate lactate, but to improve on it. Under the right circumstances, lactic acid isn’t a barrier, but can be a bridge to higher levels of performance.

 

[BigTex]

Being that exercise science is my profession, I do have to dispute the statement that DOMS s caused by microscopic muscle damage, is simply not really true. The underlying mechanism of DOMS is still genuinely not fully resolved scientifically. Microscopic muscle damage is just one of many theories.

Muscle damage alone doesn't cleanly explain DOMS, because: Damage and soreness don't always correlate. Highly trained muscles can sustain significant damage with little soreness, and vice versa. Some studies show soreness without detectable structural damage, and damage without proportional soreness. The relationship between damage markers (like creatine kinase in blood) and perceived soreness is surprisingly weak.

The current thinking is that DOMS is likely multifactorial, involving some combination of (none of these have3 ever been proven and are still theory):
1. Mechanical damage triggering an inflammatory cascade, with sensitization of nociceptors (pain receptors) by bradykinin, prostaglandins, and other inflammatory mediators
2. Connective tissue damage — some researchers argue the pain comes more from damage to fascia and connective tissue around the muscle than the muscle fibers themselves
3. Calcium ion disruption — damaged cell membranes may allow calcium influx, activating proteases that extend cellular damage
4. Central sensitization — some evidence suggests the nervous system's pain processing is involved, not just peripheral tissue signals

So science has moved from "it's definitely lactate" to "it's definitely microscopic damage" to the current, more humble view: damage initiates a cascade, but exactly which signals produce the pain sensation, and why the response varies so much between individuals and training states, is still not fully understood. So yes — it remains genuinely theoretical at the mechanistic level.

Here is another statement I question - "Short rest periods and higher reps increase lactate, triggering growth facters like IGF-1." Current science agrees that high-rep, short-rest training does produce more metabolic stress and higher lactate accumulation. And there is an acute hormonal response to this kind of training. However, the leap from "acute hormonal spike" to "therefore more muscle growth" has been significantly challenged. A highly influential series of studies by Stuart Phillips and colleagues showed that the acute hormonal environment after training correlates poorly with actual muscle protein synthesis and long-term hypertrophy.

Systemic IGF-1 (measured in blood) may matter less than locally produced mechano-growth factor (MGF) within the muscle itself, which is more directly stimulated by mechanical tension than metabolic stress. Exercise science has shifted toward mechanical tension as the primary driver, with metabolic stress as a secondary or modulatory factor at best. Brad Schoenfeld's original framework proposed three mechanisms — mechanical tension, metabolic stress, and muscle damage — but subsequent research has elevated tension considerably above the other two. Which is why some of us old guys (like me) get no results from this light weight, high rep stuff.

Good stuff! Thanks for posting.